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Medical Hypothesis, Discovery Innovation Ophthalmology Journal | Harvey Siy Uy, MD, Pik Sha Chan, MD, and Franz Marie Cruz, MD | 2013 Summer | 2(2) | 52–55. Abstract Unfortunately, at present, degenerative retinal diseases such as retinitis pigmentosa remains untreatable. Patients with these conditions suffer progressive visual decline resulting from continuing loss of photoreceptor cells and outer nuclear layers. However, stem cell therapy is a promising approach to restore visual function in eyes with degenerative retinal diseases such as retinitis pigmentosa. Animal studies have established that pluripotent stem cells when placed in the mouse retinitis pigmentosa models have the potential not only to survive, but also to differentiate, organize into and function as photoreceptor cells. Furthermore, there is early evidence that these transplanted cells provide improved visual function. These groundbreaking studies provide proof of concept that stem cell therapy is a viable method of visual rehabilitation among eyes with retinitis pigmentosa. Further studies are required to optimize these techniques in human application. This review focuses on stem cell therapy as a new approach for vision restitution in retinitis pigmentosa. Hypothesis A potential target disease for stem cell therapy is retinitis pigmentosa (RP). RP is the most commonly inheritable eye disease that causes progressive loss of photoreceptor cells resulting in gradual visual decline. While the onset of RP may occur during infancy, the first symptoms are usually observed in early adulthood, beginning with nyctalopia or night blindness followed by loss of peripheral vision and eventually, as the central photoreceptors in the macula are damaged, loss of fine central vision. Morphologically, these retinas are characterized by centripetal proliferation of bone spicule-like pigmentation, attenuation of retinal blood vessels and optic nerve pallor. At least 50 genetic mutations have been associated with the disease. The Beijing Eye Study reported a prevalence rate of 1 in 1000 and estimates about 1.3 million people are afflicted in China alone. Conclusion Previously, RP was considered a devastating and untreatable condition. These pioneering animal studies provide hopeful evidence for the hypothesis that stem cell therapy is a viable means for visual rehabilitation of RP patients. What is now known is that stem cell therapy can potentially replace degenerate photoreceptors and outer retinal cells. When placed in the appropriate tissue niche, these stem cells not only survive but differentiate into critical retinal cells, develop a retina-like organizational structure and exhibit functional characteristics of full-fledged photoreceptors and outer retinal cells. Further studies are needed to optimize techniques and validate these findings before proceeding to human trials. Click here to read the entire article .

Restoration of RPGR expression in vivo using CRISPR/Cas9 gene editing Abstract Mutations in the gene for Retinitis Pigmentosa GTPase Regulator ( RPGR ) cause the X-linked form of inherited retinal degeneration, and the majority are frameshift mutations in a highly repetitive, purine-rich region of RPGR known as the OFR15 exon. Truncation of the reading frame in this terminal exon ablates the functionally important C-terminal domain. We hypothesized that targeted excision in ORF15 by CRISPR/Cas9 and the ensuing repair by non-homologous end joining could restore RPGR reading frame in a portion of mutant photoreceptors thereby correcting gene function in vivo. We tested this hypothesis in the rd9 mouse, a naturally occurring mutant line that carries a frameshift mutation in RPGR ORF15, through a combination of germline and somatic gene therapy approaches. In germline gene-edited rd9 mice, probing with RPGR domain-specific antibodies demonstrated expression of full length RPGRORF15 protein. Hallmark features of RPGR mutation-associated early disease phenotypes, such as mislocalization of cone opsins, were no longer present. Subretinal injections of the same guide RNA (sgRNA) carried in AAV sgRNA and SpCas9 expression vectors restored reading frame of RPGR ORF15 in a subpopulation of cells with broad distribution throughout the retina, confirming successful correction of the mutation. These data suggest that a simplified form of genome editing mediated by CRISPR, as described here, could be further developed to repair RPGR ORF15 mutations in vivo. Introduction Retinitis pigmentosa (RP) is a heterogenous group of inherited retinal diseases caused by a progressive degeneration of rod and cone photoreceptors that results in the eventual loss of vision. Mutations in more than 200 genes cause RP and collectively these affect one in 3000–5000 people, representing a major cause of inherited forms of blindness globally. Mutations causing X-linked RP (XLRP) are particularly severe with retinal disease presenting within the first few decades of life. The majority of mutations causing XLRP have been identified as loss-of-function alleles in the gene encoding retinitis pigmentosa GTPase regulator ( RPGR ). To read more of this academic paper, click here .

David G. Birch , Janet K. Cheetham , Stephen P. Daiger , Carel Hoyng , Christine Kay , Ian M. MacDonald , Mark E. Pennesi , Lori S. Sullivan | Translational Vision Science and Technology | 2023 June 9 | doi:  10.1167/tvst.12.6.5 Abstract X-linked retinitis pigmentosa (XLRP) is a rare inherited retinal disease manifesting as impaired night vision and peripheral vision loss that progresses to legal blindness. Although several trials of ocular gene therapy for XLRP have been conducted or are in progress, there is currently no approved treatment. In July 2022, the Foundation Fighting Blindness convened an expert panel to examine relevant research and make recommendations for overcoming the challenges and capitalizing on the opportunities in conducting clinical trials of RPGR -targeted therapy for XLRP. Data presented concerned RPGR structure and mutation types known to cause XLRP, RPGR mutation–associated retinal phenotype diversity, patterns in genotype/phenotype relationships, disease onset and progression from natural history studies, and the various functional and structural tests used to monitor disease progression. Panel recommendations include considerations, such as genetic screening and other factors that can impact clinical trial inclusion criteria, the influence of age on defining and stratifying participant cohorts, the importance of conducting natural history studies early in clinical development programs, and the merits and drawbacks of available tests for measuring treatment outcomes. We recognize the need to work with regulators to adopt clinically meaningful end points that would best determine the efficacy of a trial. Given the promise of RPGR -targeted gene therapy for XLRP and the difficulties encountered in phase III clinical trials to date, we hope these recommendations will help speed progress to finding a cure. Introduction X-linked retinitis pigmentosa (XLRP) is a severe, aggressive, inherited retinal disease characterized by progressive photoreceptor deterioration and loss eventually leading to blindness. Pathogenic variants associated with XLRP affect predominately male individuals. Female carriers of a disease-causing variant sometimes can be affected clinically, and, in these cases, typically present with a milder phenotype than male patients, potentially due in part to random or skewed X chromosome inactivation. The most common causes of XLRP are pathogenic variants in two genes, retinitis pigmentosa guanosine triphosphatase regulator ( RPGR ) and RP2 , accounting for approximately 70% and 20% of cases, respectively. Currently, there is no treatment for XLRP. Although several investigational XLRP therapies targeting the RPGR gene have met with early successes in phase I/II clinical studies, the only phase II/III study to read out to date, the XIRIUS study of adeno-associated virus serotype 8 (AAV8) vector-based gene therapy, cotoretigene toliparvovec, failed to meet its primary end point. On July 23, 2022, The Foundation Fighting Blindness convened a virtual meeting of experts in ophthalmology and genetics to discuss the challenges and opportunities in the clinical development of XLRP genetic therapies. Key topics were: Delineating the target patient population, including defining pathogenic RPGR genetic mutations and associated retinal disease clinical phenotypes Establishing XLRP disease course and identifying factors associated with disease outcomes Selecting the structural and functional tests best suited to measure outcomes The Expert Panel's goal was to formulate recommendations for designing XLRP gene therapy clinical studies to provide the best chance of successful treatment development. This article summarizes the meeting's presentations and discussions and the panel's recommendations. Read more, click here.

Victoria Johnson | CGTLive | March 14, 2024 Patients with X-linked retinitis pigmentosa (XLRP) treated with AGTC-501 gene therapy experienced improvements in visual function including retinal sensitivity as assessed by macular Integrity Assessment (MAIA) microperimetry and full-field stimulus threshold (FST) with a favorable benefit-risk profile. Updated, 12-month data from the phase 2 SKYLINE trial (NCT04850118) were presented by Mark Pennesi MD, PhD, Director, Ophthalmic Genetics Retina Foundation Dallas, and Texas Professor of Ophthalmology Professor of Molecular and Medical Genetics, Paul H. Casey Ophthalmic Genetics Division Casey Eye Institute, Oregon Health & Science University, at the 47th Annual Maula Society Meeting, held Feb 07 - 10, 2024, in Palm Springs, California. “The benefit-risk profile is favorable and supports continued clinical development for the treatment of patients with XLRP caused by RPGR mutations,” Pennesi said during his presentation. AGTC-501 delivers a full-length RPGR via an adeno-associated virus (AAV) vector delivered by subretinal injection. The data are from 14 participants, 6 that received low-dose (7.5 E+10 vg/eye) and 8 that received high-dose (6.8 E+11 vg/eye) AGTC-501. Read more, click here ___________________________________________ REFERENCES Pennesi M. Subretinal AGTC-501 Gene Therapy for XLRP: 12-Month Interim Safety & Efficacy Results of the Phase 2 SKYLINE Trial. Presented at: https://www.beacontx.com/news-and-events/subretinal-agtc-501-gene-therapy-for-xlrp-12-month-interim-safety-efficacy-results-of-the-phase-2-skyline-trial/ Beacon Therapeutics Announces Positive 12-Month Data from Phase 2 SKYLINE Trial of AGTC-501 in Patients with X-Linked Retinitis Pigmentosa. News release. Beacon Therapeutics. https://www.prnewswire.com/news-releases/beacon-therapeutics-announces-positive-12-month-data-from-phase-2-skyline-trial-of-agtc-501-in-patients-with-x-linked-retinitis-pigmentosa-302056840.html

Zilin Zhong , Min Yan , Wan Sun , Zehua Wu , Liyun Han , Zheng Zhou , Fang Zheng , Jianjun Chen  | Scientific Reports | 6 | 37840 | 25 November 2016 | https://doi.org/10.1038/srep37840 Abstract Retinitis pigmentosa (RP) is a heterogeneous set of hereditary eye diseases, characterized by selective death of photoreceptor cells in the retina, resulting in progressive visual impairment. Approximately 20–40% of RP cases are autosomal dominant RP (adRP). In this study, a Chinese ADRP family previously localized to the region between D1S2819 and D1S2635 was sequenced via whole-exome sequencing and a variant c.1345C > G (p.R449G) was identified in PRPF3 . The Sanger sequencing was performed in probands of additional 95 Chinese ADRP families to investigate the contribution of PRPF3 to adRP in Chinese population and another variant c.1532A > C (p.H511P) was detected in one family. These two variants, co-segregate with RP in two families respectively and both variants are predicted to be pathological. This is the first report about the spectrum of PRPF3 mutations in Chinese population, leading to the identification of two novel PRPF3 mutations. Only three clustered mutations in PRPF3 have been identified so far in several populations and all are in exon 11. Our study expands the spectrum of PRPF3 mutations in RP. We also demonstrate that PRPF3 mutations are responsible for 2.08% of adRP families in this cohort indicating that PRPF3 mutations might be relatively rare in Chinese ADRP patients. Introduction Retinitis pigmentosa (RP) refers to a heterogeneous set of hereditary retinal degenerative disorders which are responsible for the blindness of more than 1.5 million people worldwide and affect about 1 in 1000 people in China. RP is characterized by a selective death of photoreceptors that are light-sensing cells in the retina, resulting in progressive visual impairment 1 , 2 , 3 .There are three modes of Mendelian inheritance in RP—autosomal-dominant RP (adRP), autosomal-recessive RP (arRP), and X-linked RP (XLRP) 1 . Approximately 20–40% of RP cases are ADRP and mutations in over 20 genes are known to cause ADRP. Amongst ADRP causative genes are an unusual class— pre-mRNA splicing genes 4 — eight of which are ubiquitous core snRNP proteins ( PRPF3 , PRPF8, PRPF3 1, PRPF4, SNRNP200, and PRPF6) and splicing factors (RP9 and DHX38). Mutations in those genes ubiquitously expressed and essential for splicing, have so far been reported to cause a disease that displays retina-specific phenotype 5 . PRPF3 (RP18, OMIM 601414) gene spans approximately 32 kb at chromosome 1q21 6 , contains 16 exons and encodes a protein of 683 amino acids in length with a calculated molecular weight of 77 kDa 7 , which is a human homologue of the yeast U4/U6-associated splicing factor Prp3. Only three clustered PRPF3 mutations, c.1482C > T (p.T494M), c.1478C > T (p.P493S) and c.1466C > A (p.A489D), have been identified thus far in RP in several populations. The mutation T494M is the most frequently detected substitution in PRPF3 while P493S occurs rather sporadically 5 . All the mutations are in the exon11 (c.1427–1526) of PRPF3 and previous surveys failed to identify mutations outside of this exon. Therefore, only the region c.1427–1526 was screened for testing PRPF3 mutations in some reported studies 8 , 9 . In this work, we identified two novel PRPF3 mutations, c.1345C > G (p.R449G) and c.1532A > C (p.H511P), in two Chinese families with adRP. Furthermore, our study demonstrates that PRPF3 mutations are responsible for 2.08% of adRP families in our cohort indicating that PRPF3 mutation might be relatively rare in Chinese patients with adRP. Clinical Evaluations of adRP Families The pedigree of Family 020001 indicates a dominant inheritance pattern of three generations ( Fig. 1 ). Medical history of all the affected individuals shows that early onset of night blindness is at age 4 to 10 years old, with subsequent loss of far peripheral vision after 20 years. Clinical details of that family were previously described 10 . Additional 95 Chinese families had a primary diagnosis of RP based on clinical descriptions provided by the referring clinicians at the time of enrollment. The inheritance pattern of those RP families is AD ( Fig. 1 ). Read more, click here REFERENCE Hartong, D. T., Berson, E. L. & Dryja, T. P. Retinitis pigmentosa. The Lancet 368, 1795–1809 (2006). Xu, L., Hu, L., Ma, K., Li, J. & Jonas, J. B. Prevalence of retinitis pigmentosa in urban and rural adult Chinese: The Beijing Eye Study. Eur J Ophthalmol 16, 865–6 (2006). Bird, A. C. Retinal photoreceptor dystrophies LI. Edward Jackson Memorial Lecture. Am J Ophthalmol. 119, 543–62 (1995). Liu, M. M. & Zack, D. J. Alternative splicing and retinal degeneration. Clin Genet 84, 142–9 (2013). Ruzickova, S. & Stanek, D. Mutations in spliceosomal proteins and retina degeneration. RNA Biol 1–9 (2016). Heng, H. H., Wang, A. & Hu, J. Mapping of the human HPRP3 and HPRP4 genes encoding U4/U6-associated splicing factors to chromosomes 1q21.1 and 9q31-q33. Genomics 48, 273–5 (1998). Chakarova, C. F. et al. Mutations in a third member of pre-mRNA splicing factor genes, implicated in autosomal dominant retinitis pigmentosa. Hum Mol Genet 11, 87–92 (2002). Sullivan, L. S. et al. Prevalence of Mutations in eyeGENE Probands With a Diagnosis of Autosomal Dominant Retinitis Pigmentosa. Invest Ophthalmol Vis Sci 54, 6255–61 (2013). Sullivan, L. S. et al. Prevalence of disease-causing mutations in families with autosomal dominant retinitis pigmentosa: a screen of known genes in 200 families. Invest Ophthalmol Vis Sci 47, 3052–64 (2006). Yuan, Y., Zhou, X., Wang, F., Yan, M. & Ding, F. Evidence for a novel autosomal dominant retinitis pigmentosa linked to chromosome 1p22.1-q12 in a Chinese family. Curr Eye Res 36, 154–67 (2011). Wan, R. et al. The 3.8 A structure of the U4/U6.U5 tri-snRNP: Insights into spliceosome assembly and catalysis. Science 351, 466–75 (2016). Vaclavik, V., Gaillard, M. C., Tiab, L., Schorderet, D. F. & Munier, F. L. Variable phenotypic expressivity in a Swiss family with autosomal dominant retinitis pigmentosa due to a T494M mutation in the PRPF3 gene. Molecular Vision 16, 467–475 (2010). Marti’nez-Gimeno, M. et al. Mutations in the Pre-mRNA Splicing-Factor Genes PRPF3 ,PRPF8, and PRPF3 1in Spanish Families with Autosomal Dominant Retinitis Pigmentosa. Investigative Opthalmology & Visual Science 44, 2171 (2003). Kim, C. et al. Microarray-based mutation detection and phenotypic characterization in Korean patients with retinitis pigmentosa. Mol Vis 18, 2398–410 (2012). Audo, I. et al. Development and application of a next-generation-sequencing (NGS) approach to detect known and novel gene defects underlying retinal diseases. Orphanet J Rare Dis. 7, 8 (2012). Wada, Y., Itabashi, T., Sato, H. & Tamai, M. Clinical features of a Japanese family with autosomal dominant retinitis pigmentosa associated with a Thr494Met mutation in the HPRP3 gene. Graefes Arch Clin Exp Ophthalmol 242, 956–61 (2004). Gamundi, M. J. et al. Transcriptional expression of cis-acting and trans-acting splicing mutations cause autosomal dominant retinitis pigmentosa. Hum Mutat 29, 869–78 (2008). Agafonov, D. E. et al. Molecular architecture of the human U4/U6.U5 tri-snRNP. Science 351, 1416–20 (2016). Blencowe, B. J. & Ouzounis, C. A. The PWI motif: a new protein domain in splicing factors. Trends Biochem Sci 24, 179–80 (1999). Marchler-Bauer, A. et al. The Conserved Domain Database (CDD). Nucleic Acids Res. 43 (Database issue): D222–D226 (2015).

Byron L. Lam, MD; Hendrik P. N. Scholl, MD; Daneal Doub, B.Sc , PharmaD; Marvin Sperling, MD; Mahmoud Hashim, PhD; Nan Li, PhD | The Journal of Retinal and Vitreous Diseases | January 2024 | DOI: 10.1097/IAE.0000000000003920 Purpose Retinitis pigmentosa GTPase regulator–associated X-linked retinitis pigmentosa ( RPGR -associated XLRP) is a rare and severe form of retinitis pigmentosa, resulting in progressive visual impairment; however, disease progression data are limited. A systematic literature review was conducted to assess available data on disease progression in RPGR -associated XLRP. Methods PubMed, Embase, and select congress abstracts were evaluated through June 2022. Eligible studies included results specific to RPGR -associated XLRP or populations with ≥80% of patients with retinitis pigmentosa carrying disease-causing RPGR variants. End points of interest included visual acuity, visual field, ellipsoid zone width, progression to blindness, and patient-reported outcomes. Results Fourteen studies met ≥1 end point of interest. Progressive declines in visual acuity, visual field, and ellipsoid zone width were reported across studies. Nearly all publications reported annual declines in visual acuity (3.5%–8.2%). Annual visual field declines ranged from 4.2% to 13.3%. Changes in retinal structure were also observed (ellipsoid zone width changes: −177 to −830 µ m/year). Most studies measured blindness using visual acuity; visual field–based definitions resulted in blindness by age ∼25 years. Patient-reported outcome data were limited. Conclusion Published evidence shows that patients with RPGR -associated XLRP experience progressive decline in visual acuity, visual field, and ellipsoid zone width, eventually resulting in blindness. Additional longitudinal data with standardized end points and expanded collection of patient-reported outcomes are needed to assess visual decline in RPGR -associated XLRP. Read more, click here

Jasmina Cehajic-Kapetanovic,  Michelle E. McClements, Jennifer Whitfield, Morag Shanks, Penny Clouston, Robert E. MacLaren | JAMA Ophthalmoly |  2020 September 4 | Vol 138, Issue 11 | 1151-58  | doi:10.1001/jamaophthalmol.2020.3634 Key Question " Can a mild RPGR phenotype be explained by impaired splicing caused by a novel pathogenic variant?" Results  "An 84-year-old man was referred with clinical diagnosis of choroideremia and possible inclusion into a gene therapy trial. He presented with late-stage retinal degeneration and unusually preserved visual acuity (78 and 68 ETRDS letters) that clinically resembled choroideremia. His 23-year-old grandson was still in early stages of degeneration but showed a very different clinical picture, typical of retinitis pigmentosa. Next-generation sequencing identified a sole RPGR c.779-5T>G variant of undetermined pathogenicity in both cases. The daughter of the proband showed an RPGR carrier phenotype and was confirmed to carry the same variant. The molecular analysis confirmed that the RPGR c.779-5T>G variation reduced the efficiency of intron splicing compared with wild type, leading to a population of mutant and normal transcripts. The predicted consequences of the pathogenic variant are potential use of an alternative splice acceptor site or complete skipping of exon 8, resulting in truncated forms of the RPGR protein with different levels of glutamylation." Conclusions and Relevance  "These results support the importance of careful interpretation of inconsistent clinical phenotypes between family members. Using a molecular splicing assay, a new pathogenic variant in a noncoding region of RPGR was associated with a proportion of normal and hypomorphic RPGR, where cones are likely to survive longer than expected, potentially accounting for the preserved visual acuity observed in this family." Read article, click here

Last updated January 24, 2021 SUMMARY Inherited retinal degenerations (IRDs), including retinitis pigmentosa (RP) refer to a heterogeneous group of Mendelian disorders caused by mutations in over 200 genes and resulting in vision loss due to loss of structure and function of rod and/or cone photoreceptors. Among the most common genetic causes of IRDs are mutations in the RPGR gene located on the X-chromosome; by far the majority of the RPGR mutations are located in the ORF15 exon of the gene. Most, but not all, patients with RPGR-ORF15 mutations are diagnosed with X-linked RP (XLRP). In addition to causing visual disability in humans, naturally-occurring mutations in ORF15 exon are also found in dogs and mice with retinal degeneration. The exact function of RPGR in the rod and cone photoreceptors remains poorly understood but it is suggested to be involved in regulating ciliary transport. Successful experiments in gene augmentation therapy at different disease stages of dogs with RPGR-ORF15 mutations have set a clear path for clinical trials of gene augmentation therapy in patients. Cideciyan Lab has been involved with better understanding and potentially treating XLRP for over 25 years. Our work includes details of disease expression in hemizygous male patients and heterozygous female carriers, as well as understanding of retinal disease features in mice and dogs. More recently, the lab has been concentrating on gene augmentation therapy applied to dogs with RPGR-ORF15 mutations, specific disease features in patients in order to determine when and where to treat, and what outcomes to use, and hypotheses based on RPGR isoform imbalance in different ORF15 mutations. Click here to read original article and the 20 publications on XLRP RPGR. Contact Cideciyan Lab Scheie Eye Institute 51 North 39th Street Philadelphia, PA 19104 215-662-9986

Yuyu Li,  Ruyi Li ,  Hehua Dai, and  Genlin Li  |  BMC Ophthalmoly | 15 2022 Jan | 22, 27 |  doi.org/10.1186/s12886-021-02242-5 Abstract Background Retinitis pigmentosa (RP) is a genetically heterogeneous disease with 89 causative genes identified to date. However, only approximately 60% of RP cases genetically solved to date, predicating that many novel disease-causing variants are yet to be identified. The purpose of this study is to identify novel variants in PDE6A and PDE6B genes and present its phenotypes in patients with retinitis pigmentosa in Chinese families. Methods Five retinitis pigmentosa patients with PDE6A variants and three with PDE6B variants were identified through a hereditary eye disease enrichment panel (HEDEP), all patients’ medical and ophthalmic histories were collected, and ophthalmological examinations were performed, followed by an analysis of the possible causative variants. Sanger sequencing was used to verify the variants. Results We identified 20 variants in eight patients: 16 of them were identified in either PDE6A or PDE6B in a compound heterozygous state. Additional four heterozygous variants were identified in the genes ADGRA3, CA4, OPTN, RHO. Two novel genetic changes in PDE6A were identified (c.1246G > A and c.1747 T > A), three novel genetic changes in PDE6B were identified (c.401 T > C, c.2293G > C and c.1610-1612del), out of the novel identified variants one was most probably non-pathogenic (c.2293G > C), all other novel variants are pathogenic. Additional variant was identified in CA4 and RHO, which can cause ADRP (c.243G > A, c.688G > A). In addition, a novel variant in ADGRA3 was identified (c.921-1G > A). Conclusions This study reveals novel and known variants in PDE6A and PDE6B genes in Chinese families with autosomal recessive RP, and expands the clinical and genetic findings of photoreceptor-specific enzyme deficiencies. Background Retinitis pigmentosa (RP, OMIM 268000) is a heterogeneous group of inherited retinal dystrophy (IRD) characterized by night blindness, retinal degeneration with bone spicule pigmentation, constricted visual fields, and progressive disease course. The prevalence of RP is approximately 1 per 4000 persons [ 1 ]. Retinitis pigmentosa (RP) is a genetically heterogeneous disease with 89 causative genes identified to date. However, only approximately 60% of RP cases genetically solved to date, predicating that many novel disease-causing variants are yet to be identified ( https://sph.uth.edu/retnet/sum-dis.htm 2021.04.28). The gene therapy and stem cell therapy for retinitis pigmentosa has a promising future, so the identification of novel causative variants is becoming increasingly important. Phosphodiesterase 6(PDE6) enzyme is a heterotetrameric protein consisting of alpha (PDE6A;180,071), beta (PDE6B; 180072), and 2 gamma subunits (PDE6G; 180,073) [ 2 ]. Both alpha and beta subunits are required for full phosphodiesterase activity, and mutations in genes encoding those subunits are known to cause autosomal recessive RP. The mechanisms by which PDE6A and PDE6B mutations lead to RP are probably similar because PDE6A and PDE6B subunits are enzymatically equivalent [ 3 ] and may lead to rod followed by cone death [ 4 ]. Mutations in PDE6A are found in a very low percentage of patients with RP as showed first in a study by Huang and coworkers, suggesting a frequency of < 1% [ 3 ]. Screening of about 160 patients with recessive RP in North America in a subsequent study found a frequency of mutations of approximately 3–4% [ 4 ]. Mutations in PDE6B are found in a frequency of about 4% in patients from North America [ 1 , 5 , 6 , 7 ]. There is no statistics date about incidence rate in Chinese family. Because of the low incidence, many novel disease-causing variants are yet to be identified. The purpose of this study is to report the causative variants of Chinese RP families with PDE6A and PDE6B variants, expanding the clinical and genetic findings of photoreceptor-specific enzyme deficiencies. Click here to read entire article References Hartong DT, Berson EL, Dryja TP. Retinitis pigmentosa. Lancet. 2006;368:1795–809. Khramtsov NV, Feshchenko EA, Suslova VA, Shmukler BE, Terpugov BE, Rakitina TV, et al. The human rod photoreceptor cGMP phosphodiesterase β-subunit: Structural studies of its cDNA and gene. FEBS Lett. 1993;327:275–8.   Huang SH, Pittler SJ, Huang X, Oliveira L, Berson EL, Dryja TP. Autosomal recessive retinitis pigmentosa caused by mutations in the alpha subunit of rod cGMP phosphodiesterase. Nat Genet. 1995;11:468–71. Dryja TP, Rucinski DE, Chen SH, Berson EL. Frequency of mutations in the gene encoding the alpha subunit of rod cGMP-phosphodiesterase in autosomal recessive retinitis pigmentosa. Invest Ophthalmol Vis Sci. 1999;40:1859–65. Daiger SP, Bowne SJ, Sullivan LS. Perspective on genes and mutations causing retinitis pigmentosa. Arch Ophthalmol. 2007;125:151–8. Tsang SH, Tsui I, Chou CL, Zernant J, Haamer E, Iranmanesh R, et al. A novel mutation and phenotypes in phosphodiesterase 6 deficiency. Am J Ophthalmol. 2008;146:780–8. McLaughlin ME, Ehrhart TL, Berson EL, Dryja TP. Mutation spectrum of the gene encoding the beta subunit of rod phosphodiesterase among patients with autosomal recessive retinitis pigmentosa. Proc Natl Acad Sci U S A. 1995;92:3249–53.

Alejandro Estrada-Cuzcano , Kornelia Neveling , Susanne Kohl , Eyal Banin , Ygal Rotenstreich , Dror Sharon , Tzipora C Falik-Zaccai , Stephanie Hipp , Ronald Roepman , Bernd Wissinger , Stef JF Letteboer , Dorus A Mans , Ellen AW Blokland , Michael P Kwint , Sabine J Gijsen , Ramon AC van Huet , Rob WJ Collin , H Scheffer , Joris A Veltman , Eberhart Zrenner , Anneke I den Hollander , B Jeroen Klevering , Frans PM Cremers | American Journal Human Genetics | 2012 Jan 13 | Vol. 90, Issue 1 | pgs. 102–109 | doi: 10.1016/j.ajhg.2011.11.015 Abstract Cone-rod dystrophy (CRD) and retinitis pigmentosa (RP) are clinically and genetically overlapping heterogeneous retinal dystrophies. By using homozygosity mapping in an individual with autosomal-recessive (ar) RP from a consanguineous family, we identified three sizeable homozygous regions, together encompassing 46 Mb. Next-generation sequencing of all exons, flanking intron sequences, microRNAs, and other highly conserved genomic elements in these three regions revealed a homozygous nonsense mutation (c.497T>A [p.Leu166∗]) in C8orf37 , located on chromosome 8q22.1. This mutation was not present in 150 ethnically matched control individuals, single-nucleotide polymorphism databases, or the 1000 Genomes database. Immunohistochemical studies revealed C8orf37 localization at the base of the primary cilium of human retinal pigment epithelium cells and at the base of connecting cilia of mouse photoreceptors. C8orf37 sequence analysis of individuals who had retinal dystrophy and carried conspicuously large homozygous regions encompassing C8orf37 revealed a homozygous splice-site mutation (c.156−2A>G) in two siblings of a consanguineous family and homozygous missense mutations (c.529C>T [p.Arg177Trp]; c.545A>G [p.Gln182Arg]) in siblings of two other consanguineous families. The missense mutations affect highly conserved amino acids, and in silico analyses predicted that both variants are probably pathogenic. Clinical assessment revealed CRD in four individuals and RP with early macular involvement in two individuals. The two CRD siblings with the c.156−2A>G mutation also showed unilateral postaxial polydactyly. These results underline the importance of disrupted ciliary processes in the pathogenesis of retinal dystrophies. Main Text Retinitis pigmentosa (RP [MIM 268000 ]) is the most common inherited retinal degeneration and has an estimated worldwide prevalence of 1/4,000 individuals. 1 RP is initially characterized by rod photoreceptor dysfunction, giving rise to night blindness, which is followed by progressive rod and cone photoreceptor dystrophy, resulting in midperipheral vision loss, tunnel vision, and sometimes blindness. The disease is genetically highly heterogeneous and displays all Mendelian patterns of inheritance. In addition, there are some cases with mitochondrial mutations and digenic inheritance. 2 , 3 Thus far, mutations in 34 genes have been associated with nonsyndromic autosomal-recessive (ar) RP (RetNet). 3 In contrast to RP, cone-rod dystrophy (CRD [MIM 120970 ]) is characterized by a primary loss of cone photoreceptors and subsequent or simultaneous loss of rod photoreceptors. 4 , 5 The disease in most cases becomes apparent during primary-school years. The symptoms include photoaversion, a decrease in visual acuity with or without nystagmus, color-vision defects, and decreased sensitivity of the central visual field. Because rods are also involved, night blindness and peripheral vision loss can occur. The diagnosis of CRD is mainly based on electroretinogram (ERG) recordings, in which cone (photopic) responses are more severely reduced than, or equally as reduced as, rod (scotopic) responses. 5 , 6 CRD occurs in 1/40,000 individuals 4 , 5 and also displays all types of Mendelian inheritance. Mutations in five genes i.e., ABCA4 (MIM 601691 ), ADAM9 (MIM 602713 ), CDHR1 (MIM 609502 ), CERKL (MIM 608381 ), and RPGRIP1 (MIM 605446 ) have thus far been implicated in nonsyndromic arCRD. 7 , 8 , 9 , 10 , 11 Genes harboring arCRD- and arRP-associated mutations encode proteins that are involved in phototransduction, vitamin A (retinoid) metabolism, transport along the connecting cilium, cell-to-cell signaling or synaptic interaction, gene regulation, and phagocytosis. 3 Mutations in these genes are estimated to underlie ∼50% of the cases. We aimed to identify the genetic defects associated with retinal dystrophies and to clinically investigate individuals with RP and CRD. The tenets of the Declaration of Helsinki were followed, and, in accordance with approvals gathered from the appropriate institutional review boards, informed consent was obtained from all participating individuals prior to the donation of blood samples. Homozygosity mapping has proven to be a fruitful method of identifying mutations underlying autosomal-recessive retinal diseases 12 , 13 , 14 , 15 , 16 and of establishing genotype-phenotype correlations. 17 , 18 To identify the genetic defect in a consanguineous family with RP (family 1; Figure 1 A), we analyzed the DNA of individual IV:1 by using an Affymetrix GeneChip Human Mapping 250K SNP array (Affymetrix, Santa Clara, CA, USA) and analyzed the SNP data by using Partek Genomic Suite software (Partek, St. Louis, MO, USA). The analyses showed three large homozygous regions of 7.7 Mb (4q34.3-q35.1, rs2128423–rs59156350), 31.6 Mb (8q22.1-q24.13, rs279475–rs7013593), and 7.0 Mb (11p11.2-q11, rs11039487–rs17494990). Because more than 261 genes were present in these three chromosomal regions, a targeted next-generation sequencing (NGS) approach was used. Sequence capture was done on a 385K sequence-capture array (Roche NimbleGen, Madison, WI, USA). The array design comprised all coding and noncoding exons of these regions, including surrounding sequences that covered the splice sites. The array design harbored additional targeted regions used for similar analyses of homozygous regions in two other families. In total, the design included 4,952 targets, comprising 1,903,789 bp. Sequence capture was done according to the manufacturer's (Roche NimbleGen's) instructions with the Titanium optimized protocol as described by Hoischen et al. 19 The enriched DNA regions of individual IV:1 from family 1 were sequenced on one of four lanes of a Roche 454 sequencing run, yielding 86 Mb of sequence data. Approximately 86% of the sequences were mapped back to unique regions of the human genome (hg18, NCBI build 36.1) with the use of the Roche Newbler software (version 2.3). Of all mapped reads, 91% were located on or near the targeted regions (i.e., within 500 bp). This was sufficient to reach an average of 19.3-fold coverage for all target regions. For the regions of interest, fewer than 2.6% of all targeted sequences were not covered, and only 22% of the target sequence was covered fewer than ten times. The Roche 454 software detected a total of 2,755 high-confidence variants, i.e., it identified the variants in at least three reads. We used a custom-made data-analysis pipeline as described elsewhere 19 to annotate detected variants with various types of information, including known SNPs, amino acid substitutions, genomic location, and evolutionary conservation. A total of 2,573 variants either were found to represent known SNPs or overlapped with a known polymorphic region (dbSNP129); they were therefore not considered to be likely disease-causing variants. Click here to read entire article References Haim M. Epidemiology of retinitis pigmentosa in Denmark. Acta Ophthalmol. Scand. Suppl. 2002;233:1–34. doi: 10.1046/j.1395-3907.2002.00001.x. Daiger S.P., Bowne S.J., Sullivan L.S. Perspective on genes and mutations causing retinitis pigmentosa. Arch. Ophthalmol. 2007;125:151–158. doi: 10.1001/archopht.125.2.151. Berger W., Kloeckener-Gruissem B., Neidhardt J. The molecular basis of human retinal and vitreoretinal diseases. Prog. Retin. Eye Res. 2010;29:335–375. doi: 10.1016/j.preteyeres.2010.03.004. Michaelides M., Hunt D.M., Moore A.T. The cone dysfunction syndromes. Br. J. Ophthalmol. 2004;88:291–297. doi: 10.1136/bjo.2003.027102. Hamel C.P. Cone rod dystrophies. Orphanet J. Rare Dis. 2007;2:7. doi: 10.1186/1750-1172-2-7. Szlyk J.P., Seiple W., Fishman G.A., Alexander K.R., Grover S., Mahler C.L. Perceived and actual performance of daily tasks: relationship to visual function tests in individuals with retinitis pigmentosa. Ophthalmology. 2001;108:65–75. doi: 10.1016/s0161-6420(00)00413-9. Maugeri A., Klevering B.J., Rohrschneider K., Blankenagel A., Brunner H.G., Deutman A.F., Hoyng C.B., Cremers F.P.M. Mutations in the ABCA4 (ABCR) gene are the major cause of autosomal recessive cone-rod dystrophy. Am. J. Hum. Genet. 2000;67:960–966. doi: 10.1086/303079. Ostergaard E., Batbayli M., Duno M., Vilhelmsen K., Rosenberg T. Mutations in PCDH21 cause autosomal recessive cone-rod dystrophy. J. Med. Genet. 2010;47:665–669. doi: 10.1136/jmg.2009.069120. Parry D.A., Toomes C., Bida L., Danciger M., Towns K.V., McKibbin M., Jacobson S.G., Logan C.V., Ali M., Bond J., et al. Loss of the metalloprotease ADAM9 leads to cone-rod dystrophy in humans and retinal degeneration in mice. Am. J. Hum. Genet. 2009;84:683–691. doi: 10.1016/j.ajhg.2009.04.005. Aleman T.S., Soumittra N., Cideciyan A.V., Sumaroka A.M., Ramprasad V.L., Herrera W., Windsor E.A., Schwartz S.B., Russell R.C., Roman A.J., et al. CERKL mutations cause an autosomal recessive cone-rod dystrophy with inner retinopathy. Invest. Ophthalmol. Vis. Sci. 2009;50:5944–5954. doi: 10.1167/iovs.09-3982. Hameed A., Abid A., Aziz A., Ismail M., Mehdi S.Q., Khaliq S. Evidence of RPGRIP1 gene mutations associated with recessive cone-rod dystrophy. J. Med. Genet. 2003;40:616–619. doi: 10.1136/jmg.40.8.616. Collin R.W.J., Littink K.W., Klevering B.J., van den Born L.I., Koenekoop R.K., Zonneveld M.N., Blokland E.A., Strom T.M., Hoyng C.B., den Hollander A.I., Cremers F.P. Identification of a 2 Mb human ortholog of Drosophila eyes shut/spacemaker that is mutated in patients with retinitis pigmentosa. Am. J. Hum. Genet. 2008;83:594–603. doi: 10.1016/j.ajhg.2008.10.014. Collin R.W.J., van den Born L.I., Klevering B.J., de Castro-Miró M., Littink K.W., Arimadyo K., Azam M., Yazar V., Zonneveld M.N., Paun C.C., et al. High-resolution homozygosity mapping is a powerful tool to detect novel mutations causative of autosomal recessive RP in the Dutch population. Invest. Ophthalmol. Vis. Sci. 2011;52:2227–2239. doi: 10.1167/iovs.10-6185. Bandah-Rozenfeld D., Collin R.W.J., Banin E., van den Born L.I., Coene K.L.M., Siemiatkowska A.M., Zelinger L., Khan M.I., Lefeber D.J., Erdinest I., et al. Mutations in IMPG2, encoding interphotoreceptor matrix proteoglycan 2, cause autosomal-recessive retinitis pigmentosa. Am. J. Hum. Genet. 2010;87:199–208. doi: 10.1016/j.ajhg.2010.07.004. den Hollander A.I., Koenekoop R.K., Mohamed M.D., Arts H.H., Boldt K., Towns K.V., Sedmak T., Beer M., Nagel-Wolfrum K., McKibbin M., et al. Mutations in LCA5, encoding the ciliary protein lebercilin, cause Leber congenital amaurosis. Nat. Genet. 2007;39:889–895. doi: 10.1038/ng2066. Littink K.W., Koenekoop R.K., van den Born L.I., Collin R.W.J., Moruz L., Veltman J.A., Roosing S., Zonneveld M.N., Omar A., Darvish M., et al. Homozygosity mapping in patients with cone-rod dystrophy: Novel mutations and clinical characterizations. Invest. Ophthalmol. Vis. Sci. 2010;51:5943–5951. doi: 10.1167/iovs.10-5797. Estrada-Cuzcano A., Koenekoop R.K., Coppieters F., Kohl S., Lopez I., Collin R.W.J., De Baere E.B.W., Roeleveld D., Marek J., Bernd A., et al. IQCB1 mutations in patients with leber congenital amaurosis. Invest. Ophthalmol. Vis. Sci. 2011;52:834–839. doi: 10.1167/iovs.10-5221. Khan M.I., Kersten F.F.J., Azam M., Collin R.W.J., Hussain A., Shah S.T., Keunen J.E.E., Kremer H., Cremers F.P.M., Qamar R., den Hollander A.I. CLRN1 mutations cause nonsyndromic retinitis pigmentosa. Ophthalmology. 2011;118:1444–1448. doi: 10.1016/j.ophtha.2010.10.047. Hoischen A., Gilissen C., Arts P., Wieskamp N., van der Vliet W., Vermeer S., Steehouwer M., de Vries P., Meijer R., Seiqueros J., et al. Massively parallel sequencing of ataxia genes after array-based enrichment. Hum. Mutat. 2010;31:494–499. doi: 10.1002/humu.21221.

An drea Sodi ,  Sandro Banfi ,  Michele Della Corte ,  Francesco Testa, Ilaria Passerini ,  Elisabetta Pelo ,  Settimio Rossi , and  Francesca Simonelli  |  Orphanet Journal of Rare Diseases |  Vol. 16 | Article 257 | 4 Jun 2021 |  doi.org/10.1186/s13023-021-01868-4 Inherited retinal dystrophy caused by confirmed biallelic mutations in the RPE65 gene, which encodes all-trans retinyl ester isomerase, an enzyme critical to the visual cycle, is a serious and sight-threatening autosomal recessive genetic disorder that causes a severe form of rod-cone mediated IRD that eventually progresses to complete blindness. Abstract Background This research aimed to establish recommendations on the clinical and genetic characteristics necessary to confirm patient eligibility for gene supplementation with voretigene neparvovec. Methods An expert steering committee comprising an interdisciplinary panel of Italian experts in the three fields of medical specialisation involved in the management of RPE65 -associated inherited retinal disease (IRD) (medical retina, genetics, vitreoretinal surgery) proposed clinical questions necessary to determine the correct identification of patients with the disease, determine the fundamental clinical and genetics tests to reach the correct diagnosis and to evaluate the urgency to treat patients eligible to receive treatment with voretigene neparvovec. Supported by an extensive review of the literature, a series of statements were developed and refined to prepare precisely constructed questionnaires that were circulated among an external panel of experts comprising ophthalmologists (retina specialists, vitreoretinal surgeons) and geneticists with extensive experience in IRDs in Italy in a two-round Delphi process. Results The categories addressed in the questionnaires included clinical manifestations of RPE65 -related IRD, IRD screening and diagnosis, gene testing and genotyping, ocular gene therapy for IRDs, patient eligibility and prioritisation and surgical issues. Response rates by the survey participants were over 90% for the majority of items in both Delphi rounds. The steering committee developed the key consensus recommendations on each category that came from the two Delphi rounds into a simple and linear diagnostic algorithm designed to illustrate the patient pathway leading from the patient’s referral centre to the retinal specialist centre. Conclusions Consensus guidelines were developed to guide paediatricians and general ophthalmologists to arrive at the correct diagnosis of RPE65 -associated IRD and make informed clinical decisions regarding eligibility for a gene therapy approach to RPE65 -associated IRD. The guidelines aim to ensure the best outcome for the patient, based on expert opinion, the published literature, and practical experience in the field of IRDs. Background Inherited retinal diseases (inherited retinal dystrophies; IRDs) are a heterogeneous group of ocular neurodegenerative disorders resulting from mutations in any one of over 250 causative genes [ 1 ]. They are mostly characterised by progressive retinal degeneration that leads to severe visual impairment and blindness [ 2 , 3 , 4 , 5 , 6 ]. Inherited retinal dystrophy caused by confirmed biallelic mutations in the RPE65 gene, which encodes all-trans retinyl ester isomerase, an enzyme critical to the visual cycle, is a serious and sight-threatening autosomal recessive genetic disorder that causes a severe form of rod-cone mediated IRD that eventually progresses to complete blindness [ 3 , 4 , 5 ]. The spectrum of RPE65 -mediated IRD exhibits common clinical findings, initially characterised by nyctalopia (night blindness), present from early childhood and due to a primary effect on the rod photoreceptors [ 7 , 8 ]. The visual function of individuals affected with IRD declines with age, with deteriorating visual acuity (VA) and progressive loss of retinal structure and function (retinal sensitivity) on visual field testing by Goldmann kinetic perimetry (GVF), often leading to blindness in young adulthood [ 8 , 9 , 10 , 11 ]. The disease course may include earlier or later onset, nystagmus, along with night blindness and loss of vision. Indeed, individuals with biallelic RPE65 mutations may be given one of a variety of clinical diagnoses. Depending on the time of disease onset, severity, rate of progression and presenting phenotype, the most common diagnoses are Leber congenital amaurosis (LCA) and early-onset severe retinal dystrophy (EOSRD) [ 5 , 8 ]. These forms are thought to be responsible for approximately 5% of cases of severe IRDs [ 7 ]. However, a smaller proportion of patients exhibit a milder phenotype with a slower progression, possibly associated with hypomorphic alleles [ 11 , 12 , 13 ]. Initially considered incurable, as the understanding of the pathophysiological mechanisms underlying the subtypes of IRD has expanded, a number of therapeutic approaches to treating IRDs have been proposed, the most advanced of which is gene supplementation therapy [ 6 ]. Monogenic ocular diseases are good candidates for gene transfer therapy, as the eye has favourable anatomical and immunological characteristics, providing a contained physical space protected by the blood-ocular barrier that is particularly suited for local delivery [ 14 ]. Remarkably, RPE65 -associated IRD represents a successful model for the development of ocular gene supplementation therapy applied to monogenic diseases. Click here to read entire article References Daiger SP, Sullivan LS, Browne SJ. RetNet: Summaries of Genes and Loci Causing Retinal Diseases (2020) The University of Texas-Houston Health Science Center. https://sph.uth.edu/retnet/sum-dis.htm . Accessed 29 May 2020 Hamel CP. Gene discovery and prevalence in inherited retinal dystrophies. C R Biol. 2014;337(3):160–6. Hohman TC. Hereditary retinal dystrophy. Handb Exp Pharmacol. 2017;242:337–67. Khan M, Fadaie Z, Cornelis SS, Cremers FPM, Roosing S. Identification and analysis of genes associated with inherited retinal diseases. Methods Mol Biol. 2019;18:343–427.   Kumaran N, Moore AT, Weleber RG, Michaelides M. Leber congenital amaurosis/early-onset severe retinal dystrophy: clinical features, molecular genetics and therapeutic interventions. Br J Ophthalmol. 2017;101(9):1147–54. Vázquez-Domínguez I, Garanto A, Collin RWJ. Molecular therapies for inherited retinal diseases-current standing, opportunities and challenges. Genes (Basel). 2019;10(9):654. den Hollander AI, Roepman R, Koenekoop RK, Cremers FP. Leber congenital amaurosis: genes, proteins and disease mechanisms. Prog Retin Eye Res. 2008;27(4):391–419. Thompson DA, Gyürüs P, Fleischer LL, et al. Genetics and phenotypes of RPE65 mutations in inherited retinal degeneration. Invest Ophthalmol Vis Sci. 2000;41(13):4293–9. Chung DC, Bertelsen M, Lorenz B, et al. The natural history of inherited retinal dystrophy due to biallelic mutations in the RPE65 gene. Am J Ophthalmol. 2019;199:58–70. Kumaran N, Georgiou M, Bainbridge JW, et al. Retinal structure in RPE65-associated retinal dystrophy. Investig Ophthalmol Vis Sci. 2020;61(4):47. Kumaran N, Rubin GS, Kalitzeos A, et al. A cross-sectional and longitudinal study of retinal sensitivity in RPE65-associated Leber congenital amaurosis. Investig Ophthalmol Vis Sci. 2018;59(8):3330–9. Hull S, Holder GE, Robson AG, et al. Preserved visual function in retinal dystrophy due to hypomorphic RPE65 mutations. Br J Ophthalmol. 2016;100(11):1499–505. Lorenz B, Poliakov E, Schambeck M, Friedburg C, Preising MN, Redmond TM. A comprehensive clinical and biochemical functional study of a novel RPE65 hypomorphic mutation. Investig Ophthalmol Vis Sci. 2008;49(12):5235–42.

Sarah Hull,  Nicholas Owen, Farrah Islam, Dhani Tracey-White, Vincent Plagnol, Graham E. Holder, Michel Michaelides, Keren Carss; F. Lucy Raymond, Jean-Michel Rozet, Simon C. Ramsden, Graeme C. M. Black, Isabelle Perrault, Ajoy Sarkar, Mariya Moosajee, Andrew R. Webster, Gavin Arno, Anthony T. Moore |  Investigative Ophthalmology & Visual Science | March 2016 | Vol. 57 | pgs. 1053-1062 | doi.org/10.1167/iovs.15-17976 Abstract Purpose : Mutations in the ciliary transporter gene IFT140, usually associated with a severe syndromic ciliopathy, may also cause isolated retinal dystrophy. A series of patients with nonsyndromic retinitis pigmentosa (RP) due to IFT140 was investigated in this study. Methods : Five probands and available affected family members underwent detailed phenotyping including retinal imaging and electrophysiology. Whole exome sequencing was performed on two probands, a targeted sequencing panel of 176 retinal genes on a further two, and whole genome sequencing on the fifth. Missense mutations of IFT140 were further investigated in vitro using transient plasmid transfection of hTERT-RPE1 cells. Results : Eight affected patients from five families had preserved visual acuity until at least the second decade; all had normal development without skeletal manifestations or renal failure at age 13 to 67 years (mean, 42 years; median, 44.5 years). Bi-allelic mutations in IFT140 were identified in all families including two novel mutations: c.2815T > C (p.Ser939Pro) and c.1422_23insAA (p.Arg475Asnfs*14). Expression studies demonstrated a significantly reduced number of cells showing localization of mutant IFT140 with the basal body for two nonsyndromic mutations and two syndromic mutations compared with the wild type and a polymorphism. Conclusions : This study highlights the phenotype of nonsyndromic RP due to mutations in IFT140 with milder retinal dystrophy than that associated with the syndromic disease. Introduction The outer segments of photoreceptors are highly modified, photosensitive cilia, which lack any capability for protein production. 1 Thus, they are reliant on the intraflagellar transport (IFT) system, which comprises large protein complexes for transport from the cell body to cilium tip and back driven by the motors kinesin-2 and dynein-2, respectively. 2 The IFT-B complex is essential for cilium assembly and anterograde transport, whereas the IFT-A complex is responsible for retrograde transport, with additional roles in anterograde transport by connecting kinesin to the IFT complex and in facilitating entry of proteins in to the cilium. 3 , 4 IFT140, a subunit of IFT-A, is vital for both the development and the maintenance of outer segments and has a specific role in opsin transport across the connecting cilium. 2   Mutations in IFT140 have been associated with Jeune asphyxiating thoracic dystrophy and Mainzer-Saldino syndrome, ciliopathies forming part of a spectrum of skeletal dysplasias now collectively termed short rib thoracic dysplasia 9 with or without polydactyly (SRTD9, mendelian inheritance in man [MIM]#266920). 5 – 7 First described in 1970, patients have variable skeletal features including shortened ribs, short stature, cone-shaped phalangeal epiphyses (prepubertal), brachymesophalangy, and acetabular spurring or metaphyseal defect of the femoral head. 8 Nonskeletal features in the majority of patients include a severe early-onset retinal dystrophy and end-stage renal failure secondary to nephronophthisis by the teenage years, with cerebellar ataxia, epilepsy, facial dysmorphism, learning difficulties, and cholestasis also reported. 5 – 7   Retinitis pigmentosa (RP) is the most common form of inherited retinal dystrophy, with more than 60 genes associated with the nonsyndromic, recessive form. 9 – 12 These include ciliopathy genes such as CEP290 and BBS1, which manifest both syndromic and nonsyndromic phenotypes. 13 , 14 Recently, IFT140 mutations have been identified in patients with isolated retinal dystrophy. 15 , 16 The present study reports eight patients from five families with isolated retinal dystrophy and bi-allelic IFT140 variants with detailed characterization of the ocular phenotype. Functional analysis of two of these variants with protein localization studies in hTERT-RPE1 cells supports their pathogenicity.  Click here to read entire article References Tsujikawa M, Malicki J. Intraflagellar transport genes are essential for differentiation and survival of vertebrate sensory neurons. Neuron . 2004; 42: 703–716. 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. Mukhopadhyay S, Wen X, Chih B, et al. TULP3 bridges the IFT-A complex and membrane phosphoinositides to promote trafficking of G protein-coupled receptors into primary cilia. Genes Dev . 2010; 24: 2180–2193. Wei Q, Zhang Y, Li Y, Zhang Q, Ling K, Hu J. The BBSome controls IFT assembly and turnaround in cilia. Nat Cell Biol . 2012; 14: 950–957. Perrault I, Saunier S, Hanein S, et al. Mainzer-Saldino syndrome is a ciliopathy caused by IFT140 mutations. 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Hum Genet . 2014;133(10):1255–1271. Littink KW, van den Born LI, Koenekoop RK, et al. Mutations in the EYS gene account for approximately 5% of autosomal recessive retinitis pigmentosa and cause a fairly homogeneous phenotype. Ophthalmology . 2010; 117: 2026–2033. den Hollander AI, Koenekoop RK, Yzer S, et al. Mutations in the CEP290 (NPHP6) gene are a frequent cause of Leber congenital amaurosis. Am J Hum Genet . 2006; 79: 556–561. Estrada-Cuzcano A, Koenekoop RK, Senechal A, et al. BBS1 mutations in a wide spectrum of phenotypes ranging from nonsyndromic retinitis pigmentosa to Bardet-Biedl syndrome. Arch Ophthalmol . 2012; 130: 1425–1432. Xu M, Yang L, Wang F, et al. Mutations in human IFT140 cause non-syndromic retinal degeneration. Hum Genet . 2015;134(10):1069–1078. Bifari IN, Elkhamary SM, Bolz HJ, Khan AO. The ophthalmic phenotype of IFT140-related ciliopathy ranges from isolated to syndromic congenital retinal dystrophy [published online ahead of print September 10 2015]. 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