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Mingchu Xu, Lizhu Yang, Feng Wang, Huajin Li,3 Xia Wang, Weichen Wang, Zhongqi Ge, Keqing Wang, Li Zhao, Hui Li, Yumei Li, Ruifang Sui, and Rui Chen | Human Genetics | 28 July 2015 | Vol 134 | 1069–1078  |  ncbi.nlm.nih.gov/pmc/articles/PMC4565766/ In this study, we totally investigated seven unrelated non-syndromic RD patients, including five RP and two LCA cases. Among them, five of them are Han Chinese and the remaining two are of European ethnicity diagnosed in United States. The index case we investigated, SRF71, is a 43-year-old male RP patient of Han Chinese ethnicity. . .  Preliminary screening by retinal capture sequencing found no causative mutations in known RP-causing genes. WES data show that he has biallelic variants in IFT140,  . . . Abstract Leber congenital amaurosis (LCA) and retinitis pigmentosa (RP) are two genetically heterogeneous retinal degenerative disorders. Despite the identification of a number of genes involved in LCA and RP, the genetic etiology remains unknown in many patients. In this study, we aimed to identify novel disease-causing genes of LCA and RP. Retinal capture sequencing was initially performed to screen mutations in known disease-causing genes in different cohorts of LCA and RP patients. For patients with negative results, we performed whole exome sequencing and applied a series of variant filtering strategies. Sanger sequencing was done to validate candidate causative IFT140 variants. Exome sequencing data analysis led to the identification of IFT140 variants in multiple unrelated non-syndromic LCA and RP cases. All the variants are extremely rare and predicted to be damaging. All the variants passed Sanger validation and segregation tests provided that the family members’ DNA was available. The results expand the phenotype spectrum of IFT140 mutations to non-syndromic retinal degeneration, thus extending our understanding of intraflagellar transport and primary cilia biology in the retina. This work also improves the molecular diagnosis of retinal degenerative disease. Introduction Leber congenital amaurosis (LCA, MIM# 204000) and retinitis pigmentosa (RP, MIM# 268000) are two types of inherited retinal degenerative diseases. LCA is featured by congenital or infantile-onset vision loss, nystagmus and absent electroretinogram (ERG) signals. RP is a more common and variable form of retinal degeneration (RD) and its onset ranges from childhood to mid-adulthood ( Hartong et al. 2006 ). Both LCA and RP are highly genetically heterogeneous. To date, at least 21 LCA-causing and 64 RP-causing genes have been identified (RetNet, the Retinal Information Network) (SP Daiger). Mutations in these genes account for about 70 % of LCA and 60 % of RP cases, respectively, suggesting that the molecular basis of a significant number of cases is yet to be discovered ( Wang et al. 2013 , 2014 ). Retinal degenerative disorders can be syndromic, in which case patients develop symptoms in other systems in addition to their ocular abnormalities. This phenomenon is frequently seen in ciliopathies with retinal involvement since photoreceptors develop highly specialized cilia structure and ciliated cells are widespread in the human body ( Hildebrandt et al. 2011 ). Mutations in ciliary genes were identified in a number of syndromes with RD including Senior–Løken syndrome (SLSN, MIM# 266900) ( Otto et al. 2005 ), Joubert syndrome (JBTS, MIM# 213300) ( Dixon-Salazar et al. 2004 ), Bardet–Biedl syndrome (BBS, MIM#209900) ( Mykytyn et al. 2001 ). It has also been reported that mutations in syndromic ciliopathy genes can lead to non-syndromic LCA or RP. For example, IQCB1 mutations were originally identified to cause SLSN ( Otto et al. 2005 ), but certain IQCB1 mutant alleles were found to cause LCA without renal symptoms ( Estrada-Cuzcano et al. 2011 ). Similarly, while mutations in CEP290 , a cilia basal body gene, can cause a series of syndromic ciliopathies including JBTS and BBS ( Baala et al. 2007 ; Sayer et al. 2006 ; Valente et al. 2006 ), it is also a major contributor to non-syndromic LCA cases ( den Hollander et al. 2006 ). Given the fact that cilia are responsible for numerous biological processes in multiple tissues, the diverse genotype–phenotype correlations observed by these studies can be explained by a combination of multi-functional nature of these ciliary genes and differential damaging effect of their mutant alleles. Intraflagellar transport (IFT) is a biological process by which various proteins are transported along the microtubule-based cilia ( Rosenbaum and Witman 2002 ). Specifically, the IFT-A complex is responsible for the return of proteins from the ciliary tip ( Absalon et al. 2008 ). Defects in IFT-A particles have already been associated with a spectrum of human ciliopathies. Mutations in one IFT-A complex component, WDR19 , were reported to cause cranioectodermal dysplasia (CED, MIM# 614378) ( Bredrup et al. 2011 ), nephronophthisis (NPHP, MIM# 614377) ( Halbritter et al. 2013b ) as well as non-syndromic retinitis pigmentosa ( Coussa et al. 2013 ). Similarly, mutations in IFT140 , another IFT-A complex gene, were known to cause two types of rare recessive ciliopathies: Mainzer–Saldino syndrome (MZSDS, MIM# 266920) and Jeune asphyxiating thoracic dystrophy (JATD, MIM# 208500) ( Khan et al. 2014 ; Perrault et al. 2012 ; Schmidts et al. 2013 ). MZSDS is featured by cone-shaped epiphysis, chronic renal disease, abnormality of the proximal femur and RD ( Beals and Weleber 2007 ; Giedion 1979 ). JATD patients show constricted thoracic cage, short-limbed short stature, polydactyly and often develop multi-organ disorders including retinal abnormalities ( Bard et al. 1978 ; de Vries et al. 2010 ; Oberklaid et al. 1977 ). Since both WDR19 and IFT140 are linked to ciliopathies with retinal involvement, it is intriguing for us to know, whether IFT140 defects, like WDR19 mutations, can also cause non-syndromic RD. In this study, through whole exome sequencing (WES), mutations in IFT140 have been identified in seven patients diagnosed with non-syndromic LCA or RP. These patients come from diverse ethnicities and account for about 1 % of non-syndromic RD cases. Our results highlight a novel genotype–phenotype correlation of a ciliary gene, which can improve the molecular diagnosis of retinal degenerative diseases and our understanding of intraflagellar transport in the retina. Click here to read entire article References Absalon S, Blisnick T, Kohl L, Toutirais G, Dore G, Julkowska D, Tavenet A, Bastin P. Intraflagellar transport and functional analysis of genes required for flagellum formation in trypanosomes. Mol Biol Cell. 2008;19:929–944. doi: 10.1091/mbc.E07-08-0749. doi:10.1091/mbc.E07-08-0749. Adzhubei IA, Schmidt S, Peshkin L, Ramensky VE, Gerasimova A, Bork P, Kondrashov AS, Sunyaev SR. A method and server for predicting damaging missense mutations. Nat Methods. 2010;7:248–249. doi: 10.1038/nmeth0410-248. doi:10.1038/nmeth0410-248. Arts HH, Bongers EM, Mans DA, van Beersum SE, Oud MM, Bolat E, Spruijt L, Cornelissen EA, Schuurs-Hoeijmakers JH, de Leeuw N, Cormier-Daire V, Brunner HG, Knoers NV, Roepman R. C14ORF179 encoding IFT43 is mutated in Sensen-brenner syndrome. J Med Genet. 2011;48:390–395. doi: 10.1136/jmg.2011.088864. doi:10.1136/jmg.2011.088864. Baala L, Romano S, Khaddour R, Saunier S, Smith UM, Audol-lent S, Ozilou C, Faivre L, Laurent N, Foliguet B, Munnich A, Lyonnet S, Salomon R, Encha-Razavi F, Gubler MC, Boddaert N, de Lonlay P, Johnson CA, Vekemans M, Antignac C, Attie-Bitach T. The Meckel-Gruber syndrome gene, MKS3, is mutated in Joubert syndrome. Am J Hum Genet. 2007;80:186–194. doi: 10.1086/510499. doi:10.1086/510499. Badano JL, Kim JC, Hoskins BE, Lewis RA, Ansley SJ, Cutler DJ, Castellan C, Beales PL, Leroux MR, Katsanis N. Heterozygous mutations in BBS1, BBS2 and BBS6 have a potential epistatic effect on Bardet–Biedl patients with two mutations at a second BBS locus. Hum Mol Genet. 2003;12:1651–1659. doi: 10.1093/hmg/ddg188. Badano JL, Mitsuma N, Beales PL, Katsanis N. The ciliopathies: an emerging class of human genetic disorders. Annu Rev Genomics Hum Genet. 2006;7:125–148. doi: 10.1146/annurev.genom.7.080505.115610. doi:10.1146/annurev.genom.7.080505.115610. Bard LA, Bard PA, Owens GW, Hall BD. Retinal involvement in thoracic-pelvic-phalangeal dystrophy. Arch Ophthalmol. 1978;96:278–281. doi: 10.1001/archopht.1978.03910050146008. doi:10.1001/archopht.1978.03910050146008. Beals RK, Weleber RG. Conorenal dysplasia: a syndrome of cone-shaped epiphysis, renal disease in childhood, retinitis pigmentosa and abnormality of the proximal femur. Am J Med Genet Part A. 2007;143A:2444–2447. doi: 10.1002/ajmg.a.31948. doi:10.1002/ajmg.a.31948. Blain D, Goetz KE, Ayyagari R, Tumminia SJ. eyeGENE(R): a vision community resource facilitating patient care and paving the path for research through molecular diagnostic testing. Clin Genet. 2013;84:190–197. doi: 10.1111/cge.12193. doi:10.1111/cge.12193. Bredrup C, Saunier S, Oud MM, Fiskerstrand T, Hoischen A, Brackman D, Leh SM, Midtbo M, Filhol E, Bole-Feysot C, Nitschke P, Gilissen C, Haugen OH, Sanders JS, Stolte-Dijkstra I, Mans DA, Steenbergen EJ, Hamel BC, Matignon M, Pfundt R, Jeanpierre C, Boman H, Rodahl E, Veltman JA, Knappskog PM, Knoers NV, Roepman R, Arts HH. Ciliopathies with skeletal anomalies and renal insufficiency due to mutations in the IFT-A gene WDR19. Am J Hum Genet. 2011;89:634–643. doi: 10.1016/j.ajhg.2011.10.001. doi:10.1016/j.ajhg.2011.10.001. Bujakowska KM, Zhang Q, Siemiatkowska AM, Liu Q, Place E, Falk MJ, Consugar M, Lancelot ME, Antonio A, Lonjou C, Carpen-tier W, Mohand-Said S, den Hollander AI, Cremers FP, Leroy BP, Gai X, Sahel JA, van den Born LI, Collin RW, Zeitz C, Audo I, Pierce EA. Mutations in IFT172 cause isolated retinal degeneration and Bardet–Biedl syndrome. Hum Mol Genet. 2014 doi: 10.1093/hmg/ddu441. doi:10.1093/hmg/ddu441. Chun S, Fay JC. Identification of deleterious mutations within three human genomes. Genome Res. 2009;19:1553–1561. doi: 10.1101/gr.092619.109. doi:10.1101/gr.092619.109. Coene KL, Roepman R, Doherty D, Afroze B, Kroes HY, Letteboer SJ, Ngu LH, Budny B, van Wijk E, Gorden NT, Azhimi M, Thauvin-Robinet C, Veltman JA, Boink M, Kleefstra T, Cremers FP, van Bokhoven H, de Brouwer AP. OFD1 is mutated in X-linked Joubert syndrome and interacts with LCA5-encoded lebercilin. Am J Hum Genet. 2009;85:465–481. doi: 10.1016/j.ajhg.2009.09.002. doi:10.1016/j.ajhg.2009.09.002. Coussa RG, Otto EA, Gee HY, Arthurs P, Ren H, Lopez I, Keser V, Fu Q, Faingold R, Khan A, Schwartzentruber J, Majewski J, Hilde-brandt F, Koenekoop RK. WDR19: an ancient, retrograde, intraflagellar ciliary protein is mutated in autosomal recessive retinitis pigmentosa and in Senior–Loken syndrome. Clin Genet. 2013;84:150–159. doi: 10.1111/cge.12196. doi:10.1111/cge.12196. Crouse JA, Lopes VS, Sanagustin JT, Keady BT, Williams DS, Pazour GJ. Distinct functions for IFT140 and IFT20 in opsin transport. Cytoskeleton (Hoboken) 2014;71:302–310. doi: 10.1002/cm.21173. doi:10.1002/cm.21173. Daiger SPBR, Greenberg J, Christoffels A, Hide W. [30th Jan 2015]; RetNet. http://www.sph.uth.tmc.edu/RetNet/ . D'Andrea LD, Regan L. TPR proteins: the versatile helix. Trends Biochem Sci. 2003;28:655–662. doi: 10.1016/j.tibs.2003.10.007. doi:10.1016/j.tibs.2003.10.007. [ DOI ] [ PubMed ] [ Google Scholar ] Davis EE, Zhang Q, Liu Q, Diplas BH, Davey LM, Hartley J, Stoetzel C, Szymanska K, Ramaswami G, Logan CV, Muzny DM, Young AC, Wheeler DA, Cruz P, Morgan M, Lewis LR, Cherukuri P, Maskeri B, Hansen NF, Mullikin JC, Blakesley RW, Bouffard GG, Program NCS, Gyapay G, Rieger S, Tonshoff B, Kern I, Soliman NA, Neuhaus TJ, Swoboda KJ, Kayserili H, Gallagher TE, Lewis RA, Bergmann C, Otto EA, Saunier S, Scambler PJ, Beales PL, Gleeson JG, Maher ER, Attie-Bitach T, Dollfus H, Johnson CA, Green ED, Gibbs RA, Hildebrandt F, Pierce EA, Katsanis N. TTC21B contributes both causal and modifying alleles across the ciliopathy spectrum. Nat Genet. 2011;43:189–196. doi: 10.1038/ng.756. doi:10.1038/ng.756. de Vries J, Yntema JL, van Die CE, Crama N, Cornelissen EA, Hamel BC. Jeune syndrome: description of 13 cases and a proposal for follow-up protocol. Eur J Pediatr. 2010;169:77–88. doi: 10.1007/s00431-009-0991-3. doi:10.1007/s00431-009-0991-3. den Hollander AI, Koenekoop RK, Yzer S, Lopez I, Arends ML, Voesenek KE, Zonneveld MN, Strom TM, Meitinger T, Brunner HG, Hoyng CB, van den Born LI, Rohrschneider K, Cremers FP. Mutations in the CEP290 (NPHP6) gene are a frequent cause of Leber congenital amaurosis. Am J Hum Genet. 2006;79:556–561. doi: 10.1086/507318. doi:10.1086/507318. Dixon-Salazar T, Silhavy JL, Marsh SE, Louie CM, Scott LC, Gururaj A, Al-Gazali L, Al-Tawari AA, Kayserili H, Sztriha L, Gleeson JG. Mutations in the AHI1 gene, encoding jouberin, cause Joubert syndrome with cortical polymicrogyria. Am J Hum Genet. 2004;75:979–987. doi: 10.1086/425985. doi:10.1086/425985. Estrada-Cuzcano A, Koenekoop RK, Coppieters F, Kohl S, Lopez I, Collin RW, De Baere EB, Roeleveld D, Marek J, Bernd A, Rohr-schneider K, van den Born LI, Meire F, Maumenee IH, Jacobson SG, Hoyng CB, Zrenner E, Cremers FP, den Hollander AI. IQCB1 mutations in patients with leber congenital amaurosis. Invest Ophthalmol Vis Sci. 2011;52:834–839. doi: 10.1167/iovs.10-5221. doi:10.1167/iovs.10-5221. Follit JA, Xu F, Keady BT, Pazour GJ. Characterization of mouse IFT complex B. Cell Motil Cytoskeleton. 2009;66:457–468. doi: 10.1002/cm.20346. doi:10.1002/cm.20346. Giedion A. Phalangeal cone shaped epiphysis of the hands (PhCSEH) and chronic renal disease—the conorenal syndromes. Pediatr Radiol. 1979;8:32–38. doi: 10.1007/BF00973675. doi:10.1007/BF00973675. Halbritter J, Bizet AA, Schmidts M, Porath JD, Braun DA, Gee HY, McInerney-Leo AM, Krug P, Filhol E, Davis EE, Airik R, Czar-necki PG, Lehman AM, Trnka P, Nitschke P, Bole-Feysot C, Schueler M, Knebelmann B, Burtey S, Szabo AJ, Tory K, Leo PJ, Gardiner B, McKenzie FA, Zankl A, Brown MA, Hartley JL, Maher ER, Li C, Leroux, Scambler PJ, Zhan SH, Jones SJ, Kayserili H, Tuysuz B, Moorani KN, Constantinescu A, Krantz ID, Kaplan BS, Shah JV, Consortium UK, Hurd TW, Doherty D, Katsanis N, Duncan EL, Otto EA, Beales PL, Mitchison HM, Saunier S, Hildebrandt F. Defects in the IFT-B component IFT172 cause Jeune and Mainzer–Saldino syndromes in humans. Am J Hum Genet. 2013a;93:915–925. doi: 10.1016/j.ajhg.2013.09.012. doi:10.1016/j.ajhg.2013.09.012. Halbritter J, Porath JD, Diaz KA, Braun DA, Kohl S, Chaki M, Allen SJ, Soliman NA, Hildebrandt F, Otto EA. Identification of 99 novel mutations in a worldwide cohort of 1,056 patients with a nephronophthisis-related ciliopathy. Hum Genet. 2013b;132:865–884. doi: 10.1007/s00439-013-1297-0. doi:10.1007/s00439-013-1297-0. Hartong DT, Berson EL, Dryja TP. Retinitis pigmentosa. Lancet. 2006;368:1795–1809. doi: 10.1016/S0140-6736(06)69740-7. doi:10.1016/s0140-6736(06)69740-7. Hildebrandt F, Benzing T, Katsanis N. Ciliopathies. N Engl J Med. 2011;364:1533–1543. doi: 10.1056/NEJMra1010172. doi:10.1056/NEJMra1010172. Katsanis N. The oligogenic properties of Bardet–Biedl syndrome. Hum Mol Genet 13 Spec No. 2004;1:R65–R71. doi: 10.1093/hmg/ddh092. doi:10.1093/hmg/ddh092. Keady BT, Le YZ, Pazour GJ. IFT20 is required for opsin trafficking and photoreceptor outer segment development. Mol Biol Cell. 2011;22:921–930. doi: 10.1091/mbc.E10-09-0792. doi:10.1091/mbc.E10-09-0792. Khan AO, Bolz HJ, Bergmann C. Early-onset severe retinal dystrophy as the initial presentation of IFT140-related skeletal ciliopathy. J aapos. 2014;18:203–205. doi: 10.1016/j.jaapos.2013.11.016. doi:10.1016/j.jaapos.2013.11.016. Krock BL, Perkins BD. The intraflagellar transport protein IFT57 is required for cilia maintenance and regulates IFT-particle-kinesin-II dissociation in vertebrate photoreceptors. J Cell Sci. 2008;121:1907–1915. doi: 10.1242/jcs.029397. doi:10.1242/jcs.029397. Li H, Durbin R. Fast and accurate short read alignment with Burrows-Wheeler transform. Bioinformatics. 2009;25:1754–1760. doi: 10.1093/bioinformatics/btp324. doi:10.1093/bioinformatics/btp324. Marszalek JR, Liu X, Roberts EA, Chui D, Marth JD, Williams DS, Goldstein LS. Genetic evidence for selective transport of opsin and arrestin by kinesin-II in mammalian photoreceptors. Cell. 2000;102:175–187. doi: 10.1016/s0092-8674(00)00023-4. Mill P, Lockhart PJ, Fitzpatrick E, Mountford HS, Hall EA, Reijns MA, Keighren M, Bahlo M, Bromhead CJ, Budd P, Aftimos S, Delatycki MB, Savarirayan R, Jackson IJ, Amor DJ. Human and mouse mutations in WDR35 cause short-rib polydactyly syndromes due to abnormal ciliogenesis. Am J Hum Genet. 2011;88:508–515. doi: 10.1016/j.ajhg.2011.03.015. doi:10.1016/j.ajhg.2011.03.015. Miller KA, Ah-Cann CJ, Welfare MF, Tan TY, Pope K, Caruana G, Freckmann ML, Savarirayan R, Bertram JF, Dobbie MS, Bateman JF, Farlie PG. Cauli: a mouse strain with an Ift140 mutation that results in a skeletal ciliopathy modelling Jeune syndrome. PLoS Genet. 2013;9:e1003746. doi: 10.1371/journal.pgen.1003746. doi:10.1371/journal.pgen.1003746. Mykytyn K, Braun T, Carmi R, Haider NB, Searby CC, Shastri M, Beck G, Wright AF, Iannaccone A, Elbedour K, Riise R, Baldi A, Raas-Rothschild A, Gorman SW, Duhl DM, Jacobson SG, Casavant T, Stone EM, Sheffield VC. Identification of the gene that, when mutated, causes the human obesity syndrome BBS4. Nat Genet. 2001;28:188–191. doi: 10.1038/88925. doi:10.1038/88925. Ng PC, Henikoff S. SIFT: predicting amino acid changes that affect protein function. Nucleic Acids Res. 2003;31:3812–3814. doi: 10.1093/nar/gkg509. Oberklaid F, Danks DM, Mayne V, Campbell P. Asphyxiating thoracic dysplasia. Clinical, radiological, and pathological information on 10 patients. Arch Dis Child. 1977;52:758–765. doi: 10.1136/adc.52.10.758. doi:10.1136/adc.52.10.758. Otto EA, Loeys B, Khanna H, Hellemans J, Sudbrak R, Fan S, Muerb U, O'Toole JF, Helou J, Attanasio M, Utsch B, Sayer JA, Lillo C, Jimeno D, Coucke P, De Paepe A, Reinhardt R, Klages S, Tsuda M, Kawakami I, Kusakabe T, Omran H, Imm A, Tippens M, Raymond PA, Hill J, Beales P, He S, Kispert A, Margolis B, Williams DS, Swaroop A, Hildebrandt F. Nephrocystin-5, a ciliary IQ domain protein, is mutated in Senior–Loken syndrome and interacts with RPGR and calmodulin. Nat Genet. 2005;37:282–288. doi: 10.1038/ng1520. doi:10.1038/ng1520. Perrault I, Saunier S, Hanein S, Filhol E, Bizet AA, Collins F, Salih MA, Gerber S, Delphin N, Bigot K, Orssaud C, Silva E, Baudouin V, Oud MM, Shannon N, Le Merrer M, Roche O, Pietrement C, Goumid J, Baumann C, Bole-Feysot C, Nitschke P, Zahrate M, Beales P, Arts HH, Munnich A, Kaplan J, Antignac C, Cormier-Daire V, Rozet JM. Mainzer–Saldino syndrome is a ciliopathy caused by IFT140 mutations. Am J Hum Genet. 2012;90:864–870. doi: 10.1016/j.ajhg.2012.03.006. doi:10.1016/j.ajhg.2012.03.006. Reva B, Antipin Y, Sander C. Predicting the functional impact of protein mutations: application to cancer genomics. Nucl Acids Res. 2011;39:e118. doi: 10.1093/nar/gkr407. doi:10.1093/nar/gkr407. Riazuddin SA, Iqbal M, Wang Y, Masuda T, Chen Y, Bowne S, Sullivan LS, Waseem NH, Bhattacharya S, Daiger SP, Zhang K, Khan SN, Riazuddin S, Hejtmancik JF, Sieving PA, Zack DJ, Katsanis N. A splice-site mutation in a retina-specific exon of BBS8 causes nonsyndromic retinitis pigmentosa. Am J Hum Genet. 2010;86:805–812. doi: 10.1016/j.ajhg.2010.04.001. doi:10.1016/j.ajhg.2010.04.001. Rosenbaum JL, Witman GB. Intraflagellar transport. Nat Rev Mol Cell Biol. 2002;3:813–825. doi: 10.1038/nrm952. doi:10.1038/nrm952. Sayer JA, Otto EA, O'Toole JF, Nurnberg G, Kennedy MA, Becker C, Hennies HC, Helou J, Attanasio M, Fausett BV, Utsch B, Khanna H, Liu Y, Drummond I, Kawakami I, Kusakabe T, Tsuda M, Ma L, Lee H, Larson RG, Allen SJ, Wilkinson CJ, Nigg EA, Shou C, Lillo C, Williams DS, Hoppe B, Kemper MJ, Neuhaus T, Parisi MA, Glass IA, Petry M, Kispert A, Gloy J, Ganner A, Walz G, Zhu X, Goldman D, Nurnberg P, Swaroop A, Leroux MR, Hildebrandt F. The centrosomal protein nephrocystin-6 is mutated in Joubert syndrome and activates transcription factor ATF4. Nat Genet. 2006;38:674–681. doi: 10.1038/ng1786. doi:10.1038/ng1786. Schmidts M, Frank V, Eisenberger T, Al Turki S, Bizet AA, Antony D, Rix S, Decker C, Bachmann N, Bald M, Vinke T, Toenshoff B, Di Donato N, Neuhann T, Hartley JL, Maher ER, Bogdanovic R, Peco-Antic A, Mache C, Hurles ME, Joksic I, Guc-Scekic M, Dobricic J, Brankovic-Magic M, Bolz HJ, Pazour GJ, Beales PL, Scambler PJ, Saunier S, Mitchison HM, Bergmann C. Combined NGS approaches identify mutations in the intraflagellar transport gene IFT140 in skeletal ciliopathies with early progressive kidney Disease. Hum Mutat. 2013;34:714–724. doi: 10.1002/humu.22294. doi:10.1002/humu.22294. Schwarz JM, Rodelsperger C, Schuelke M, Seelow D. MutationTaster evaluates disease-causing potential of sequence alterations. Nat Methods. 2010;7:575–576. doi: 10.1038/nmeth0810-575. doi:10.1038/nmeth0810-575. Smit A, Hubley R, Green P. [30 Dec 2014];RepeatMasker Open-3.0. 1996–2010 Untergasser A, Cutcutache I, Koressaar T, Ye J, Faircloth BC, Remm M, Rozen SG. Primer3—new capabilities and interfaces. Nucl Acids Res. 2012;40:e115. doi: 10.1093/nar/gks596. doi:10.1093/nar/gks596. Valente EM, Silhavy JL, Brancati F, Barrano G, Krishnaswami SR, Castori M, Lancaster MA, Boltshauser E, Boccone L, Al-Gazali L, Fazzi E, Signorini S, Louie CM, Bellacchio E, Bertini E, Dallapiccola B, Gleeson JG. Mutations in CEP290, which encodes a centrosomal protein, cause pleiotropic forms of Jou-bert syndrome. Nat Genet. 2006;38:623–625. doi: 10.1038/ng1805. doi:10.1038/ng1805. Walczak-Sztulpa J, Eggenschwiler J, Osborn D, Brown DA, Emma F, Klingenberg C, Hennekam RC, Torre G, Garshasbi M, Tzschach A, Szczepanska M, Krawczynski M, Zachwieja J, Zwolinska D, Beales PL, Ropers HH, Latos-Bielenska A, Kuss AW. Cranioectodermal Dysplasia, Sensenbrenner syndrome, is a ciliopathy caused by mutations in the IFT122 gene. Am J Hum Genet. 2010;86:949–956. doi: 10.1016/j.ajhg.2010.04.012. doi:10.1016/j.ajhg.2010.04.012. Wang X, Wang H, Sun V, Tuan HF, Keser V, Wang K, Ren H, Lopez I, Zaneveld JE, Siddiqui S, Bowles S, Khan A, Salvo J, Jacobson SG, Iannaccone A, Wang F, Birch D, Heckenlively JR, Fishman GA, Traboulsi EI, Li Y, Wheaton D, Koenekoop RK, Chen R. Comprehensive molecular diagnosis of 179 Leber congenital amaurosis and juvenile retinitis pigmentosa patients by targeted next generation sequencing. J Med Genet. 2013;50:674–688. doi: 10.1136/jmedgenet-2013-101558. doi:10.1136/jmedgenet-2013-101558. Wang F, Wang H, Tuan HF, Nguyen DH, Sun V, Keser V, Bowne SJ, Sullivan LS, Luo H, Zhao L, Wang X, Zaneveld JE, Salvo JS, Siddiqui S, Mao L, Wheaton DK, Birch DG, Branham KE, Heckenlively JR, Wen C, Flagg K, Ferreyra H, Pei J, Khan A, Ren H, Wang K, Lopez I, Qamar R, Zenteno JC, Ayala-Ramirez R, Buentello-Volante B, Fu Q, Simpson DA, Li Y, Sui R, Silvestri G, Daiger SP, Koenekoop RK, Zhang K, Chen R. Next generation sequencing-based molecular diagnosis of retinitis pigmentosa: identification of a novel genotype-phenotype correlation and clinical refinements. Hum Genet. 2014;133:331–345. doi: 10.1007/s00439-013-1381-5. doi:10.1007/s00439-013-1381-5. Xu C, Min J. Structure and function of WD40 domain proteins. Protein Cell. 2011;2:202–214. doi: 10.1007/s13238-011-1018-1. doi:10.1007/s13238-011-1018-1. Xu M, Gelowani V, Eblimit A, Wang F, Young MP, Sawyer BL, Zhao L, Jenkins G, Creel DJ, Wang K, Ge Z, Wang H, Li Y, Hartnett ME, Chen R. ATF6 is mutated in early onset photoreceptor degeneration with macular involvement. Invest Ophthalmol Vis Sci. 2015;56:3889–3895. doi: 10.1167/iovs.15-16778. doi:10.1167/iovs.15-16778. Young RW. Visual cells and the concept of renewal. Invest Ophthalmol Vis Sci. 1976;15:700–725.

S. Goyal ,  M. Jäger ,  P.N. Robinson ,  V. Vanita | Clinical Genetics | 21 July 2015 | Vol. 89, Issue 4 | pgs. 454-460 | https://doi.org/10.1111/cge.12644 Abstract Nonsyndromic retinitis pigmentosa (RP) is genetically highly heterogeneous, with >100 disease genes identified. However, mutations in these genes explain only 60% of all RP cases. Blood samples were collected from 12 members of an autosomal recessive RP family. Whole genome homozygosity mapping and haplotype analysis placed the RP locus in this family at chromosome 14q31.3. Whole-exome sequencing (WES) in proband revealed a mutation in TTC8 , which was flagged as most likely candidate gene by bioinformatic analysis. TTC8 is mutated in Bardet–Biedl syndrome 8 (BBS8), and once reported previously in a family with nonsyndromic RP. Sequencing of amplified products of exon 13 of TTC8 validated c.1347G>C (p.Gln449His), a novel change that affects the final nucleotide of exon 13 and might deleteriously affect splicing. This mutation segregated completely with the disease in the family and was not observed in 100 ethnically matched controls from same population. This represents second report of a TTC8 mutation in nonsyndromic RP, thus confirming the identity of TTC8 as causative gene for RP51. Click here to buy article

Relatively Common Cause of Autosomal Recessive Early-Onset Retinal Degeneration in the Israeli and Palestinian Populations Avigail Beryozkin, Lina Zelinger, Dikla Bandah-Rozenfeld, Anat Harel, Tim A. Strom, Saul Merin, Itay Chowers, Eyal Banin, Dror Sharon | Investigative Ophthalmology & Visual Science | March 2013 | Vol.54 | 2068-2075 | Introduction Mutations in Crumbs homolog 1 (CRB1) are known to cause severe retinal dystrophies, ranging from Leber congenital amaurosis (LCA) to retinitis pigmentosa (RP). (1–7) LCA is the most severe nonsyndromic retinal dystrophy, characterized by blindness or severe visual impairment from birth, nonrecordable electroretinogram (ERG), nystagmus, hypermetropia, sluggish or absent pupillary responses, and oculodigital reflexes. (2,4–6,8) In contrast, RP is considered a milder and more heterogeneous disorder, with a later age of onset. It is characterized by night blindness followed by gradual loss of peripheral vision, progressive degeneration of photoreceptors, and eventually leads to visual impairment of variable severity that in rare cases can result in complete blindness. (9–12) Patients with RP have impaired ERG responses with a rod > cone pattern of injury, and over time suffer characteristic funduscopic findings, including bone spicule–like pigmentary (BSP) changes, attenuation of retinal vessels, and waxy pallor of the optic discs. (9–12) Retinal dystrophies resulting from CRB1 mutations can be accompanied by additional specific features, including relative preservation of the para-arteriolar retinal pigment epithelium (PPRPE) and Coats-like vasculopathy. (1–5,8,13,14) RP with PPRPE is a form of RP characterized by preservation of the RPE that is adjacent to the retinal arterioles, while the rest of the RPE layer degenerates. Coats-like exudative vasculopathy is characterized by abnormal retinal vessels with increased permeability, leading to exudative retinal detachment that often is accompanied by massive subretinal lipid deposits. 3–5,7,13,15 CRB1 is a human homologue of the drosophila transmembrane crumbs protein, and is expressed in the brain and in the inner segments of mammalian photoreceptors. (2,3,7,16–19) The Crumbs protein is implicated in mechanisms that control cell-cell adhesion, intracellular communication and apicobasal cell polarity. For epithelial cells and photoreceptors, separation of their apical and basal compartments is critical for proper development and function of the cells and the tissue, including adhesion and signaling between and within cells.(2,7,13,16–19) Jacobson et al. suggested that CRB1 mutations underlie developmental defects in LCA, including thickening of the retina and lack of distinct layering in the fully developed adult retina.(13) Rashbass et al. postulated that CRB1 has a role in localizing phototransduction proteins to the apical membrane of the photoreceptors. 18 Thus, nonfunctional CRB1 may impede phototransduction, and lead to progressive dystrophy of the photoreceptors and the RPE, resulting in LCA or RP. Read the article References 1. Bujakowska K Audo I Mohand-Said S CRB1 mutations in inherited retinal dystrophies. Hum Mutat . 2011; 33: 306–315. 2. Gosens I den Hollander AI Cremers FP Roepman R. Composition and function of the Crumbs protein complex in the mammalian retina. Exp Eye Res . 2008; 86: 713–726. 3. den Hollander AI ten Brink JB de Kok YJ Mutations in a human homologue of Drosophila crumbs cause retinitis pigmentosa (RP12). Nat Genet . 1999; 23: 217–221. 4. den Hollander AI Heckenlively JR van den Born LI Leber congenital amaurosis and retinitis pigmentosa with Coats-like exudative vasculopathy are associated with mutations in the crumbs homologue 1 (CRB1) gene. Am J Hum Genet . 2001; 69: 198–203. 5. den Hollander AI Davis J van der Velde-Visser SD CRB1 mutation spectrum in inherited retinal dystrophies. Hum Mutat . 2004; 24: 355–369. 6. den Hollander AI Roepman R Koenekoop RK Cremers FP. Leber congenital amaurosis: genes, proteins and disease mechanisms. Prog Retin Eye Res . 2008; 27: 391–419. 7. Richard M Roepman R Aartsen WM Towards understanding CRUMBS function in retinal dystrophies. Hum Mol Genet . 2006; 15 (spec No 2): R235–R243. 8. Simonelli F Ziviello C Testa F Clinical and molecular genetics of Leber's congenital amaurosis: a multicenter study of Italian patients. Invest Ophthalmol Vis Sci . 2007; 48: 4284–4290. 9. Berson EL. Retinitis pigmentosa. The Friedenwald Lecture. Invest Ophthalmol Vis Sci . 1993; 34: 1659–1676. 10. Bhatti MT. Retinitis pigmentosa, pigmentary retinopathies, and neurologic diseases. Curr Neurol Neurosci Rep . 2006; 6: 403–413. 11. Hartong DT Berson EL Dryja TP. Retinitis pigmentosa. Lancet . 2006; 368: 1795–1809. 12.Jacobson SG Roman AJ Aleman TS Normal central retinal function and structure preserved in retinitis pigmentosa. Invest Ophthalmol Vis Sci . 2010; 51: 1079–1085. 13. Jacobson SG Cideciyan AV Aleman TS Crumbs homolog 1 (CRB1) mutations result in a thick human retina with abnormal lamination. Hum Mol Genet . 2003; 12: 1073–1078. 14. Siemiatkowska AM Arimadyo K Moruz LM Molecular genetic analysis of retinitis pigmentosa in Indonesia using genome-wide homozygosity mapping. Mol Vis . 2011; 17: 3013–3024. 15. Cahill M O'Keefe M Acheson R Classification of the spectrum of Coats' disease as subtypes of idiopathic retinal telangiectasis with exudation. Acta Ophthalmol Scand . 2001; 79: 596–602. 16.Davis JA Handford PA Redfield C. The N1317H substitution associated with Leber congenital amaurosis results in impaired interdomain packing in human CRB1 epidermal growth factor-like (EGF) domains. J Biol Chem . 2007; 282: 28807–28814. 17. den Hollander AI Johnson K de Kok YJ CRB1 has a cytoplasmic domain that is functionally conserved between human and Drosophila. Hum Mol Genet . 2001; 10: 2767–2773. 18. Rashbass P Skaer H. Cell polarity: nailing Crumbs to the scaffold. Curr Biol . 2000; 10: R234–R236.

Abstract Retina and retinal pigment epithelium (RPE) belong to the metabolically most active tissues in the human body. Efficient removal of acid load from retina and RPE is a critical function mediated by the choriocapillaris. However, the mechanism by which pH homeostasis is maintained is largely unknown. Here, we show that a functional complex of carbonic anhydrase 4 (CA4) and Na+/bicarbonate co-transporter 1 (NBC1) is specifically expressed in the choriocapillaris and that missense mutations in CA4 linked to autosomal dominant rod–cone dystrophy disrupt NBC1-mediated HCO3−transport. Our results identify a novel pathogenic pathway in which a defect in a functional complex involved in maintaining pH balances, but not expressed in retina or RPE, leads to photoreceptor degeneration. The importance of a functional CA4 for survival of photoreceptors implies that CA inhibitors, which are widely used as medications, particularly in the treatment of glaucoma, may have long-term adverse effects on vision. Read more

Michael Danciger, Vickie Heilbron, Yong-Qing Gao, Dan-Yun Zhao, Samuel G. Jacobson, and Debora B. Farber | Mol. Vis. | Volume 2 (10) | 1996 |  molvis.org/molvis/v2/a10/ Based on average estimates of the prevalence of non-syndromic  retinitis pigmentosa  (RP) at 1/4,000, there are approximately 1.5 million people in the world with this inherited, progressive, degenerative disease of the retinal photoreceptor cells which often leads to blindness. About 50% of these cases are inherited in an autosomal recessive manner (AR). With the approach of screening the exons of candidate genes in large numbers of unrelated ARRP probands, mutations associated with disease have been found in several candidate genes expressed in rod photoreceptors at very low frequency:  RHO , encoding rhodopsin, 1/126 patients screened;  PDE6B (click to continue reading) Based on average estimates of the prevalence of non-syndromic retinitis pigmentosa (RP) at 1/4,000, there are approximately 1.5 million people in the world with this inherited, progressive, degenerative disease of the retinal photoreceptor cells which often leads to blindness (1,2,3). About 50% of these cases are inherited in an autosomal recessive manner (AR). With the approach of screening the exons of candidate genes in large numbers of unrelated ARRP probands, mutations associated with disease have been found in several candidate genes expressed in rod photoreceptors at very low frequency: RHO , encoding rhodopsin, 1/126 patients screened (4); PDE6B , encoding the beta-subunit of rod cGMP-phosphodiesterase, 4/88 patients (5); PDE6A , encoding the alpha-subunit of rod cGMP-phosphodiesterase, 2/173 patients (6); and CNCG , encoding the alpha-subunit of the rod cGMP-gated channel, 3/173 patients (7). With the approach of linkage analysis in large families, two ARRP loci have so far been discovered: 1q31-q32.1 (8,9) and 6p, distal to RDS-peripherin (10). Also, linkage analysis of an informative consanguineous family led to the discovery of a second homozygous RHO mutation (11). ARRP tends to appear most often in small nuclear families that by themselves are not informative enough to yield significant linkage data, and screening all the exons of candidate genes like PDE6A and PDE6B (each with 22 exons) in large numbers of unrelated probands is costly and time consuming. Therefore, we have taken the approach of studying candidate genes in small nuclear ARRP families with a double screening protocol. Linkage analyses of markers close to the loci of the candidate genes are performed first, and any families where a gene locus clearly does not segregate with disease are ruled out from further study of that gene. DNAs of the probands from the remaining families (where the gene locus cannot be ruled out from segregating with disease) are then screened for mutations in the exons of the candidate gene by SSCPE (single strand conformation polymorphism electrophoresis) and DGGE (denaturing gradient gel electrophoresis). Any exonic variants found are sequenced directly and analyzed within the corresponding family to see if they appear to segregate with disease. With this approach we studied 24 families with inherited retinal degenerations (14 with typical RP) for mutations in the genes PDE6B, MYL5 , PDE6C, CNCG , RHO, ROM1 and RDS-peripherin . We have reported two typical ARRP families where the affecteds uniquely inherited compound heterozygous mutations in the PDE6B gene (12). With a similar approach, homozygous mutations also have been found in PDE6B in the affecteds of two other ARRP families (13,14). Click here to read more References Kumar-Singh, R, Farrar GJ, Mansergh, F. Kenna, P. Bhattacharya, S, Gal, A, and Humphries, P, Exclusion of the involvement of all known retinitis pigmentosa loci in the disease present in a family of Irish origin provides evidence for a sixth autosomal dominant locus (RP8). Hum. Mol. Genet. 7 (1993) 875-878 . Bundey, S and Crews, SSJ, A study of retinitis pigmentosa in the City of Birmingham. I Prevalence. J. Med. Genet. 21 (1984) 417-420. Boughman, JA, Conneally, PM and Nance WE, Population genetic studies of retinitis pigmentosa. Am. J. Hum. Genet. 32 (1980) 223-235. Rosenfeld, PJ, Cowley, GS, McGee, TL, Sandberg, MA, Berson, EL and Dryja, TP, A null mutation in the rhodopsin gene causes rod photoreceptor dysfunction and autosomal recessive retinitis pigmentosa. Nature Genet. 1 (1992) 209-213. McLaughlin, ME, Sandberg, MA, Berson, EL and Dryja TP, Recessive mutations in the gene encoding the beta-subunit of rod phosphodiesterase in patients with retinitis pigmentosa. Nature Genet. 4 (1993) 130-134. Huang, SH, Pittler, SJ, Huang, X, Oliveira, L, Berson, EL and Dryja, TP, Autosomal recessive retinitis pigmentosa caused by mutations in the a subunit of rod cGMP phosphodiesterase. Nature Genet. 11 (1995) 468-471. Dryja, TP, Finn, JT, Peng, Y-W, McGee, TL, Berson, EL and Yau, K-W, Mutations in the gene encoding the a subunit of the rod cGMP-gated channel in autosomal recessive retinitis pigmentosa. Proc. Nat. Acad. Sci. USA 92 (1995) 10177-10181. van Soest, S, Ingeborgh van den Born, L, Gal, A, Farrar, GJ, Bleeker- Wagemakers, LM, Westerveld, A, Humphries, P, Sandkuijl, LA and Bergen, AB, Assignment of a gene for autosomal recessive retinitis pigmentosa (RP12) to chromosome 1q31-q32.1 in an inbred and genetically heterogeneous disease population. Genomics 22 (1994) 499-504. Leutelt, J, Oehlman, R, Younus, F, Ingeborgh van den Born, L, Weber, JL, Denton, MJ, Qasim Mehdi, S and Gal, A, Autosomal recessive retinitis pigmentosa locus maps on chromosome 1q in a large consanguineous family from Pakistan. Clin. Genet. 47 (1995) 122-124. Knowles, JA, Shugart, Y, Banerjee, P, Gilliam, TC, Lewis, CA, Jacobson, SG and Ott, J, Identification of a locus, distinct from RDS-peripherin, for autosomal recessive retinitis pigmentosa on chromosome 6p. Hum. Mol. Genet. 3 (1994) 1402-1403. Kumaramanickavel, G, Maw, M, Denton, MJ, John, S, Srikumari, CR, Orth, U, Oehlman, R and Gal, A, Missense rhodopsin mutation in a family with recessive RP. Nature Genet. 8 (1994) 10-11. Danciger, M, Blaney, J, Gao, Y-Q, Zhao, DY, Heckenlively, JR, Jacobson, SG and Farber, DB, Mutations in the PDE6B gene in autosomal recessive RP. Genomics 30 (1995) 1-7. Bayes, M, Giordano, M, Balcells, S, Grinberg, S, Vilageliu, L, Martinez, I, Ayuso, C, Benitez, J, Ramos-Arroyo, MA, Chivelet, P, Solans, T, Valverde, D, Amselem, S, Goosens, M, Baiget, M, Gonzalez-Duarte, R and Besmond, C, Homozygous tandem duplication within the gene encoding the beta-subunit of rod phosphodiesterase as a cause for autosomal recessive retinitis pigmentosa. Human Mutation 5 (1995) 228-234. Valverde, D, Solans, T, Grinberg, S, Balcells, S,Vilageliu, L, Bayes, M, Chivelet, P, Besmond, C, Goosens, Gonzalez-Duarte, R and Baiget, M, A novel mutation in exon 17 of the beta-subunit of rod phosphodiesterase in two RP sisters of a consanguineous family. Human Genet. 97 (1996) 35-38.

Camiel J F Boon   1 ,  B Jeroen Klevering ,  Bart P Leroy ,  Carel B Hoyng ,  Jan E E Keunen ,  Anneke I den Hollander | Prog Retin Eye Res | 2009 May |28(3) | Pages 187-205 | doi: 10.1016/j.preteyeres.2009.04.002 Abstract Bestrophin-1 is an integral membrane protein, encoded by the BEST1 gene, which is located in the basolateral membrane of the retinal pigment epithelium. The bestrophin-1 protein forms a Ca(2+) activated Cl(-) channel and is involved in the regulation of voltage-dependent Ca(2+) channels. In addition, bestrophin-1 appears to play a role in ocular development. Over 120 different human BEST1 mutations have been described to date, associated with a broad range of ocular phenotypes. The purpose of this review is to describe this spectrum of phenotypes, which includes Best vitelliform macular dystrophy and adult-onset foveomacular vitelliform dystrophy, autosomal dominant vitreoretinochoroidopathy, the MRCS (microcornea, rod-cone dystrophy, cataract, posterior staphyloma) syndrome, and autosomal recessive bestrophinopathy. The genotype-phenotype correlations that are observed in association with BEST1 mutations are discussed. In addition, in vitro studies and animal models that clarify the pathophysiological mechanisms are reviewed. Introduction Best vitelliform macular dystrophy (BVMD) is among the most frequently encountered autosomal dominant (AD) retinal dystrophies and predominantly affects the macula. BVMD was the first disease shown to be caused by mutations in the BEST1 gene, which encodes the bestrophin-1 protein that localizes to the retinal pigment epithelium (RPE) (Petrukhin et al., 1998). Subsequent studies showed that BEST1 gene mutations may also be found in patients with adult-onset foveomacular vitelliform dystrophy (AFVD) (Allikmets et al., 1999, Kramer et al., 2000, Seddon et al., 2001). BVMD and AFVD are related phenotypes with abnormalities that are generally restricted to the macula. However, more widespread ocular abnormalities may arise in association with specific BEST1 gene mutations that cause AD vitreoretinochoroidopathy (ADVIRC) and AD MRCS (microcornea, rod-cone dystrophy, early-onset cataract, and posterior staphyloma) syndrome (Reddy et al., 2003, Yardley et al., 2004, Michaelides et al., 2006, Burgess et al., 2008a). The same applies to autosomal recessive bestrophinopathy (ARB), the human null phenotype of bestrophin-1, which is associated with high hyperopia and shallow anterior chambers (Burgess et al., 2008b). Therefore, ADVIRC, MRCS syndrome, as well as ARB belong to a spectrum of diseases with abnormal ocular development that extends beyond the retina. In this paper, we aim to review the characteristics of the BEST1 gene and its multifunctional protein product bestrophin-1, with an emphasis on the broad spectrum of ocular phenotypes associated with mutations in this gene. The effects of different BEST1 mutations are discussed, as well as their genotype–phenotype correlations. Available in vitro and animal models are addressed, as well as histopathologic observations in BEST1 -related diseases, that expand our insight in the pathogenesis. Finally, perspectives on future therapeutic strategies are discussed. The BEST1 gene The human BEST1 gene was identified in 1998 by Petrukhin and colleagues (Petrukhin et al., 1998). BEST1 is located on chromosome 11q12, spans 15 kilobases of genomic DNA and contains 11 exons of which 10 are protein-coding (Marquardt et al., 1998, Petrukhin et al., 1998). Eight years later, the mouse ortholog was characterized (Kramer et al., 2004). An alternative name for BEST1 is VMD2 , but the Human Genome Organisation and the Mouse Genome Database nomenclature committees recently recommended Click here to read entire article References R.E. Andrade et al. Photodynamic therapy with verteporfin for subfoveal choroidal neovascularization in Best disease Am. J. Ophthalmol. (2003) B. Bakall et al. Enhanced accumulation of A2E in individuals homozygous or heterozygous for mutations in BEST1 (VMD2) Exp. Eye Res. (2007) R. Barro Soria et al. Bestrophin 1 and 2 are components of the Ca(2+) activated Cl(−) conductance in mouse airways Biochim. Biophys. Acta (2008) N. Benhamou et al. Adult-onset foveomacular vitelliform dystrophy: a study by optical coherence tomography Am. J. Ophthalmol. (2003) W.E. Benson et al. Best's vitelliform macular dystrophy Am. J. Ophthalmol. (1975) C.J.F. Boon et al. The spectrum of retinal dystrophies caused by mutations in the peripherin/RDS gene Prog. Retin. Eye Res. (2008) C.J.F. Boon et al. Fundus autofluorescence imaging of retinal dystrophies Vis. Res. (2008) C.J.F. Boon et al. Basal laminar drusen caused by compound heterozygous variants in the CFH gene Am. J. Hum. Genet. (2008) D.B. Burgess et al. Macular disease resembling adult foveomacular vitelliform dystrophy in older adults Ophthalmology (1987) R. Burgess et al. Biallelic mutation of BEST1 causes a distinct retinopathy in humans Am. J. Hum. Genet. (2008) G.M. Caldwell et al. Bestrophin gene mutations in patients with Best vitelliform macular dystrophy Genomics (1999) L. Cartegni et al. Determinants of exon 7 splicing in the spinal muscular atrophy genes, SMN1 and SMN2 Am. J. Hum. Genet. (2006) S.Y. Cohen et al. Monozygotic twin sisters with adult vitelliform macular dystrophy Am. J. Ophthalmol. (1993) J. Dillon et al. The photochemical oxidation of A2E results in the formation of a 5,8,5',8'-bis-furanoid oxide Exp. Eye Res. (2004) N. Esumi et al. Analysis of the VMD2 promoter and implication of E-box binding factors in its regulation J. Biol. Chem. (2004) N. Esumi et al. VMD2 promoter requires two proximal E-box sites for its activity in vivo and is regulated by the MITF-TFE family J. Biol. Chem. (2007) G.A. Fishman et al. Visual acuity in patients with Best vitelliform macular dystrophy Ophthalmology (1993) T. Furukawa et al. Crx , a novel otx-like homeobox gene, shows photoreceptor-specific expression and regulates photoreceptor differentiation Cell (1997) R.P. Gallemore et al. Retinal pigment epithelial transport mechanisms and their contributions to the electroretinogram Prog. Retin. Eye Res. (1997) M.F. Goldberg et al. Histopathologic study of autosomal dominant vitreoretinochoroidopathy. Peripheral annular pigmentary dystrophy of the retina Ophthalmology (1989) J.S. Adorante et al. Potassium-dependent volume regulation in retinal pigment epithelium is mediated by Na, K, Cl cotransport J. Gen. Physiol. (1990) J.J. Alexander et al. Adeno-associated viral vectors and the retina Adv. Exp. Med. Biol. (2008) R. Allikmets et al. Evaluation of the Best disease gene in patients with age-related macular degeneration and other maculopathies Hum. Genet. (1999) R.E. Andrade et al. Optical coherence tomography in choroidal neovascular membrane associated with Best's vitelliform dystrophy Acta Ophthalmol. Scand. (2002) S.L. Ang et al. A targeted mouse Otx2 mutation leads to severe defects in gastrulation and formation of axial mesoderm and to deletion of rostral brain Development (1996) M.A. Apushkin et al. Novel de novo mutation in a patient with Best macular dystrophy Arch. Ophthalmol. (2006) J.J. Arnold et al. Adult vitelliform macular degeneration: a clinicopathological study Eye (2003) L.O. Atchaneeyasakul et al. Mutation analysis of the VMD2 gene in Thai families with Best macular dystrophy Ophthalmic Genet. (2008) W. Baca et al. Dark adaptation in patients with Best vitelliform macular dystrophy Br. J. Ophthalmol. (1994) J.W. Bainbridge et al. Gene therapy progress and prospects: the eye Gene Ther. (2006) B. Bakall et al. The mutation spectrum of the bestrophin protein-functional implications Hum. Genet. (1999) B. Bakall et al. Expression and localization of bestrophin during normal mouse development Invest. Ophthalmol. Vis. Sci. (2003) B. Bakall et al. Bestrophin-2 is involved in the generation of intraocular pressure Invest. Ophthalmol. Vis. Sci. (2008) D.B. Barr et al. Autofluorescence in a patient with adult vitelliform degeneration Eur. J. Ophthalmol. (1995) R. Barro Soria et al. Bestrophin 1 enables Ca2+ activated Cl− conductance in epithelia J. Biol. Chem. (2006) M. Battaglia Parodi et al. Vascularized pigment epithelial detachment in adult-onset foveomacular vitelliform dystrophy Eur. J. Ophthalmol. (2000) M. Battaglia Parodi et al. Photodynamic therapy for choroidal neovascularization associated with pattern dystrophy Retina (2003) C. Baum et al. Mutagenesis and oncogenesis by chromosomal insertion of gene transfer vectors Hum. Gene Ther. (2006) F. Best Über eine hereditäre Maculaaffektion. Beitrag zur Vererbungslehre Z. Augenheilk (1905) S. Bialek et al. K+ and Cl− transport mechanisms in bovine pigment epithelium that could modulate subretinal space volume and composition J. Physiol. (1994) C.F. Blodi et al. Best's vitelliform dystrophy Ophthalmic Paediatr. Genet. (1990) L.H. Bloom et al. Adult vitelliform macular degeneration Br. J. Ophthalmol. (1981) C.J.F. Boon et al. Clinical and genetic heterogeneity in multifocal vitelliform dystrophy Arch. Ophthalmol. (2007) Boon, C.J.F., Theelen, T., Hoefsloot, E.H., van Schooneveld, M.J., Keunen, J.E.E., Cremers, F.P.M., Klevering, B.J.,... R. Brecher et al. Adult vitelliform macular dystrophy Eye (1990) N.M. Bressler et al. Natural course of poorly defined choroidal neovascularization associated with macular degeneration Arch. Ophthalmol. (1988) P.K. Buch et al. AAV-mediated gene therapy for retinal disorders: from mouse to man Gene Ther. (2008) K.M. Bumsted et al. Dorsal retinal pigment epithelium differentiates as neural retina in the microphthalmia (mi/mi) mouse Invest. Ophthalmol. Vis. Sci. (2000) R. Burgess et al. ADVIRC is caused by distinct mutations in BEST1 that alter pre-mRNA splicing J. Med. Genet. (2008) M. Caputi et al. A novel bipartite splicing enhancer modulates the differential processing of the human fibronectin EDA exon Nucleic Acids Res. (1994)

Isosomppi, J., Västinsalo, H., Geller, S. F., Heon, E., Flannery, J. G., & Sankila, E. M. | Molecular Vision | 2009 Sep 8 | Vol. 15 | pgs. 1806-18 | ncbi.nlm.nih.gov/pmc/articles/PMC2742642/ Abstract Purpose Mutations of clarin 1 ( CLRN1 ) cause Usher syndrome type 3 (USH3). To determine the effects of USH3 mutations on CLRN1 function, we examined the cellular distribution and stability of both normal and mutant CLRN1 in vitro. We also searched for novel disease-causing mutations in a cohort of 59 unrelated Canadian and Finnish USH patients. Methods Mutation screening was performed by DNA sequencing. For the functional studies, wild-type (WT) and mutant CLRN1 genes were expressed as hemagglutinin (HA) tagged fusion proteins by transient transfection of BHK-21 cells. Subcellular localization of CLRN1-HA was examined by confocal microscopy. The N-glycosylation status of CLRN1 was studied by using the N-glycosidase F (PNGase F) enzyme and western blotting. Cycloheximide treatment was used to assess the stability of CLRN1 protein. Results We found three previously reported pathogenic mutations, p.A123D, p.N48K, and p.Y176X, and a novel sequence variant, p.L54P, from the studied USH patients. The WT HA-tagged CLRN1 was correctly trafficked to the plasma membrane, whereas mutant CLRN1-HA proteins were mislocalized and retained in the endoplasmic reticulum. PNGase F treatment of CLRN1-HA resulted in an electrophoretic mobility shift consistent with sugar residue cleavage in WT and in all CLRN1 mutants except in p.N48K mutated CLRN1, in which the mutation abolishes the glycosylation site. Inhibition of protein expression with cycloheximide indicated that WT CLRN1-HA remained stable. In contrast, the CLRN1 mutants showed reduced stability. Conclusions WT CLRN1 is a glycoprotein localized to the plasma membrane in transfected BHK-21 cells. Mutant CLRN1 proteins are mislocalized. We suggest that part of the pathogenesis of USH3 may be associated with defective intracellular trafficking as well as decreased stability of mutant CLRN1 proteins. Introduction Usher syndrome (USH) describes a group of autosomal recessive diseases with bilateral sensorineural hearing loss and visual impairment phenotypically similar to retinitis pigmentosa (RP) [ 1 - 4 ]. Prevalence of USH in different populations is estimated to range from 3.5 to 6.2 per 100,000, thus making it the most frequent cause of combined deaf-blindness worldwide [ 5 ]. The condition has been classified into three clinical subtypes (USH1, USH2, and USH3), based on the severity and progression of the hearing impairment, presence or absence of vestibular dysfunction, and the age of onset of RP [ 1 ]. This classification remains in clinical use, although recent progress on the molecular genetics and clinical research of USH has revealed broad genetic and clinical heterogeneity [ 3 , 6 ]. Atypical forms of USH have been identified within all three clinical types, and there is considerable overlap of symptoms among the subtypes. A distinguishing feature of USH3 is the wide spectrum of nonlinear progressive hearing impairment, which ranges from a near normal to a severe audiometric phenotype [ 7 ]. USH3 patients may also have either normal or decreased vestibular responses [ 8 ]. The rate of visual loss in USH3 is similar to other USH subtypes [ 9 ], with the most recent analyses suggesting that retinal degeneration in USH3 progresses more rapidly than in USH2A [ 10 , 11 ]. The variable phenotype may cause USH3 to be under-diagnosed and it may be more prevalent than previously indicated [ 6 ]. To date, nine USH gene products have been identified: the molecular motor myosin VIIa (USH1B) [ 12 ]; the cell adhesion proteins cadherin 23 (USH1D) [ 13 ] and protocadherin 15 (USH1F) [ 14 , 15 ]; the scaffold proteins harmonin (USH1C) [ 16 ], SANS (USH1G) [ 17 ], and whirlin (USH2D) [ 18 ]; the G-protein-coupled 7-transmembrane receptor VLGR1b (USH2C) [ 19 ]; two isoforms of the extracellular matrix connected protein usherin (USH2A) [ 20 , 21 ]; and the four-pass transmembrane domain protein clarin 1 (USH3) [ 22 , 23 ]. There is growing evidence suggesting that these proteins form a network, which is critical for the development and maintenance of the sensorineural cells in the inner ear and the retina [ 3 , 4 , 24 - 28 ]. Click here to read original source article References Petit C. Usher syndrome: from genetics to pathogenesis. Annu Rev Genomics Hum Genet. 2001;2:271–97. doi: 10.1146/annurev.genom.2.1.271. Ahmed ZM, Riazuddin S, Wilcox ER. The molecular genetics of Usher syndrome. Clin Genet. 2003;63:431–44. doi: 10.1034/j.1399-0004.2003.00109.x. Reiners J, Nagel-Wolfrum K, Jurgens K, Marker T, Wolfrum U. Molecular basis of human Usher syndrome: deciphering the meshes of the Usher protein network provides insights into the pathomechanisms of the Usher disease. Exp Eye Res. 2006;83:97–119. doi: 10.1016/j.exer.2005.11.010. Kremer H, van Wijk E, Märker T, Wolfrum U, Roepman R. Usher syndrome: molecular links of pathogenesis, proteins and pathways. Hum Mol Genet. 2006;15:R262–70. doi: 10.1093/hmg/ddl205. Spandau UH, Rohrschneider K. Prevalence and geographical distribution of Usher syndrome in Germany. Graefes Arch Clin Exp Ophthalmol. 2002;240:495–8. doi: 10.1007/s00417-002-0485-8. Cohen M, Bitner-Glindzicz M, Luxon L. The changing face of Usher syndrome: clinical implications. Int J Audiol. 2007;46:82–93. doi: 10.1080/14992020600975279. Plantinga RF, Kleemola L, Huygen PL, Joensuu T, Sankila EM, Pennings RJ, Cremers CW. Serial audiometry and speech recognition findings in Finnish Usher syndrome type III patients. Audiol Neurootol. 2005;10:79–89. doi: 10.1159/000083363. Sadeghi M, Cohn ES, Kimberling WJ, Tranebjaerg L, Moller C. Audiological and vestibular features in affected subjects with USH3: a genotype/phenotype correlation. Int J Audiol. 2005;44:307–16. doi: 10.1080/14992020500060610. Pakarinen L, Tuppurainen K, Laippala P, Mantyjarvi M, Puhakka H. The ophthalmological course of Usher syndrome type III. Int Ophthalmol. 1995;19:307–11. doi: 10.1007/BF00130927. Plantinga RF, Pennings RJ, Huygen PL, Sankila EM, Tuppurainen K, Kleemola L, Cremers CW, Deutman AF. Visual impairment in Finnish Usher syndrome type III. Acta Ophthalmol Scand. 2006;84:36–41. doi: 10.1111/j.1600-0420.2005.00507. Herrera W, Aleman TS, Cideciyan AV, Roman AJ, Banin E, Ben-Yosef T, Gardner LM, Sumaroka A, Windsor EA, Schwartz SB, Stone EM, Liu XZ, Kimberling WJ, Jacobson SG. Retinal disease in Usher syndrome III caused by mutations in the clarin-1 gene. Invest Ophthalmol Vis Sci. 2008;49:2651–60. doi: 10.1167/iovs.07-1505. Weil D, Blanchard S, Kaplan J, Guilford P, Gibson F, Walsh J, Mburu P, Varela A, Levilliers J, Weston MD, Kelley PM, Kimberling WJ, Levi-Acobas MWF, Larget-Piet D, Munnich A, Steel KP, Brown SDM, Petit C. Defective myosin VIIA gene responsible for Usher syndrome type 1B. Nature. 1995;374:60–1. doi: 10.1038/374060a0. Bolz H, von Brederlow B, Ramírez A, Bryda EC, Kutsche K, Nothwang HG, Seeliger M. del C-Salcedó Cabrera M, Vila MC, Molina OP, Gal A, Kubisch C. Mutation of CDH23, encoding a new member of the cadherin gene family, causes Usher syndrome type 1D. Nat Genet. 2001;27:108–12. doi: 10.1038/83667. Ahmed ZM, Riazuddin S, Bernstein SL, Ahmed Z, Khan S, Griffith AJ, Morell RJ, Friedman TB, Riazuddin S, Wilcox ER. Mutations of the protocadherin gene PCDH15 cause Usher syndrome type 1F. Am J Hum Genet. 2001;69:25–34. doi: 10.1086/321277. Alagramam KN, Yuan H, Kuehn MH, Murcia CL, Wayne S, Srisailpathy CR, Lowry RB, Knaus R, Van Laer L, Bernier FP, Schwartz S, Lee C, Morton CC, Mullins RF, Ramesh A, Van Camp G, Hageman GS, Woychik RP, Smith RJ. Mutations in the novel protocadherin PCDH15 cause Usher syndrome type 1F. Hum Mol Genet. 2001;10:1709–18. doi: 10.1093/hmg/10.16.1709. Verpy E, Leibovici M, Zwaenepoel I, Liu XZ, Gal A, Salem N, Mansour A, Blanchard S, Kobayashi I, Keats BJ, Slim R, Petit C. A defect in harmonin, a PDZ domain-containing protein expressed in the inner ear sensory hair cells, underlies Usher syndrome type 1C. Nat Genet. 2000;26:51–5. doi: 10.1038/79171. Weil D, El-Amraoui A, Masmoudi S, Mustapha M, Kikkawa Y, Lainé S, Delmaghani S, Adato A, Nadifi S, Zina ZB, Hamel C, Gal A, Ayadi H, Yonekawa H, Petit C. Usher syndrome type I G (USH1G) is caused by mutations in the gene encoding SANS, a protein that associates with the USH1C protein, harmonin. Hum Mol Genet. 2003;12:463–71. doi: 10.1093/hmg/ddg051. Ebermann I, Scholl HP, Charbel Issa P, Becirovic E, Lamprecht J, Jurklies B, Millán JM, Aller E, Mitter D, Bolz H. A novel gene for Usher syndrome type 2: mutations in the long isoform of whirlin are associated with retinitis pigmentosa and sensorineural hearing loss. Hum Genet. 2007;121:203–11. doi: 10.1007/s00439-006-0304-0. Weston MD, Luijendijk MW, Humphrey KD, Moller C, Kimberling WJ. Mutations in the VLGR1 gene implicate G-protein signaling in the pathogenesis of Usher syndrome type II. Am J Hum Genet. 2004;74:357–66. doi: 10.1086/381685. Eudy JD, Yao S, Weston MD, Ma-Edmonds M, Talmadge CB, Cheng JJ, Kimberling WJ, Sumegi J. Isolation of a gene encoding a novel member of the nuclear receptor superfamily from the critical region of Usher syndrome type IIa at 1q41. Genomics. 1998;50:382–4. doi: 10.1006/geno.1998.5345. van Wijk E, Pennings RJ, te Brinke H, Claassen A, Yntema HG, Hoefsloot LH, Cremers FP, Cremers CW, Kremer H. Identification of 51 novel exons of the Usher syndrome type 2A (USH2A) gene that encode multiple conserved functional domains and that are mutated in patients with Usher syndrome type II. Am J Hum Genet. 2004;74:738–44. doi: 10.1086/383096. Joensuu T, Hämäläinen R, Yuan B, Johnson C, Tegelberg S, Gasparini P, Zelante L, Pirvola U, Pakarinen L, Lehesjoki AE, de la Chapelle A, Sankila EM. Mutations in a novel gene with transmembrane domains underlie Usher syndrome type 3. Am J Hum Genet. 2001;69:673–84. doi: 10.1086/323610. Adato A, Vreugde S, Joensuu T, Avidan N, Hamalainen R, Belenkiy O, Olender T, Bonne-Tamir B, Ben-Asher E, Espinos C, Millán JM, Lehesjoki AE, Flannery JG, Avraham KB, Pietrokovski S, Sankila EM, Beckmann JS, Lancet D. USH3A transcripts encode clarin-1, a four-transmembrane-domain protein with a possible role in sensory synapses. Eur J Hum Genet. 2002;10:339–50. doi: 10.1038/sj.ejhg.5200831. El-Amraoui A, Petit C. Usher I syndrome: unravelling the mechanisms that underlie the cohesion of the growing hair bundle in inner ear sensory cells. J Cell Sci. 2005;118:4593–603. doi: 10.1242/jcs.02636. Reiners J, van Wijk E, Märker T, Zimmermann U, Jürgens K, te Brinke H, Overlack N, Roepman R, Knipper M, Kremer H, Wolfrum U. Scaffold protein harmonin (USH1C) provides molecular links between Usher syndrome type 1 and type 2. Hum Mol Genet. 2005;14:3933–43. doi: 10.1093/hmg/ddi417. Adato A, Michel V, Kikkawa Y, Reiners J, Alagramam KN, Weil D, Yonekawa H, Wolfrum U, El-Amraoui A, Petit C. Interactions in the network of Usher syndrome type 1 proteins. Hum Mol Genet. 2005;14:347–56. doi: 10.1093/hmg/ddi031. Maerker T, van Wijk E, Overlack N, Kersten FF, McGee J, Goldmann T, Sehn E, Roepman R, Walsh EJ, Kremer H, Wolfrum U. A novel Usher protein network at the periciliary reloading point between molecular transport machineries in vertebrate photoreceptor cells. Hum Mol Genet. 2008;17:71–86. doi: 10.1093/hmg/ddm285. Tian G, Zhou Y, Hajkova D, Miyagi M, Dinculescu A, Hauswirth WW, Palczewski K, Geng R, Alagramam KN, Isosomppi J, Sankila EM, Flannery JG, Imanishi Y. Clarin-1, encoded by the Usher syndrome III causative gene, forms a membranous microdomain: possible role of clarin-1 in organizing the actin cytoskeleton. J Biol Chem. 2009;284:18980–93. doi: 10.1074/jbc.M109.003160.

Hiroyuki Morimura , Gerald A. Fishman, Sandeep A. Grover, Anne B. Fulton, Eliot L. Berson, Thaddeus P. Dryja |   PNAS | 17 May 1998 | Vol. 95 (6) | pgs. 3088–3093 | doi:  10.1073/pnas.95.6.3088 Abstract RPE65 is a protein of unknown function expressed specifically by the retinal pigment epithelium. We examined all 14 exons of this gene in 147 unrelated patients with autosomal recessive retinitis pigmentosa (RP), in 15 patients with isolate RP, and in 45 patients with Leber congenital amaurosis (LCA). Sequence anomalies that were likely to be pathogenic were found in two patients with recessive RP, in one patient with isolate RP recategorized as recessive, and in seven patients with LCA. Cosegregation analysis in each available family showed that all affected individuals were either homozygotes or compound heterozygotes and that all unaffected individuals were either heterozygote carriers or homozygous wild type. In one family, there was one instance of a new mutation not present in either parent of the affected individual. In another family, affected members with recessive RP in three branches (i.e., three distinct pairs of parents) were compound heterozygotes for the same two mutations or homozygous for one of them. Based on our results, mutations in the RPE65 gene appear to account for ≈2% of cases of recessive RP and ≈16% of cases of LCA. Over 40 loci for human hereditary retinal degenerations involving the photoreceptors and retinal pigment epithelium are known ( http://utsph.sph.uth.tmc.edu/www/utsph/RetNet/home.htm ). Most of these loci are unidentified genes that have been recognized by linkage studies alone. Our group is engaged in identifying genes responsible for this set of diseases primarily through a candidate gene-based approach ( 1 ). In this report, we describe an analysis of the RPE65 gene, which has been assigned to chromosome 1p31 ( 2 ). This gene was discovered through its protein product that forms a complex with an antibody raised against human retinal pigment epithelium ( 3 ). The cDNA sequence predicts a protein with 533 amino acid residues and a molecular mass of ≈61 kDa ( 4 ). The protein is associated with the endoplasmic reticulum of the retinal pigment epithelium in vertebrates ( 3 , 5 ). Although the biochemical function of the protein product is currently obscure, the tissue-specific expression of the RPE65 gene made it an attractive candidate as a cause for some retinal degenerations because the retinal pigment epithelium has an essential role in maintaining the viability of the neighboring photoreceptor cells. In particular, enzymes in the endoplasmic reticulum are responsible for the recycling of the chromophore used by photoreceptor opsins. To explore the possible role that defects in RPE65 might play in the etiology of retinal degenerations, we screened a large cohort of unrelated patients with retinitis pigmentosa or Leber congenital amaurosis for mutations. Because RPE65 is expressed specifically in the eye, the study focused on patients with nonsyndromic forms of these diseases. This study was carried out contemporaneously with studies from two other groups that recently have been published ( 6 , 7 ) . Click here to read entire article References Dryja T P. Proc Natl Acad Sci USA. 1997;94:12117–12121. doi: 10.1073/pnas.94.22.12117. Hamel C P, Jenkins N A, Gilbert D J, Copeland N G, Redmond T M. Genomics. 1994;20:509–512. doi: 10.1006/geno.1994.1212. Hamel C P, Tsilou E, Harris E, Pfeffer B A, Hooks J J, Detrick B, Redmond T M. J Neurosci Res. 1993;34:414–425. doi: 10.1002/jnr.490340406. Hamel C P, Tsilou E, Pfeffer B A, Hooks J J, Detrick B, Redmond T M. J Biol Chem. 1993;268:15751–15757. Nicoletti A, Wong D J, Kawase K, Gibson L H, Yang-Feng T L, Richards J E, Thompson D A. Hum Mol Genet. 1995;4:641–649. doi: 10.1093/hmg/4.4.641. Marlhens F, Bareil C, Griffoin J M, Zrenner E, Amalric P, Eliaou C, Liu S Y, Harris E, Redmond T M, Arnaud B, et al. Nat Genet. 1997;17:139–141. doi: 10.1038/ng1097-139. Gu S M, Thompson D A, Srikumari C R S, Lorenz B, Finckh U, Nicoletti A, Murthy K R, Rathmann M, Kumaramanickavel G, Denton M J, et al. Nat Genet. 1997;17:194–197. doi: 10.1038/ng1097-194.

Lina Zelinger , Eyal Banin, Alexey Obolensky, Liliana Mizrahi-Meissonnier, Avigail Beryozkin, Dikla Bandah-Rozenfeld, Shahar Frenkel, Tamar Ben-Yosef, Saul Merin,  Sharon B. Schwartz ,  Artur V. Cideciyan , Samuel G. Jacobson, Dror Sharon |   American Society of Human Genetics (AJHG) |  2011 Feb 11 | 88(2) | 207–215 |  doi: 10.1016/j.ajhg.2011.01.002 Abstract Retinitis pigmentosa (RP) is a heterogeneous group of inherited retinal degenerations caused by mutations in at least 50 genes. Using homozygosity mapping in Ashkenazi Jewish (AJ) patients with autosomal-recessive RP (arRP), we identified a shared 1.7 Mb homozygous region on chromosome 1p36.11. Sequence analysis revealed a founder homozygous missense mutation, c.124A>G (p.Lys42Glu), in the dehydrodolichyl diphosphate synthase gene ( DHDDS ) in 20 AJ patients with RP of 15 unrelated families. The mutation was not identified in an additional set of 109 AJ patients with RP, in 20 AJ patients with other inherited retinal diseases, or in 70 patients with retinal degeneration of other ethnic origins. The mutation was found heterozygously in 1 out of 322 ethnically matched normal control individuals. RT-PCR analysis in 21 human tissues revealed ubiquitous expression of DHDDS . Immunohistochemical analysis of the human retina with anti-DHDDS antibodies revealed intense labeling of the cone and rod photoreceptor inner segments. Clinical manifestations of patients who are homozygous for the c.124A>G mutation were within the spectrum associated with arRP. Most patients had symptoms of night and peripheral vision loss, nondetectable electroretinographic responses, constriction of visual fields, and funduscopic hallmarks of retinal degeneration. DHDDS is a key enzyme in the pathway of dolichol, which plays an important role in N -glycosylation of many glycoproteins, including rhodopsin. Our results support a pivotal role of DHDDS in retinal function and may allow for new therapeutic interventions for RP. Main Text Retinitis pigmentosa (RP; MIM 268000 ) is the most common inherited retinal degeneration, with an estimated worldwide prevalence of 1:4000. 1–3 The disease is highly heterogeneous and has several patterns of inheritance. At present, 35 genetic loci have been implicated in nonsyndromic autosomal-recessive RP (arRP), most of which account for a few percent of RP cases each. Although many of the early identified arRP genes were excellent candidates for the disease when mutated, mainly because of the function of the encoded protein (e.g., PDE6A 4 [MIM 180071 ] and PDE6B 5 [MIM 180072 ]), a large proportion of the recently identified genes were not a priori considered as candidates and were identified through whole-genome linkage or homozygosity mapping followed by mutation screening of a large number of genes in the linked intervals (e.g., EYS 6 [MIM 612424 ] and SPATA7 7 [MIM 609868 ]). Through those studies, a new class of genes encoding proteins with housekeeping-like function (e.g., IDH3B [MIM 604526 ] for arRP 8 and splicing factors for autosomal-dominant RP 9,10 ) have been identified and provided new insight into processes that result in retinal degeneration. The reason for the retina-specific phenotype caused by mutations in these genes is still unclear. The Ashkenazi Jewish (AJ) population was established by Jews who originated in the Middle East and migrated to Europe, initially settling in Germany (the “Ashkenaz” region) at or before the 4 th century. The AJ lived in closed communities in European countries and developed a unique culture and language (named Yiddish, which is based on a few different languages, including German, Hebrew, and Aramaic). After the Holocaust, the population size dropped from about 8.8 million individuals to only 2.8 million, and AJ immigrated out of Europe, mainly to the United States and the emerging state of Israel. AJ currently constitute the largest Jewish ethnic group in both countries. A large amount of effort was directed to study the genetic structure of the AJ population, in the context of other Jewish ethnic groups and Middle Eastern populations, at the Y chromosome, 11,12 mitochondrial, 13 and genomic 14,15 levels. Although consanguineous marriages are relatively uncommon among AJ (1.5% and rapidly declining), 16,17 most individuals who are affected by a rare AR disease in this ethnic group are homozygous for the disease-causing mutation, mainly because of a high rate of intracommunity marriages. 17 Therefore, genetic analysis of hereditary diseases in the AJ population, via homozygosity mapping, can be highly efficient. To read entire article, click here

Bernardo V Alvarez, Eranga N Vithana, Zhenglin Yang, Adrian H Koh, Kit Yeung, Victor Yong, Haley J Shandro, Yali Chen, Prasanna Kolatkar, Paaventhan Palasingam, Kang Zhang, Tin Aung, Joseph R Casey | Investigative Ophthalmology & Visual Science  | Aug 2007 | Vol.48 | 3459-3468 | doi.org/10.1167/iovs.06-1515 Abstract Purpose The autosomal dominant retinitis pigmentosa (adRP) gene on chromosome 17, region q22 (RP17), was recently identified as a glycosylphosphatidylinositol membrane-anchored zinc metalloenzyme (protein CAIV), highly expressed in the choriocapillaris of the eye and undetectable in the retina. Only two missense mutations have thus far been identified in the gene CA4 . Functional analysis of these mutations demonstrated that retinal disease may result from perturbation of pH homeostasis in the outer retina, after disruption of CAIV and sodium bicarbonate cotransporter 1 (NBC1)–mediated bicarbonate transport. CA4 was screened in a panel of patients with RP, to expand the mutation spectrum of this novel adRP gene and understand its pathogenic mechanism. Methods A total of 96 patients with simplex RP and adRP of Chinese ethnicity were screened for mutations in the eight coding exons of the CA4 gene by bidirectional sequencing. Functional consequences of CA4 mutations on the NBC1-mediated bicarbonate transport were studied by measuring bicarbonate fluxes in HEK293 cells cotransfected with NBC1 and CA4 mutant cDNAs. Results Thirteen sequence alterations were identified, including a novel mutation within exon 3 of CA4 (R69H) in a patient with simplex RP. R69H was not found in 432 normal chromosomes. R69H CAIV impaired NBC1-mediated pH recovery after acid load. Conclusions A novel mutation has been identified in CA4 that provides further evidence that impaired pH regulation may underlie photoreceptor degeneration in RP17. This study indicates that, as with European patients with RP, mutations in CA4 also account for ≤1% of Chinese patients with RP. Click here to read original article

Aisha Pandor, Rajkumar Ramesar, Sharon Prince | J Cell Biochem ​ | 2010 Oct 15 | Vol. 111, Issue 3 | 735-41 |  doi: 10.1002/jcb.22759 Abstract Retinitis pigmentosa is a highly heterogeneous form of inherited blindness which affects more than 1.3 million individuals worldwide. The RP17 form of the disease is caused by an arginine to tryptophan (R14W) mutation in the signal sequence of carbonic anhydrase IV (CAIV). While CAIV is expressed in the choriocapillaries of the eye and renal epithelium, the R14W mutation results in an exclusively ocular phenotype in affected individuals. In order to investigate the mechanism of disease in RP17 and the lack of kidney phenotype, we compared the subcellular localization and post-translational processing of wild-type (WT)- and mutant-CAIV in three cell types. We show using immunocytochemistry that unlike WT CAIV which is transported to the plasma membrane of transfected COS-7 and HT-1080 cells, the R14W mutant CAIV is retained in the endoplasmic reticulum. Western blot analyses further reveal that whereas the WT CAIV is processed to its mature form in both these cell lines, significant levels of the R14W mutant protein remain in its immature form. Importantly, flow cytometry experiments demonstrate that compared to WT CAIV protein, expression of specifically the R14W CAIV results in an S and G2/M cell-cycle block, followed by apoptosis. Interestingly, when the above experiments were repeated in the human embryonic kidney cell line, HEK-293, strikingly different results were obtained. These cells were unaffected by the expression of the R14W mutant CAIV and were able to process the mutant and WT protein equally effectively. This study has important implications for our understanding of the RP17 phenotype. To read full text, click here

Muhammad Imran Khan, Ferry Kersten, Maleeha Azam, Rob Collin, Alamdar Hussain, Syed Tahir-A Shah, Jan Keunen, Hannie Kremer, Frans Cremers, Raheel Qamar, Anneke den Hollander |  Ophthalmology​ | 2011 Jul 1 | Vol.18, Issue 7 |1444-8 | doi: 10.1016/j.ophtha.2010.10.047    Objective: To describe the mutations in the CLRN1 gene in patients from 2 consanguineous Pakistani families diagnosed with autosomal recessive retinitis pigmentosa (arRP). Participants: Affected and unaffected individuals of 2 consanguineous Pakistani families and 90 unaffected controls from the same population. Informed consent was obtained from participants and the protocol was approved by a local institutional review board.