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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.

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. 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S P Daiger ,  L S Sullivan ,  S J Bowne | Clinical Genetics | 23 May 2013 | Volume 84, Issue 2 | Pages 132-141 | doi.org/10.1111/cge.12203 Abstract Retinitis pigmentosa (RP) is a heterogeneous set of inherited retinopathies with many disease-causing genes, many known mutations, and highly varied clinical consequences. Progress in finding treatments is dependent on determining the genes and mutations causing these diseases, which includes both gene discovery and mutation screening in affected individuals and families. Despite the complexity, substantial progress has been made in finding RP genes and mutations. Depending on the type of RP, and the technology used, it is possible to detect mutations in 30-80% of cases. One of the most powerful approaches to genetic testing is high-throughput 'deep sequencing', that is, next-generation sequencing (NGS). NGS has identified several novel RP genes but a substantial fraction of previously unsolved cases have mutations in genes that are known causes of retinal disease but not necessarily RP. Apparent discrepancy between the molecular defect and clinical findings may warrant reevaluation of patients and families. In this review, we summarize the current approaches to gene discovery and mutation detection for RP, and indicate pitfalls and unsolved problems. Similar considerations apply to other forms of inherited retinal disease. To purchase the publication, click here

Melissa C. Humbert, Katie Weihbrecht, Charles C. Searby, Yalan Li, Robert M. Pope, Val C. Sheffield, Seongjin Seo | Proceedings of the National Academy of Sciences of the United States of America (PNAS) | 27 Nov 2012 | 109 (48) | 19691-19696 | doi.org/10.1073/pnas.1210916109 Abstract Mutations affecting ciliary components cause a series of related genetic disorders in humans, including nephronophthisis (NPHP), Joubert syndrome (JBTS), Meckel-Gruber syndrome (MKS), and Bardet-Biedl syndrome (BBS), which are collectively termed "ciliopathies." Recent protein-protein interaction studies combined with genetic analyses revealed that ciliopathy-related proteins form several functional networks/modules that build and maintain the primary cilium. However, the precise function of many ciliopathy-related proteins and the mechanisms by which these proteins are targeted to primary cilia are still not well understood. Here, we describe a protein-protein interaction network of inositol polyphosphate-5-phosphatase E (INPP5E), a prenylated protein associated with JBTS, and its ciliary targeting mechanisms. INPP5E is targeted to the primary cilium through a motif near the C terminus and prenyl-binding protein phosphodiesterase 6D (PDE6D) -dependent mechanisms. Ciliary targeting of INPP5E is facilitated by another JBTS protein, ADP-ribosylation factor-like 13B (ARL13B), but not by ARL2 or ARL3. ARL13B missense mutations that cause JBTS in humans disrupt the ARL13B-INPP5E interaction. We further demonstrate interactions of INPP5E with several ciliary and centrosomal proteins, including a recently identified ciliopathy protein centrosomal protein 164 (CEP164). These findings indicate that ARL13B, INPP5E, PDE6D, and CEP164 form a distinct functional network that is involved in JBTS and NPHP but independent of the ones previously defined by NPHP and MKS proteins. Primary cilia are microtubule-based cell surface projections that emanate from the centrosome. This subcellular organelle functions as an antenna, sensing and transducing extracellular signals into the cell, and plays an essential role in regulating multiple cellular processes including the cell cycle, embryonic development, and tissue homeostasis ( 1 – 3 ). Mutations affecting ciliary and centrosomal components underlie a group of related human disorders such as Joubert syndrome (JBTS), Meckel-Gruber syndrome (MKS), nephronophthisis (NPHP), and Bardet-Biedl syndrome (BBS), collectively termed ciliopathies ( 1 – 3 ). Recent protein–protein interaction studies have identified several functional modules or networks involved in these ciliopathies ( 4 ). For example, BBS proteins and intraflagellar transport (IFT) proteins form multiprotein complexes, the BBSome and the IFT complexes, respectively, and these complexes are involved in transporting ciliary proteins. Likewise, NPHP and MKS proteins form a distinct modular complex at the transition zone of primary cilia and regulate ciliary membrane compositions ( 5 – 9 ). However, there are many ciliary and centrosomal proteins [e.g., inositol polyphosphate-5-phosphatase E (INPP5E) and ADP-ribosylation factor-like 13B (ARL13B)] that have not been linked to any of the known functional networks and their precise functions remain to be elucidated. INPP5E encodes an enzyme that hydrolyzes the 5-phosphate of PtdIns(3,4,5)P3 and PtdIns(4,5)P2 and localizes to primary cilia. Mutations in this gene cause JBTS in humans ( 10 , 11 ). In mice, loss of Inpp5e activity results in cystic kidney, bilateral anophthalmia, polydactyly, skeletal defects, cleft palate, and cerebral developmental defects ( 11 ). Inactivation of Inpp5e in adult mice results in obesity and photoreceptor degeneration. Interestingly, many proteins that localize to cilia, including INPP5E, RPGR, PDE6 α and β subunits, GRK1 (Rhodopsin kinase), and GNGT1 (Transducin γ chain), are prenylated (either farnesylated or geranylgeranylated), and mutations in these genes or genes involved in their prenylation (e.g., AIPL1 and RCE1 ) lead to photoreceptor degeneration in vertebrates and humans ( 12 – 18 ). Understanding the molecular mechanisms by which prenylated proteins are transported to primary cilia would have significant ramifications in developing therapeutic strategies to treat blindness and other ciliopathy phenotypes associated with these genes. In this study, we sought to determine the functional network of INPP5E and the mechanisms by which INPP5E is targeted to primary cilia. We determined the ciliary targeting sequence (CTS) of INPP5E, the small GTPase responsible for its ciliary targeting, and an interaction network that connects INPP5E to other known ciliopathy genes and new candidates. To read entire article, click here Reference Goetz SC, Anderson KV. The primary cilium: A signalling centre during vertebrate development. Nat Rev Genet. 2010;11(5):331–344. doi: 10.1038/nrg2774. Singla V, Reiter JF. The primary cilium as the cell’s antenna: Signaling at a sensory organelle. Science. 2006;313(5787):629–633. doi: 10.1126/science.1124534. Mockel A, et al. Retinal dystrophy in Bardet-Biedl syndrome and related syndromic ciliopathies. Prog Retin Eye Res. 2011;30(4):258–274. doi: 10.1016/j.preteyeres.2011.03.001. van Reeuwijk J, Arts HH, Roepman R. Scrutinizing ciliopathies by unraveling ciliary interaction networks. Hum Mol Genet. 2011;20(R2):R149–R157. doi: 10.1093/hmg/ddr354. Williams CL, et al. MKS and NPHP modules cooperate to establish basal body/transition zone membrane associations and ciliary gate function during ciliogenesis. J Cell Biol. 2011;192(6):1023–1041. doi: 10.1083/jcb.201012116. Craige B, et al. 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Lori S Sullivan ,  Daniel C Koboldt ,  Sara J Bowne ,  Steven Lang ,  Susan H Blanton ,  Elizabeth Cadena ,  Cheryl E Avery , Richard A Lewis ,  Kaylie Webb-Jones ,  Dianna H Wheaton ,  David G Birch ,  Razck Coussa ,  Huanan Ren ,  Irma Lopez , Christina Chakarova ,  Robert K Koenekoop ,  Charles A Garcia ,  Robert S Fulton ,  Richard K Wilson ,   George M Weinstock ,  Stephen P Daig er | Investiga tive Ophthalmology & Visual Science | 2014 Sep 4 | 55 (11) | Pgs. 7147-58 | doi: 10.1167/iovs.14-15419 Abstract Purpose: To identify the cause of retinitis pigmentosa (RP) in UTAD003, a large, six-generation Louisiana family with autosomal dominant retinitis pigmentosa (adRP). Methods: A series of strategies, including candidate gene screening, linkage exclusion, genome-wide linkage mapping, and whole-exome next-generation sequencing, was used to identify a mutation in a novel disease gene on chromosome 10q22.1. Probands from an additional 404 retinal degeneration families were subsequently screened for mutations in this gene. Results: Exome sequencing in UTAD003 led to identification of a single, novel coding variant (c.2539G>A, p.Glu847Lys) in hexokinase 1 (HK1) present in all affected individuals and absent from normal controls. One affected family member carries two copies of the mutation and has an unusually severe form of disease, consistent with homozygosity for this mutation. Screening of additional adRP probands identified four other families (American, Canadian, and Sicilian) with the same mutation and a similar range of phenotypes. The families share a rare 450-kilobase haplotype containing the mutation, suggesting a founder mutation among otherwise unrelated families. Conclusions: We identified an HK1 mutation in five adRP families. Hexokinase 1 catalyzes phosphorylation of glucose to glucose-6-phosphate. HK1 is expressed in retina, with two abundant isoforms expressed at similar levels. The Glu847Lys mutation is located at a highly conserved position in the protein, outside the catalytic domains. We hypothesize that the effect of this mutation is limited to the retina, as no systemic abnormalities in glycolysis were detected. Prevalence of the HK1 mutation in our cohort of RP families is 1%. Introduction Retinitis pigmentosa (RP) is a group of inherited dystrophic disorders of the retina leading to profound loss of vision or blindness. The clinical hallmarks of RP are night blindness, followed by progressive loss of peripheral vision, often culminating in complete blindness. Clinical findings of RP include “bone spicule” pigmentary deposits, retinal vessel attenuation, and characteristic changes in the electroretinograms (ERG). 1   Retinitis pigmentosa affects approximately 1 in 4000 people in the United States, Europe, and Japan. Retinitis pigmentosa is exceptionally heterogeneous with many different genes implicated, many different disease-causing mutations in each gene, and varying clinical presentations even among members of the same family. 2 For nonsyndromic RP, mutations in 24 genes are known to cause autosomal dominant RP (adRP); 45 genes cause recessive RP (arRP), and 3 genes cause X-linked RP (summarized in RetNet, https://sph.uth.edu/retnet/ [in the public domain]) .  The genes found to date as causes of adRP do not fall into a single functional category but include a diverse range of retinal functions, including components of the phototransduction cycle ( RHO , GUCA1A , RDH12 ); pre-mRNA processing factors ( PRPF3 , PRPF4 , PRPF6 , PRPF8 , PRPF31 , SNRNP200 ); structural proteins ( PRPH2 , ROM1 ); ciliary proteins ( RP1 , TOPORS ); transcription factors ( NRL , CRX , NR2E3 ); and a seemingly random assortment of other genes ( BEST1 , CA4 , FSCN2 , IMPDH1 , KLHL7 , RPE65 , SEMA4A ). With current techniques, we can identify likely disease-causing mutations in approximately 75% of patients with adRP (Daiger SP, manuscript in preparation, 2014). While mutations in some known genes may be missed, a number of additional adRP genes remain to be identified. In our University of Texas (UT) adRP cohort, mutations have been found in 205 of 265 families, leaving 60 (23%) with potentially novel adRP genes.  Click here to read entire article References Heckenlively JR. Retinitis Pigmentosa . London: J.B. Lippincott; 1988. Daiger SP. Identifying retinal disease genes: how far have we come, how far do we have to go? Novartis Found Symp . 2004; 255: 17–27, discussion 27–36, 177–178. Sullivan LS Bowne SJ Birch DG Prevalence of disease-causing mutations in families with autosomal dominant retinitis pigmentosa: a screen of known genes in 200 families. Invest Ophthalmol Vis Sci . 2006; 47: 3052–3064. Churchill JD Bowne SJ Sullivan LS Mutations in the X-linked retinitis pigmentosa genes RPGR and RP2 found in 8.5% of families with a provisional diagnosis of autosomal dominant retinitis pigmentosa. Invest Ophthalmol Vis Sci . 2013; 54: 1411–1416. Bowne SJ Sullivan LS Avery CE Mutations in the small nuclear riboprotein 200 kDa gene (SNRNP200) cause 1.6% of autosomal dominant retinitis pigmentosa. Mol Vis . 2013; 19: 2407–2417. Bowne SJ Sullivan LS Mortimer SE Spectrum and frequency of mutations in IMPDH1 associated with autosomal dominant retinitis pigmentosa and Leber congenital amaurosis. Invest Ophthalmol Vis Sci . 2006; 47: 34–42. Sullivan LS Bowne SJ Reeves MJ Prevalence of mutations in eyeGENE probands with a diagnosis of autosomal dominant retinitis pigmentosa. Invest Ophthalmol Vis Sci . 2013; 54: 6255–6261. Sullivan LS Bowne SJ Seaman CR Genomic rearrangements of the PRPF31 gene account for 2.5% of autosomal dominant retinitis pigmentosa. Invest Ophthalmol Vis Sci . 2006; 47: 4579–4588. Gire AI Sullivan LS Bowne SJ The Gly56Arg mutation in NR2E3 accounts for 1-2% of autosomal dominant retinitis pigmentosa. Mol Vis . 2007; 13: 1970–1975. Bowne SJ Sullivan LS Gire AI Mutations in the TOPORS gene cause 1% of autosomal dominant retinitis pigmentosa. Mol Vis . 2008; 14: 922–927. Click here to see all references