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Zhimeng Zhang, Hehua Dai, Lei Wang, Tianchang Tao, Jing Xu, Xiaowei Sun, Liping Yang, Genlin Li | BMC Ophthalmology | Vol. 19, Article # 240 | 2019 | Background RP (retinitis pigmentosa) is a group of hereditary retinal degenerative diseases. XLRP is a relatively severe subtype of RP. Thus, it is necessary to identify genes and mutations in patients who present with X-linked retinitis pigmentosa. Methods Genomic DNA was extracted from peripheral blood. The coding regions and intron-exon boundaries of the retinitis pigmentosa GTPase regulator (RPGR) and RP2 genes were amplified by PCR and then sequenced directly. Ophthalmic examinations were performed to identify affected individuals from two families and to characterize the phenotype of the disease. Results Mutation screening demonstrated two novel nonsense mutations (c.1541C > G; p.S514X and c.2833G > T; p.E945X) in the RPGR gene. The clinical manifestation of family 1 with mutations in exon 13 was mild. Genotype-phenotype correlation analysis suggested that patients with mutations close to the downstream region of ORF15 in family 2 manifested an early loss of cone function. Family 2 carried a nonsense mutation in ORF15 that appeared to have a semi-dominant pattern of inheritance. All male patients and two female carriers in family 2 manifested pathological myopia (PM), indicating that there may be a distinctive X-linked genotype-phenotype correlation between RP and PM. Conclusions We identified two novel mutations of the RPGR gene, which broadens the spectrum of RPGR mutations and the phenotypic spectrum of the disease in Chinese families. Read the complete article

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

Chunbo Yang, Maria Georgiou, Robert Atkinson, Joseph Collin, Jumana Al-Aama, Sushma Nagaraja-Grellscheid, Colin Johnson, Robin Ali, Lyle Armstrong, Sina Mozaffari-Jovin, and Majlinda Lako | doi.org/10.3389/fcell.2021.700276 Overview Retinitis pigmentosa (RP) is the most common inherited retinal disease characterized by progressive degeneration of photoreceptors and/or retinal pigment epithelium that eventually results in blindness. Mutations in pre-mRNA processing factors ( PRPF3, PRPF4, PRPF6, PRPF8, PRPF31, SNRNP200, and RP9 ) have been linked to 15–20% of autosomal dominant RP (adRP) cases. Current evidence indicates that PRPF mutations cause retinal specific global spliceosome dysregulation, leading to mis-splicing of numerous genes that are involved in a variety of retina-specific functions and/or general biological processes, including phototransduction, retinol metabolism, photoreceptor disk morphogenesis, retinal cell polarity, ciliogenesis, cytoskeleton and tight junction organization, waste disposal, inflammation, and apoptosis. Importantly, additional PRPF functions beyond RNA splicing have been documented recently, suggesting a more complex mechanism underlying PRPF -RPs driven disease pathogenesis. The current review focuses on the key RP- PRPF genes, depicting the current understanding of their roles in RNA splicing, impact of their mutations on retinal cell’s transcriptome and phenome, discussed in the context of model species including yeast, zebrafish, and mice. Importantly, information on PRPF functions beyond RNA splicing are discussed, aiming at a holistic investigation of PRPF -RP pathogenesis. Finally, work performed in human patient-specific lab models and developing gene and cell-based replacement therapies for the treatment of PRPF -RPs are thoroughly discussed to allow the reader to get a deeper understanding of the disease mechanisms, which we believe will facilitate the establishment of novel and better therapeutic strategies for PRPF -RP patients. Introduction Retinitis pigmentosa (RP) is the most common group of inherited retinal disorders characterized by progressive degeneration of photoreceptors and/or the retinal pigment epithelium (RPE). Most RP cases start with night blindness due to the breakdown of rod photoreceptors, which are responsible for night vision. As the disease progresses, mid-peripheral vision is lost (tunnel vision), followed by cone degeneration leading to central vision loss until eventual blindness ( Hartong et al., 2006 ; Berger et al., 2010 ). The prevalence of RP is around 1 in 4000 and there are over 1.5 million people suffering from this condition worldwide ( Verbakel et al., 2018 ). There is no cure for RP although vitamins, nutritional supplementation and small molecules may slow disease progression. To date, more than 70 genetic loci have been involved in the pathogenesis of RP 1 . Approximately half of RP cases have previous family history and fall into three Mendelian modes of inheritance: autosomal recessive (arRP), autosomal dominant (adRP), and X-linked recessive (xlRP) ( Hamel, 2006 ). 50–60% of RP cases are caused by autosomal-recessive inheritance, 30–40% of cases are autosomal dominant, and 5–15% of cases are X-linked. Most of the genes involved in RP ontology are expressed specifically in the retina and/or RPE and contribute to photoreceptor or RPE function. Mutations in the rhodopsin ( RHO ) gene are the most common cause of adRP accounting for 25% of adRP cases. Interestingly, the second most common cause of adRP accounting for 15–20% of adRP cases, is linked to mutations in the ubiquitously expressed pre-mRNA processing factor ( PRPF ) genes, that encode core components of the spliceosome ( Wang et al., 2019 ). Read the entire article References Berger, W., Kloeckener-Gruissem, B., and Neidhardt, J. (2010). The molecular basis of human retinal and vitreoretinal diseases. Prog. Retin. Eye Res. 29, 335–375. Hamel, C. (2006). Retinitis pigmentosa. Orphanet. J. Rare Dis. 1:40. Hartong, D. T., Berson, E. L., and Dryja, T. P. (2006). Retinitis pigmentosa. Lancet 368, 1795–1809. Verbakel, S. K., Van Huet, R. A. C., Boon, C. J. F., Den Hollander, A. I., Collin, R. W. J., Klaver, C. C. W., et al. (2018). Non-syndromic retinitis pigmentosa. Prog. Retin. Eye Res. 66, 157–186. Wang, A. L., Knight, D. K., Vu, T. T., and Mehta, M. C. (2019). Retinitis pigmentosa: review of current treatment. Int. Ophthalmol. Clin. 59, 263–280.

By Arlene Weintraub Mutations in more than 270 genes have been implicated in inherited eye diseases like retinitis pigmentosa. Now, Biogen has formed a research pact with Harvard’s Massachusetts Eye and Ear that’s aimed at developing a gene therapy to help some patients with these blinding diseases. The gene at the center of the new agreement, PRPF31, has been linked to autosomal dominant retinitis pigmentosa. PRPF31 mutations are believed to cause an estimated 25% of all retinitis pigmentosa cases. The partners did not disclose the financial terms of the deal. The tie-up comes eight months after a Mass Eye and Ear team published preclinical research demonstrating a gene therapy technique for repairing cells with mutated PRPF31 genes. The technique partially restored the structure and function of retinal pigment epithelium cells, the team reported in the journal Molecular Therapy Methods & Clinical Development. The research was led by Eric Pierce, M.D., Ph.D., professor at Harvard Medical School and director of the inherited retinal disorders service at Mass Eye and Ear. Read the entire article

Gabrielle Wheway, Liliya Nazlamova , Nervine Meshad, Samantha Hunt, Nicola Jackson, Amanda Churchill | "A combined in silico , in vitro and clinical approach to Characterize Novel Pathogenic Missense Variants in PRPF31 in Retinitis Pigmentosa" Overview At least six different proteins of the spliceosome, including PRPF3, PRPF4, PRPF6, PRPF8, PRPF31, and SNRNP200, are mutated in autosomal dominant retinitis pigmentosa (adRP). These proteins have recently been shown to localize to the base of the connecting cilium of the retinal photoreceptor cells, elucidating this form of RP as a retinal ciliopathy. In the case of loss-of-function variants in these genes, pathogenicity can easily be ascribed. In the case of missense variants, this is more challenging. Furthermore, the exact molecular mechanism of disease in this form of RP remains poorly understood. In this paper we take advantage of the recently published cryo EM-resolved structure of the entire human spliceosome, to predict the effect of a novel missense variant in one component of the spliceosome; PRPF31, found in a patient attending the genetics eye clinic at Bristol Eye Hospital. Monoallelic variants in PRPF31 are a common cause of autosomal dominant retinitis pigmentosa (adRP) with incomplete penetrance. We use in vitro studies to confirm pathogenicity of this novel variant PRPF31 c.341T > A, p.Ile114Asn. This work demonstrates how in silico modeling of structural effects of missense variants on cryo-EM resolved protein complexes can contribute to predicting pathogenicity of novel variants, in combination with in vitro and clinical studies. It is currently a considerable challenge to assign pathogenic status to missense variants in these proteins. Introduction Retinitis pigmentosa (RP) is a progressive retinal degeneration characterized by night blindness and restriction of peripheral vision. Later in the course of the disease, central and color vision can be lost. Many patients experience the first signs of RP between 20 and 40 years but there is much phenotypic variability from age of onset and speed of deterioration to severity of visual impairment ( Hartong et al., 2006 ). Retinitis pigmentosa, whilst classified as a rare disease, is the most common cause of inherited blindness worldwide. It affects between 1:3500 and 1:2000 people ( Golovleva et al., 2010 ; Sharon and Banin, 2015 ), and can be inherited in an autosomal dominant (adRP), autosomal recessive (arRP), or X-linked (xlRP) manner. It may occur in isolation (non-syndromic RP) ( Verbakel et al., 2018 ), or with other features (syndromic RP) as in Bardet–Biedl syndrome, Joubert syndrome and Usher syndrome ( Mockel et al., 2011 ). The condition is extremely heterogeneous, with 64 genes identified as causes of non-syndromic RP, and more than 50 genes associated with syndromic RP (RetNet 1 ). Even with current genetic knowledge, diagnostic detection rate in adRP cohorts remains between 40% ( Mockel et al., 2011 ) and 66% ( Zhang et al., 2016 ), suggesting that many disease genes remain to be identified, and many mutations within known genes require characterization to ascribe pathogenic status. Detection rates are as low as 14% in cohorts of simplex cases (single affected individuals) and multiplex cases (several affected individuals in one family but unclear pattern of inheritance) ( Jin et al., 2008 ). Such cases account for up to 50% of RP cases, so this presents a significant challenge to diagnosis ( Greenberg et al., 1993 ; Haim, 1993 ; Najera et al., 1995 ). The second most common genetic cause of adRP is PRPF31 , accounting for 6% of United States cases ( Sullivan et al., 2013 ) 8% of Spanish cases ( Martin-Merida et al., 2018 ), 8% of French Canadian cases ( Coussa et al., 2015 ), 8% of French cases ( Audo et al., 2010 ), 8.9% of cases in North America ( Daiger et al., 2014 ), 11.1% in small Chinese cohort ( Lim et al., 2009 ), 10% in a larger Chinese cohort ( Xu et al., 2012 ) and 10.5% of Belgian cases ( Van Cauwenbergh et al., 2017 ). However, this is likely to be an underestimate due to variable penetrance of this form of RP, complicating attempts to co-segregate the variant with clinical disease, making genetic diagnosis difficult. Whilst the majority of reported variants in PRPF31 are indels, splice site variants and nonsense variants, large-scale deletions or copy number variations ( Martin-Merida et al., 2018 ), which are easily ascribed pathogenic status, at least eleven missense variants in PRPF31 have been reported in the literature ( Table 1 ). Missense variants are more difficult to characterize functionally than nonsense or splicing mutations ( Cooper and Shendure, 2011 ) and it is likely that there are false negative diagnoses in patients carrying missense mutations due to lack of confidence in prediction of pathogenicity of such variants. This is reflected in the enrichment of PRPF31 missense variants labeled ‘uncertain significance’ in ClinVar, a public repository for clinically relevant genetic variants ( Landrum et al., 2014 , 2016 ). Furthermore, work has shown that some variants annotated as missense PRPF31 variants may in fact be affecting splicing of PRPF31 , introducing premature stop codons leading to nonsense mediated decay (NMD), a common disease mechanism in RP11 ( Rio Frio et al., 2008 ). One example is c.319C > G, which, whilst originally annotated as p.Leu107Val, actually affects splicing rather than an amino acid substitution ( Rio Frio et al., 2008 ). The presence of exonic splice enhancers is often overlooked by genetics researchers. Read entire article References Audo, I., Bujakowska, K., Mohand-Said, S., Lancelot, M. E., Moskova-Doumanova, V., Waseem, N. H., et al. (2010). Prevalence and novelty of PRPF31 mutations in french autosomal dominant rod-cone dystrophy patients and a review of published reports. BMC Med. Genet. 11:145. Cooper, G. M., and Shendure, J. (2011). Needles in stacks of needles: finding disease-causal variants in a wealth of genomic data. Nat. Rev. Genet. 12, 628–640. Coussa, R. G., Chakarova, C., Ajlan, R., Taha, M., Kavalec, C., Gomolin, J., et al. (2015). Genotype and phenotype studies in autosomal dominant retinitis pigmentosa (adrp) of the french canadian founder population. Invest. Ophthalmol. Vis. Sci. 56, 8297–8305. Daiger, S. P., Bowne, S. J., and Sullivan, L. S. (2014). Genes and mutations causing autosomal dominant retinitis pigmentosa. Cold Spring Harb. Perspect. Med. 5:a017129. Golovleva, I., Kohn, L., Burstedt, M., Daiger, S., and Sandgren, O. (2010). Mutation spectra in autosomal dominant and recessive retinitis pigmentosa in northern sweden. Adv. Exp. Med. Biol. 664, 255–262. Greenberg, J., Bartmann, L., Ramesar, R., and Beighton, P. (1993). Retinitis pigmentosa in southern africa. Clin. Genet. 44, 232–235. Haim, M. (1993). Retinitis pigmentosa: problems associated with genetic classification. Clin. Genet. 44, 62–70. Hartong, D. T., Berson, E. L., and Dryja, T. P. (2006). Retinitis pigmentosa. Lancet 368, 1795–1809. Jin, Z. B., Mandai, M., Yokota, T., Higuchi, K., Ohmori, K., Ohtsuki, F., et al. (2008). Identifying pathogenic genetic background of simplex or multiplex retinitis pigmentosa patients: a large scale mutation screening study. J. Med. Genet. 45, 465–472. Landrum, M. J., Lee, J. M., Benson, M., Brown, G., Chao, C., Chitipiralla, S., et al. (2016). ClinVar: public archive of interpretations of clinically relevant variants. Nucleic Acids Res. 44, D862–D868. Landrum, M. J., Lee, J. M., Riley, G. R., Jang, W., Rubinstein, W. S., Church, D. M., et al. (2014). ClinVar: public archive of relationships among sequence variation and human phenotype. Nucleic Acids Res. 42, D980–D985. Lim, K. P., Yip, S. P., Cheung, S. C., Leung, K. W., Lam, S. T., and To, C. H. (2009). Novel PRPF31 and PRPH2 mutations and co-occurrence of PRPF31 and RHO mutations in chinese patients with retinitis pigmentosa. Arch. Ophthalmol. 127, 784–790. Martin-Merida, I., Aguilera-Garcia, D., Fernandez-San Jose, P., Blanco-Kelly, F., Zurita, O., Almoguera, B., et al. (2018). Toward the mutational landscape of autosomal dominant retinitis pigmentosa: a comprehensive analysis of 258 spanish families. Invest. Ophthalmol. Vis. Sci. 59, 2345–2354. Mockel, A., Perdomo, Y., Stutzmann, F., Letsch, J., Marion, V., and Dollfus, H. (2011). Retinal dystrophy in Bardet-Biedl syndrome and related syndromic ciliopathies. Prog. Retin. Eye Res. 30, 258–274. Najera, C., Millan, J. M., Beneyto, M., and Prieto, F. (1995). Epidemiology of retinitis pigmentosa in the valencian community (Spain). Genet. Epidemiol. 12, 37–46. Rio Frio, T., Wade, N. M., Ransijn, A., Berson, E. L., Beckmann, J. S., and Rivolta, C. (2008). Premature termination codons in PRPF31 cause retinitis pigmentosa via haploinsufficiency due to nonsense-mediated mRNA decay. J. Clin. Invest. 118, 1519–1531. Schaffert, N., Hossbach, M., Heintzmann, R., Achsel, T., and Luhrmann, R. (2004). RNAi knockdown of hPrp31 leads to an accumulation of U4/U6 di-snRNPs in Cajal bodies. EMBO J. 23, 3000–3009. Sharon, D., and Banin, E. (2015). Nonsyndromic retinitis pigmentosa is highly prevalent in the jerusalem region with a high frequency of founder mutations. Mol. Vis. 21, 783–792. Sullivan, L. S., Bowne, S. J., Birch, D. G., Hughbanks-Wheaton, D., Heckenlively, J. R., Lewis, R. A., et al. (2006). 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, 3052–3064. Sullivan, L. S., Bowne, S. J., Reeves, M. J., Blain, D., Goetz, K., Ndifor, V., et al. (2013). Prevalence of mutations in eyeGENE probands with a diagnosis of autosomal dominant retinitis pigmentosa. Invest. Ophthalmol. Vis. Sci. 54, 6255–6261. doi: 10.1167/iovs.13-12605 Van Cauwenbergh, C., Coppieters, F., Roels, D., De Jaegere, S., Flipts, H., De Zaeytijd, J., et al. (2017). Mutations in splicing factor genes are a major cause of autosomal dominant retinitis pigmentosa in belgian families. PLoS One 12:e0170038. Verbakel, S. K., van Huet, R. A. C., Boon, C. J. F., den Hollander, A. I., Collin, R. W. J., Klaver, C. C. W., et al. (2018). Non-syndromic retinitis pigmentosa. Prog. Retin. Eye Res. 66, 157–186. Xu, F., Sui, R., Liang, X., Li, H., Jiang, R., and Dong, F. (2012). Novel PRPF31 mutations associated with chinese autosomal dominant retinitis pigmentosa patients. Mol. Vis. 18, 3021–3028. Zhang, Q., Xu, M., Verriotto, J. D., Li, Y., Wang, H., Gan, L., et al. (2016). Next-generation sequencing-based molecular diagnosis of 35 Hispanic retinitis pigmentosa probands. Sci. Rep. 6:32792.

Molecular Analysis and Detailed Phenotypic Study Abstract Purpose: To report novel variants and characterize the phenotype associated with the autosomal recessive retinal dystrophy caused by mutations in the lecithin retinol acyltransferase ( LRAT ) gene. Methods: A total of 149 patients with Leber's congenital amaurosis (LCA) or early onset retinal dystrophy were screened for mutations in LCA-associated genes using an arrayed-primer extension (APEX) genotyping microarray (Asper Ophthalmics). LRAT sequencing was subsequently performed in this 148-patient panel. Patients identified with mutations underwent further detailed phenotyping. Results: APEX analysis identified one patient with a previously reported homozygous LRAT mutation. Sequencing of the panel identified three additional patients with novel homozygous LRAT mutations in exon 2. All four patients had severe progressive nyctalopia, visual field constriction, and photophilia in childhood. Visual acuity ranged from 0.22 logMAR to hand motion. Funduscopy revealed severe retinal pigment epithelial atrophy and minimal retinal pigmentation. Asteroid hyalosis and macular epiretinal fibrosis were frequent. All demonstrated reduced fundus autofluorescence. Optical coherence tomography identified disrupted retinal lamination, outer-retinal debris, and an unidentifiable photoreceptor layer in two cases. Full-field electroretinograms were undetectable or showed severe rod-cone dysfunction. Photopic perimetry revealed severe visual field constriction. Dark-adapted perimetry demonstrated markedly reduced photoreceptor sensitivity. Dark-adapted spectral sensitivity measurements identified functioning rods in two of three patients. All three had severely reduced L- and M-cone sensitivity and poor color discrimination. Conclusions: LRAT mutations cause a severe, early childhood onset, progressive retinal dystrophy. Phenotypic similarities to the retinal dysfunction associated with RPE-specific protein 65 kDa mutations, another visual cycle gene, suggest that LRAT deficiency may show a good response to novel therapies. To read the entire article, click here . Investigative Ophthalmology & Visual Science June 2012, Vol.53, 3927-3938. doi: https://doi.org/10.1167/iovs.12-9548

Sawar Zahid MS, MD, Kari Branham MS, CGC, Dana Schlegel MS, MPH, CGC, Mark E. Pennesi MD, PhD, Michel Michaelides MB, MD, John Heckenlively MD & Thiran Jayasundera MD | Jun 26, 2018 | In: Retinal Dystrophy Gene Atlas | Abstract LRAT encodes lecithin retinol acyltransferase, which catalyzes the earlier reactions in the retinoid visual pathway in the retinal pigment epithelium (RPE). Recessive mutations in LRAT cause a spectrum of disease that ranges from Leber congenital amaurosis (LCA) to forms of “juvenile” or “early-onset” retinitis pigmentosa (RP) that present slightly later in life (1–3). Read the article: doi.org/10.1007/978-3-319-10867-4_44 References Thompson DA, Li Y, McHenry CL, Carlson TJ, Ding X, Sieving PA, et al. Mutations in the gene encoding lecithin retinol acyltransferase are associated with early-onset severe retinal dystrophy. National Genetics . 2001;28(2):123–4. Senechal A, Humbert G, Surget MO, Bazalgette C, Bazalgette C, Arnaud B, et al. Screening genes of the retinoid metabolism: novel LRAT mutation in leber congenital amaurosis. American Journal Ophthalmology . 2006; 142(4):702–4. den Hollander AI, Lopez I, Yzer S, Zonneveld MN, Janssen IM, Strom TM, et al. Identification of novel mutations in patients with Leber congenital amaurosis and juvenile RP by genome-wide homozygosity mapping with SNP microarrays. Invest Ophthalmology Vision Sciences . 2007 48(12):5690–8.

Céline Koster, Koen T. van den Hurk, Colby F. Lewallen, Mays Talib, Jacoline B. ten Brink, Camiel J. F. Boon, Arthur A. Bergen | International Journal of Molecular Sciences | July 5, 2021 | Vol. 22, Issue 13 | 7234 | doi: 10.3390/ijms22137234 Abstract Purpose: We developed and phenotyped a pigmented knockout rat model for lecithin retinol acyltransferase (LRAT) using CRISPR/Cas9. The introduced mutation (c.12delA) is based on a patient group harboring a homologous homozygous frameshift mutation in the LRAT gene (c.12delC), causing a dysfunctional visual (retinoid) cycle. Methods: The introduced mutation was confirmed by DNA and RNA sequencing. The expression of Lrat was determined on both the RNA and protein level in wildtype and knockout animals using RT-PCR and immunohistochemistry. The retinal structure and function, as well as the visual behavior of the Lrat −/− and control rats, were characterized using scanning laser ophthalmoscopy (SLO), optical coherence tomography (OCT), electroretinography (ERG) and vision-based behavioral assays. Results: Wildtype animals had high Lrat mRNA expression in multiple tissues, including the eye and liver. In contrast, hardly any expression was detected in Lrat −/− animals. LRAT protein was abundantly present in wildtype animals and absent in Lrat −/− animals. Lrat −/− animals showed progressively reduced ERG potentials compared to wildtype controls from two weeks of age onwards. Vison-based behavioral assays confirmed reduced vision. Structural abnormalities, such as overall retinal thinning, were observed in Lrat −/− animals. The retinal thickness in knockout rats was decreased to roughly 80% by four months of age. No functional or structural differences were observed between wildtype and heterozygote animals. Conclusions: Our Lrat −/− rat is a new animal model for retinal dystrophy, especially for the LRAT -subtype of early-onset retinal dystrophies. This model has advantages over the existing mouse models and the RCS rat strain and can be used for translational studies of retinal dystrophies. Introduction Retinitis pigmentosa (RP), Leber congenital amaurosis (LCA), and retinitis punctata albescens (RPA) are severe early-onset retinal dystrophies that cause visual impairment, nystagmus, progressive nyctalopia, and finally, blindness. This heterogeneous retinal dystrophy disease group is characterized by damage to the retinal pigment epithelium (RPE)–photoreceptor (PR) complex. This results usually in progressive dysfunction of the rod photoreceptor cells, often followed by progressive cone degeneration. RP, LCA, and RPA are caused by mutations in virtually all genes encoding proteins acting in the retinoid cycle ( 1 , 2 , 3 , 4 ). Indeed, for normal vision, a functionally valid retinoid cycle is essential: In the healthy situation, vitamin A (retinol) is the primary substrate for several functional retinoids’ biosynthesis in the retinoid cycle. Then, the vitamin A-derivatives are shuttled from the RPE to the PRs. There, opsins are light-activated and the visual pigments transform the light energy in a cellular signal, initiating the visual cascade and resulting in a physiological response in the PR cell. After light activation, the cycle regenerates the visual pigments that are used after light activation of rhodopsin (see Figure 1 ). Upon photoactivation, a configurational change of the visual pigment 11- cis -retinal to all- trans -retinal is induced in the PR cells’ outer segments. Subsequently, all- trans -retinal is reduced to all- trans -retinol and diffuses from the PRs back to to the RPE cells. In the RPE, all- trans -retinol is esterified to all- trans -retinyl-ester by the enzyme lecithin:retinol acetyltransferase (LRAT), after which all- trans -retinyl-ester is subsequently the substrate for the enzyme retinal pigment epithelium-specific protein 65 kDa (RPE65). RPE65 converts all- trans -retinyl-ester to 11- cis -retinol, after which 11- cis -retinol is oxidized by retinol dehydrogenase (RDH) enzymes to 11- cis -retinal. Finally, to complete the cycle, 11- cis -retinal is shuttled back to the PRs, where it can be used for a new round of phototransduction. Read the article References 1. Chelstowska S., Widjaja-Adhi M.A.K., Silvaroli J.A., Golczak M. Impact of LCA-Associated E14L LRAT Mutation on Protein Stability and Retinoid Homeostasis. Biochemistry. 2017;56:4489–4499. doi: 10.1021/acs.biochem.7b00451. 2. Den Hollander A.I., Lopez I., Yzer S., Zonneveld M.N., Janssen I.M., Strom T.M., Hehir-Kwa J.Y., Veltman J.A., Arends M.L., Meitinger T., et al. Identification of novel mutations in patients with Leber congenital amaurosis and juvenile RP by genome-wide homozygosity mapping with SNP microarrays. Investig. Ophthalmol. Vis. Sci. 2007;48:5690–5698. doi: 10.1167/iovs.07-0610. 3. Dev Borman A., Ocaka L.A., Mackay D.S., Ripamonti C., Henderson R.H., Moradi P., Hall G., Black G.C., Robson A.G., Holder G.E., et al. Early onset retinal dystrophy due to mutations in LRAT: Molecular analysis and detailed phenotypic study. Investig. Ophthalmol. Vis. Sci. 2012;53:3927–3938. doi: 10.1167/iovs.12-9548. 4. Littink K.W., van Genderen M.M., van Schooneveld M.J., Visser L., Riemslag F.C., Keunen J.E., Bakker B., Zonneveld M.N., den Hollander A.I., Cremers F.P., et al. A homozygous frameshift mutation in LRAT causes retinitis punctata albescens. Ophthalmology. 2012;119:1899–1906. doi: 10.1016/j.ophtha.2012.02.037.

By Jeff Hansen | June 10, 2020 Researchers who made a knock-in mouse-model of the genetic disorder retinitis pigmentosa 59, or RP59, expected to see retinal degeneration and retinal thinning. As reported in the journal Cells, they surprisingly found none, calling into question the commonly accepted — though never proved — mechanism for RP59. “Our findings bring into question the current concept that RP59 is a member of a large and diverse class of diseases known as ‘congenital disorders of glycosylation,’” said Steven Pittler, Ph.D., professor and director of the University of Alabama at Birmingham School of Optometry and Vision Science Vision Science Research Center. “While in principle it would be reasonable to consider RP59 as a congenital disorder of glycosylation, due to the associated mutation in DHDDS, an enzyme required for glycosylation, there is no direct evidence to demonstrate a glycosylation defect in the human retinal disease or in any animal model of RP59 generated to date.” Read the article Researchers at UAB, SUNY-Buffalo and the Polish Academy of Sciences did the study.

Byron L Lam, Stephan L Züchner, Julia Dallman, Rong Wen, Eduardo C Alfonso, Jeffery M Vance, Margaret A Peričak-Vance |  Advances in Experimental Medicine and Biology  book series |  2014 Jan 1 | vol. 801 | 165-70 | doi: 10.1007/978-1-4614-3209-8_21 A single-nucleotide mutation in the gene that encodes DHDDS has been identified by whole exome sequencing as the cause of the non-syndromic recessive retinitis pigmentosa (RP) in a family of Ashkenazi Jewish origin in which three of the four siblings have early onset retinal degeneration. The peripheral retinal degeneration in the affected siblings was evident in the initial examination in 1992 and only one had detectable electroretinogram (ERG) that suggested cone-rod dysfunction. Read more, click here

Isabelle Perrault , Jean-Michel Rozet , Sylvie Gerber , Imad Ghazi , Corinne Leowski , Dominique Ducroq , Eric Souied , Jean-Louis Dufier , Arnold Munnich , Josseline Kaplan | Molecular Genetics and Metabolism | Volume 68, Issue 2 | October 1999 | Pages 200-208 Abstract Leber's congenital amaurosis (LCA) is the earliest and most severe form of all inherited retinal dystrophies responsible for congenital blindness. Genetic heterogeneity of LCA has been suspected since the report by Waardenburg of normal children born to affected parents. In 1995, we localized the first disease causing gene, LCA1, to chromosome 17p13 and confirmed the genetic heterogeneity. In 1996, we ascribed LCA1 to mutations in the photoreceptor-specific guanylate cyclase gene (retGC1). RetGC1 is an essential protein implicated in the phototransduction cascade, especially in the recovery of the dark state after the excitation process of photoreceptor cells by light stimulation. In 1997, mutations in a second gene were reported in LCA, the RPE65 gene, which is the first specific retinal pigment epithelium gene. The protein RPE65 is implicated in the metabolism of vitamin A, the precursor of the photoexcitable retinal pigment (rhodopsin). Finally, a third gene, CRX, implicated in photoreceptor development, has been suspected of causing a few cases of LCA. Taken together, these three genes account for only 27% of LCA cases in our series. The three genes encode proteins that are involved in completely different physiopathologic pathways. Based on these striking differences of physiopathologic processes, we reexamined all clinical physiopathological discrepancies and the results strongly suggested that retGC1 gene mutations are responsible for congenital stationary severe cone–rod dystrophy, while RPE65 gene mutations are responsible for congenital severe but progressive rod–cone dystrophy. It is of tremendous importance to confirm and to refine these genotype–phenotype correlations on a large scale in order to anticipate the final outcome in a blind infant, on the one hand, and to further guide genetic studies in older patients on the other hand. To purchase paper, follow this link