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and underlies severe Usher syndrome on the Arabian Peninsula Arif O. Khan, Elvir Becirovic, Christian Betz, Christine Neuhaus, Janine Altmüller, Lisa Maria Riedmayr, Susanne Motameny, Gudrun Nürnberg, Peter Nürnberg & Hanno J. Bolz | Scientific Reports | Vol. 7, Article # 1411 | 2017 May 03 | Abstract Deafblindness is mostly due to Usher syndrome caused by recessive mutations in the known genes. Mutation-negative patients therefore either have distinct diseases, mutations in yet unknown Usher genes or in extra-exonic parts of the known genes – to date a largely unexplored possibility. In a consanguineous Saudi family segregating Usher syndrome type 1 (USH1), NGS of genes for Usher syndrome, deafness and retinal dystrophy and subsequent whole-exome sequencing each failed to identify a mutation. Genome-wide linkage analysis revealed two small candidate regions on chromosome 3, one containing the USH3A gene CLRN1, which has never been associated with Usher syndrome in Saudi Arabia. Whole-genome sequencing (WGS) identified a homozygous deep intronic mutation, c.254–649T > G, predicted to generate a novel donor splice site. CLRN1 minigene-based analysis confirmed the splicing of an aberrant exon due to usage of this novel motif, resulting in a frameshift and a premature termination codon. We identified this mutation in an additional two of seven unrelated mutation-negative Saudi USH1 patients. Locus-specific markers indicated that c.254–649T > G CLRN1 represents a founder allele that may significantly contribute to deafblindness in this population. Our finding underlines the potential of WGS to uncover atypically localized, hidden mutations in patients who lack exonic mutations in the known disease genes. Introduction Usher syndrome is the most common cause of inherited deafblindness1. Type 1 (USH1) is characterized by congenital deafness and early (first decade) retinitis pigmentosa (RP), whereas type 2 (USH2) displays progressive hearing impairment and RP of later onset. USH3 is characterized by progressive hearing loss, RP, and variable peripheral vestibular dysfunction2. However, disease resulting from mutations in the USH3A gene, CLRN1, is variable, ranging from non-syndromic RP3 to USH14. The advent of next-generation sequencing (NGS) has enabled panel-sequencing of the 11 known Usher genes, and its application in a recent study on European deafblind patients identified the causative mutations in the majority5. In a Saudi Arabian family with four siblings affected by Usher syndrome type 1, escalating the genetic investigations from gene panel NGS over genome-wide linkage analysis to whole-exome sequencing (WES) and finally whole-genome sequencing (WGS) led up to the molecular diagnosis. Our study demonstrates the potential of WGS to unlock hidden mutations. Results NGS of gene panels for retinal dystrophy and for deafness Apart from a heterozygous frameshift mutation in TUBGCP6, c.5001_5003delinsCA (p.Gln1667Hisfs*11), NGS of the known genes for Usher syndrome, for other syndromic and isolated hearing loss, and for retinal degeneration did not identify any mutations. Biallelic TUBGCP6 mutations cause microcephalic primordial dwarfism and additional congenital anomalies, including retinopathy6. Given the recessive inheritance and additional symptoms associated with mutations in TUBGCP6 (which are not present in the affected family members analyzed in our study), the apparently monoallelic variant most likely represents carriership for an unrelated disorder. Our results from NGS panel analysis thus largely excluded not only mutations in the coding sequences of the Usher syndrome genes and genes causing similar syndromes (e.g. USH3-like PHARC due to ABHD12 mutations7), but also simultaneous mutations in a deafness gene and an RP gene mimicking Usher syndrome. Quantitative analysis of NGS reads did not indicate large copy number variations (CNVs) such as deletions of one or several contiguous exons. Read the entire article References Mathur, P. & Yang, J. Usher syndrome: Hearing loss, retinal degeneration and associated abnormalities. Biochim Biophys Acta 1852, 406–420, doi:10.1016/j.bbadis.2014.11.020 (2015). Ness, S. L. et al. Genetic homogeneity and phenotypic variability among Ashkenazi Jews with Usher syndrome type III. J Med Genet 40, 767–772, doi:10.1136/jmg.40.10.767 (2003). Khan, M. I. et al. CLRN1 mutations cause nonsyndromic retinitis pigmentosa. Ophthalmology 118, 1444–1448, doi:10.1016/j.ophtha.2010.10.047 (2011). Ebermann, I. et al. Deafblindness in French Canadians from Quebec: a predominant founder mutation in the USH1C gene provides the first genetic link with the Acadian population. Genome Biol 8, R47, doi:10.1186/gb-2007-8-4-r47 (2007). Bonnet, C. et al. An innovative strategy for the molecular diagnosis of Usher syndrome identifies causal biallelic mutations in 93% of European patients. Eur J Hum Genet 24, 1730–1738, doi:10.1038/ejhg.2016.99 (2016). Martin, C. A. et al. Mutations in PLK4, encoding a master regulator of centriole biogenesis, cause microcephaly, growth failure and retinopathy. Nat Genet 46, 1283–1292, doi:10.1038/ng.3122 (2014). Eisenberger, T. et al. Targeted next-generation sequencing identifies a homozygous nonsense mutation in ABHD12, the gene underlying PHARC, in a family clinically diagnosed with Usher syndrome type 3. Orphanet J Rare Dis 7, 59, doi:10.1186/1750-1172-7-59 (2012).

A deep intronic CLRN1 (USH3A) founder mutation generates an aberrant exon and underlies severe Usher syndrome on the Arabian Peninsula Abstract Deaf blindness is mostly due to Usher syndrome caused by recessive mutations in the known genes. Mutation-negative patients therefore either have distinct diseases, mutations in yet unknown Usher genes or in extra-exonic parts of the known genes – to date a largely unexplored possibility. In a consanguineous Saudi family segregating Usher syndrome type 1 (USH1), NGS of genes for Usher syndrome, deafness and retinal dystrophy and subsequent whole-exome sequencing each failed to identify a mutation. Genome-wide linkage analysis revealed two small candidate regions on chromosome 3, one containing the USH3A gene CLRN1, which has never been associated with Usher syndrome in Saudi Arabia. Whole-genome sequencing (WGS) identified a homozygous deep intronic mutation, c.254–649T > G, predicted to generate a novel donor splice site. CLRN1 minigene-based analysis confirmed the splicing of an aberrant exon due to usage of this novel motif, resulting in a frameshift and a premature termination codon. We identified this mutation in an additional two of seven unrelated mutation-negative Saudi USH1 patients. Locus-specific markers indicated that c.254–649T > GCLRN1represents a founder allele that may significantly contribute to deaf blindness in this population. Our finding underlines the potential of WGS to uncover atypically localized, hidden mutations in patients who lack exonic mutations in the known disease genes. Read more.

Royal National Institute of Blind People (RNIB) "Retinitis pigmentosa (RP) is the name given to a group of inherited eye conditions called retinal dystrophies." "A retinal dystrophy such as RP affects the retina at the back of your eye and, over time, stops it from working. This means that RP causes gradual but permanent changes that reduce your vision. How much of your vision is lost, how quickly this happens and your age when it begins depends on the type of RP that you have. The changes in your vision happen over years rather than months, and some people lose more sight than others." Living with RP - Dave's Story - RNIB Series To read more, click here.

Ga vin Arno, Keren J. Carss, Sarah Hull, Ceniz Zihni, Anthony G. Robson, Alessia Fiorentino, UK Inherited Retinal Disease Consortium, Alison J. Hardcastle, Graham E. Holder, Michael E. Cheetham, VIncent Plagnol, NIHR Bioresource - Rare Disease Consortium, Anthony T. Moore, F. Lucy Raymond, Karl Matter, Maria S. Balda, Andrew R. Webster,  Published 2017 Jan 26 | doi:  10.1016/j.ajhg.2016.12.014 Mutations in more than 250 genes are implicated in inherited retinal dystrophy; the encoded proteins are involved in a broad spectrum of pathways. The presence of unsolved families after highly parallel sequencing strategies suggests that further genes remain to be identified. Whole-exome and -genome sequencing studies employed here in large cohorts READ entire article, click here Key Word: ARHGEF18

Lauren A Dalvin , Jackson Abou Chehade , John (pei wen) Chiang , Josefine Fuchs , Raymond Lezzi , Alan D Marmorstein | Investigative Ophthalmology & Visual Science | September 2016 | Vol.57 | pg. 655 | https://iovs.arvojournals.org/article.aspx?articleid=2559455 Purpose Mutations in BEST1 are associated with 5 clinically distinct diseases, commonly referred to as the bestrophinopathies. The bestrophinopathies include adult onset vitelliform dystrophy (AVMD), Best vitelliform macular dystrophy (BVMD), autosomal recessive bestrophinopathy (ARB), autosomal dominant vitreoretinochoroidopathy (ADVIRC), and retinitis pigmentosa (RP). Only one study has identified mutations in BEST1 associated with retinitis pigmentosa (RP), and the findings described in that study were atypical of RP with some features of ADVIRC or ARB. Here we report a new subject with RP apparently due to a novel deletion mutation in BEST1. Methods A 16-year-old male was referred from Denmark with poor visual acuity, visual field loss, and cystoid macular edema. Clinical examination, visual field testing, optical coherence tomography (OCT), OCT angiography (OCTA), electroretinography, and electrooculography were used to confirm the classic RP phenotype. Genetic testing of the proband and both parents was carried out by the University of Oregon, Casey Eye Institute, Molecular Diagnostic Laboratory using a panel of 131 retinal dystrophy genes. Results The proband, but not his parents were found to exhibit a classical RP phenotype, which included extensive bone spicules and cystoid macular edema in the presence of generalized visual field constriction, depressed rod and cone electroretinogram (ERG) responses, and reduced Arden ratios on electrooculogram (EOG). A novel heterozygous deletion of 9348 bases (61729891-61733239) from the BEST1 gene resulting in the mutation H422fsX431 was identified in the proband but not in either parent. The deletion begins within exon 10 of the BEST1 gene and extends beyond exon 11 resulting in a frame shift causing deletion of 146aa from Best1, and extending into the adjacent ferritin heavy chain (FTH) gene on the opposite strand of DNA. The proband did not exhibit any symptoms of ferritin deficiency. Conclusions BEST1 mutations play a role in some cases of RP. However, it is difficult to understand why some mutations associate with peripheral retinal degeneration phenotypes like RP and ADVIRC, while others manifest as macular degeneration phenotypes. The identification of additional cases of RP associated with a deletion in BEST1 should improve our ability to elucidate the differential pathogenesis of the 5 bestrophinopathies. This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016 . Click here to read more.

By Raquel Perez-Carro, Marta Corton, Iker Sánchez-Navarro, Olga Zurita, Noelia Sanchez-Bolivar, Rocío Sánchez-Alcudia, Stefan H. Lelieveld, Elena Aller, Miguel Angel Lopez-Martinez, Mª Isabel López-Molina, Patricia Fernandez-San Jose, Fiona Blanco-Kelly, Rosa Riveiro-Alvarez, Christian Gilissen, Jose M Millan, Almudena Avila-Fernandez & Carmen Ayuso | Article number: 19531 | 2016 Abstract Retinitis pigmentosa (RP) is a group of inherited progressive retinal dystrophies (RD) characterized by photoreceptor degeneration. RP is highly heterogeneous both clinically and genetically, which complicates the identification of causative genes and mutations. Targeted next-generation sequencing (NGS) has been demonstrated to be an effective strategy for the detection of mutations in RP. In our study, an in-house gene panel comprising 75 known RP genes was used to analyze a cohort of 47 unrelated Spanish families pre-classified as autosomal recessive or isolated RP. Disease-causing mutations were found in 27 out of 47 cases achieving a mutation detection rate of 57.4%. In total, 33 pathogenic mutations were identified, 20 of which were novel mutations (60.6%). Furthermore, not only single nucleotide variations but also copy-number variations, including three large deletions in the USH2A and EYS genes, were identified. Finally seven out of 27 families, displaying mutations in the ABCA4, RP1, RP2 and USH2A genes, could be genetically or clinically reclassified. These results demonstrate the potential of our panel-based NGS strategy in RP diagnosis. Introduction Retinitis pigmentosa (RP, MIM 268000) is the most common form of inherited retinal degeneration with a prevalence of 1 in 4000 individuals. RP is characterized by primary rod degeneration leading to night blindness, the development of tunnel vision and slow progressive decrease in central vision. However, the disease onset, progression, retinal appearance and final visual outcome may vary significantly among patients, even within the same family. RP is also a highly heterogeneous genetic disorder; the disease can be inherited in different forms including autosomal dominant (adRP) in about 20-40% of the cases, autosomal recessive (arRP) in 30-50% or X-linked trait (xlRP) in 5-15% of the cases. Sporadic cases (sRP) account for about 40% of all diagnoses, although these percentages vary between different populations. Non-Mendelian inheritance patterns such as digenic, mitochondrial or de novo mutations have been also reported, though these account for a minor proportion of cases. Read the article.

DeLuca, AP(DeLuca, Adam P.); Weed, MC(Weed, Matthew C.); Haas, CM(Haas, Christine M.); Halder, JA(Halder, Jennifer A.); Stone, EM(Stone, Edwin M.) | JAMA Ophthalmology | August 2015 | Vol. 133(8) | pgs. 967-968 | doi:10.1001/jamaophthalmol.2015.1463 The clinical features of a known mendelian disease can occasionally be mimicked by the random co-occurrence of 2 different conditions in the same individual. We report a case in which whole-exome sequencing in a patient previously suspected to have Usher syndrome revealed disease-causing mutations in BBS1 and SLC26A4 . This case illustrates how detailed and accurate clinical data are needed to interpret exome-scale genetic testing results. A man in his late 30s was referred for evaluation of suspected Usher syndrome. As a toddler, he was diagnosed as having sensorineural hearing loss due to a Mondini malformation after computed tomography showed characteristic cochlear abnormalities (audiograms shown in Figure 1 ). A few years later, his parents noted that he began tripping over objects and having trouble seeing at night. Several years later, he was diagnosed as having retinitis pigmentosa and suspected to have Usher syndrome. At that time, his best-corrected visual acuity was 20/60 OD and 20/80 OS. By his early 20s, it had decreased to counting fingers OD and 20/800 OS. Aside from a paternal great-great-aunt with deafness, mutism, and normal vision, there were no other affected family members. To buy article, click here

Dunja Lukovic , Ana Artero Castro , Ana Belen Garcia Delgado , María de los Angeles Martín Bernal , Noelia Luna Pelaez , Andrea Díez Lloret , Rocío Perez Espejo , Kunka Kamenarova , Laura Fernández Sánchez , Nicolás Cuenca , Marta Cortón , Avila Fernandez , Anni Sorkio , Heli Skottman , Carmen Ayuso , Slaven Erceg , Shomi S. Bhattacharya  | Scientific Reports | Human iPSC derived disease model of MERTK-associated retinitis pigmentosa | 11 August 2015 | https://doi.org/10.1038/srep12910 Abstract Retinitis pigmentosa (RP) represents a genetically heterogeneous group of retinal dystrophies affecting mainly the rod photoreceptors and in some instances also the retinal pigment epithelium (RPE) cells of the retina. Clinical symptoms and disease progression leading to moderate to severe loss of vision are well established and despite significant progress in the identification of causative genes, the disease pathology remains unclear. Lack of this understanding has so far hindered development of effective therapies. Here we report successful generation of human induced pluripotent stem cells (iPSC) from skin fibroblasts of a patient harboring a novel Ser331Cysfs*5 mutation in the MERTK gene. The patient was diagnosed with an early onset and severe form of autosomal recessive RP (arRP). Upon differentiation of these iPSC towards RPE, patient-specific RPE cells exhibited defective phagocytosis, a characteristic phenotype of MERTK deficiency observed in human patients and animal models. Thus we have created a faithful cellular model of arRP incorporating the human genetic background which will allow us to investigate in detail the disease mechanism, explore screening of a variety of therapeutic compounds/reagents and design either combined cell and gene- based therapies or independent approaches. Introduction Retinitis pigmentosa (RP; OMIM 268000) with a prevalence of 1 in 3,500 individuals is the most common form of hereditary retinal disorder affecting the working age group. RP is characterized by progressive dysfunction and death of mainly the rod photoreceptor cells (PR) of the retina however in some cases retinal pigment epithelium (RPE) cells are also involved, often resulting in permanent blindness. So far 54 genes have been implicated in this disease coding for proteins involved in a myriad of functions such as phototransduction signaling cascade, retinoid cycle, cell-cell adhesion or the cytoskeleton 1 . The disease is inherited in all there Mendelian forms, the autosomal recessive (arRP) being the most common with over 50% of cases. Largely due to the high genetic heterogeneity and unavailability of disease tissue, pathology of the disease remains elusive. Patient-derived induced pluripotent stem cells (iPSCs) provide an unprecedented opportunity to recapitulate disease pathogenicity without the need for genetic manipulation and creation of gene targeted animal models. Human iPSCs, similar to embryonic stem cells (ESC), can be expanded indefinitely in vitro and differentiated into any type of mature cell in the human body, without the ethical and immunogenicity issues associated with ESC 2 . These cells are also valuable for developing therapeutic strategies, drug toxicity screens and development of disease models, in addition to providing a source for cell transplantation therapy. RPE cells and photoreceptors (PR) have been successfully generated from iPSCs (iPSC-RPE and iPSC-PR respectively) by various groups in stepwise differentiation protocols mimicking retinal development by introducing Wnt signaling inhibitors (DKK1), Nodal antagonist Lefty A, Notch pathway inhibitor (DAPT-gamma secretase inhibitor), or IGF-1 3 , 4 , 5 . In contrast, only RPE cells have been generated spontaneously in overgrown iPSC/ESC cultures without the addition of exogenous factors, since derivatives of neuroectoderm appear by default in non-induced cultures 6 , 7 . Generated RPE cells in these studies display a fully mature phenotype and physiological activity in vitro such as phagocytosis, secretion of vascular endothelial growth factor (VEGF) and pigment epithelium-derived factor (PEDF) and epithelial barrier formation. Cellular models of hereditary retinal dystrophies have been successfully created in vitro in Best disease and RP where patients’ fibroblasts were reprogrammed to iPSC and then converted to RPE 8 , 9 or photoreceptor cells 10 , expressing the disease phenotype. iPSC- derived RPE (iPSC-RPE) cells have also been shown to have a protective effect when injected sub-retinaly into the Royal College of Surgeons (RCS) rats 11 and RPE65-defective mice 12 . Moreover, iPSCs have met clinical-grade requirements 13 as a source of RPE grafts and have recently been injected in patients affected by the exudative form (wet-type) of age-related macular degeneration (AMD) 14 . It has been argued that in this form of AMD the dysfunction and loss of RPE cells is the main cause of visual impairment in the elderly. Mer tyrosine kinase receptor (MERTK) belongs to the Tyro3/Axl/Mer (TAM) receptor tyrosine kinase family of proteins distinguished by a conserved intracellular kinase domain and extracellular adhesion molecule-like domain. TAM receptors regulate a variety of processes such as cell proliferation/survival, adhesion, migration, inflammatory response, in a cell- microenvironment- and ligand- specific manner 15 . In previous studies MERTK was found to be disrupted in RCS rats 16 , 17 , a classic model for retinal degeneration inherited as an autosomal recessive trait and found to cause early-onset retinitis pigmentosa in patients 18 . RPE cells fail to phagocytize the shed outer segment (OS) material of PR, a circadian activity performed by RPE cells which serves to renew the damaged lipid and protein components of light exposed PR, while new membranous discs are formed (disc biogenesis) and inserted in the basal part of the OS. As a result, RCS rats exhibit OS associated debris accumulation in the subretinal space, abnormal OS length, eventually leading to the onset of PR degeneration by the P20 stage. Usually complete degeneration occurs by P60. Similar phenotype is observed in merkd mice 19 indicating that the RPE phagocytic defect is the underlying molecular mechanism of disease in humans carrying MERTK mutations. Indeed, the reduced retinal thickness and debris detected in the sub-retinal space in patients harboring the MERTK –splice-site -mutation resembles the observed phenotype in the RCS rat 20 . The distinctive clinical presentation of RP is the only disease manifestation of patients harboring MERTK mutations without any systemic disease or defects of phagocytosis by macrophages, indicating a specialized function of this protein in the RPE cells. In contrast to the detailed clinical understanding of the disease, the mechanism by which MERTK acts during the phagocytosis remains partially unveiled. Outer segments are known to bind to the integrin receptor αvβ5 21 followed by focal adhesion kinase (FAK) activation in the apical membrane of RPE 22 while the MERTK activation occurs via Gas6/Protein S, TUB, TULP1 ligand binding 23 , 24 . The latter is thought to activate autophosphorylation at tyrosine Y-749, Y-753 and Y-754 in the tyrosine kinase domain, which in turn activates the molecular cascade targeting actin or non-muscle myosin II to coordinate the cytoskeletal rearrangements necessary for phagocytic ingestion 25 . Click here to read entire article References Hartong, D. 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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. 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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