Heterozygous deletions of noncoding parts of the PRPF31 gene cause retinitis pigmentosa via reduced gene expression.

Purpose: Heterozygous mutations in the gene PRPF31, encoding a pre-mRNA splicing factor, cause autosomal dominant retinitis pigmentosa (adRP) with reduced penetrance. At the molecular level, pathogenicity results from haploinsufficiency, as the largest majority of such mutations trigger nonsense-mediated mRNA decay or involve large deletions of coding exons. We investigated genetically two families with a history of adRP, one of whom showed incomplete penetrance. Methods: All patients underwent thorough ophthalmological examination, including electroretinography (ERG) and Goldmann perimetry. Array-based comparative genomic hybridization (aCGH) and multiplex ligation-dependent probe amplification (MLPA) were used to map heterozygous deletions, while real-time PCR on genomic DNA and long-range PCR allowed resolving the mutations at the base-pair level. PRPF31 transcripts were quantified with real-time PCR on patient-derived lymphoblastoid cell lines. Results: We identified two independent deletions affecting the promoter and the 5' untranslated region (UTR) of PRPF31 but leaving its coding sequence completely unaltered. Analysis of PRPF31 mRNA from lymphoblastoid cell lines from one of these families showed reduced levels of expression in patients versus controls, probably due to the heterozygous ablation of its promoter sequences. Conclusions: In addition to reporting the identification of two novel noncoding deletions in PRPF31, this study provides strong additional evidence that mRNA-mediated haploinsufficiency is the primary cause of pathogenesis for PRPF31-linked adRP.

Variable phenotype of Knobloch syndrome due to biallelic COL18A1 mutations in children.

PURPOSE: Knobloch syndrome is a rare, recessively inherited disorder classically characterized by high myopia, retinal detachment, and occipital encephalocele. Our aim is to report the clinical and genetic findings of four Israeli children affected by Knobloch syndrome. METHODS: Retrospective study of four patients diagnosed with Knobloch syndrome, who underwent full ophthalmic examination, electroretinography, and neuroradiologic imaging. Genetic analysis included whole exome sequencing (WES) and Sanger sequencing. RESULTS: The four patients included in this study had high myopia and nystagmus at presentation. Ocular findings included vitreous syneresis, macular atrophy, macular coloboma, and retinal detachment. One child had iris transillumination defects and an albinotic fundus, initially leading to an erroneous clinical diagnosis of albinism. Electroretinography revealed a marked cone-rod pattern of dysfunction in all four children. Brain imaging demonstrated none to severe occipital pathology. Cutaneous scalp changes were present in three patients. WES analysis, confirmed by Sanger sequencing revealed COL18A1 biallelic null mutations in all affected individuals, consistent with autosomal recessive inheritance. CONCLUSIONS: This report describes variable features in patients with Knobloch syndrome, including marked lack of eye pigment similar to albinism in one child, macular coloboma in two children as well as advanced cone-rod dysfunction in all children. One patient had normal neuroradiologic findings, emphasizing that some affected individuals have isolated ocular disease. Awareness of this syndrome, with its variable phenotype may aid early diagnosis, monitoring for potential complications, and providing appropriate genetic counseling.

Progressive Visual Loss Without Retinal Detachment in Stickler Syndrome: An Uncommon and Novel Presentation.

Stickler syndrome is known to cause visual handicap due to the high incidence of retinal detachment. We aim to present an unusual case of a child with Stickler syndrome who had progressive visual loss secondary to atrophy of the outer retinal layers not associated with retinal detachment. This is a descriptive case report of a 9-year-old child with ocular history of high myopia who presented to our institution with suboptimal visual acuity in both eyes. After 2 years of follow up, he developed unilateral progressive visual loss with marked atrophy of the outer retinal layers and peripheral vascular leakage. Such a presentation has not been previously described in the literature to the best of our knowledge.

An Ashkenazi Jewish founder mutation in CACNA1F causes retinal phenotype in both hemizygous males and heterozygous female carriers.

Background: Mutations in CACNA1F have been mainly associated with X-linked incomplete congenital stationary night blindness (icCSNB). Variable phenotypic expression in females was reported in some families. We report here three non-related Ashkenazi Jewish families originating in Eastern Europe, that included males and a many affected females, initially diagnosed with variable retinal phenotypes.Materials and Methods: Whole exome sequencing (WES), Sanger sequencing and microsatellite haplotyping were used for genetic analysis. Complete ophthalmologic examination was performed including visual acuity, refraction, colour vision, slit-lamp, fundoscopy and electroretinography (ERG).Results: We identified four affected males, showing moderate visual impairment, and seven female carriers, six of them presenting mild to moderate visual impairment. Infantile nystagmus was found in all affected males and in 5/7 females. Nyctalopia and myopia were common in both males and females. Initial clinical differential diagnosis included cone-dystrophy, cone-rod dystrophy, cone-dystrophy with supernormal rod response or CSNB based on ERG results. WES and Sanger sequencing revealed a previously described missense mutation c.2225T>G; p.(F742C) in CACNA1F (NM_001256789.2) in all three families, encompassed by a shared haplotypeConclusions: Our data suggests that p.(F742C) in CACNA1F is an X-linked founder mutation in Ashkenazi Jews originating in Eastern Europe. This mutation causes a mild-to-moderate icCSNB phenotype, expressed in most female carriers. A targeted test for this variant in suspected patients may initiate diagnostic analysis. Our results highlight the relevance of WES in the clinic, allowing fast and accurate diagnosis for unclear and variable clinical phenotype and in pedigrees with multiple possible inheritance patterns.

Carrier frequency analysis of mutations causing autosomal-recessive-inherited retinal diseases in the Israeli population.

Inherited retinal diseases (IRDs) are heterogeneous phenotypes caused by variants in a large number of genes. Disease prevalence and the frequency of carriers in the general population have been estimated in only a few studies, but are largely unknown. To this end, we developed two parallel methods to calculate carrier frequency for mutations causing autosomal-recessive (AR) IRDs in the Israeli population. We created an SQL database containing information on 178 genes from gnomAD (including genotyping of 5706 Ashkenazi Jewish (AJ) individuals) and our cohort of >2000 families with IRDs. Carrier frequency for IRD variants and genes was calculated based on allele frequency values and the Hardy-Weinberg (HW) equation. We identified 399 IRD-causing variants in 111 genes in Israeli patients and AJ controls. For the AJ subpopulation, gnomAD and HW-based regression analysis showed high correlation, therefore allowing one to use HW-based data as a reliable estimate of carrier frequency. Overall, carrier frequency per subpopulation ranges from 1/2.2 to 1/9.6 individuals, with the highest value obtained for the Arab-Muslim subpopulation in Jerusalem reaching an extremely high carrier rate of 44.7%. Carrier frequency per gene ranges from 1/31 to 1/11994 individuals. We estimate the total carrier frequency for AR-IRD mutations in the Israeli population as over 30%, a relatively high carrier frequency with marked variability among subpopulations. Therefore, these data are highly important for more reliable genetic counseling and genetic screening. Our method can be adapted to study other populations, either based on allele frequency data or cohort of patients.

Nonsyndromic Retinitis Pigmentosa in the Ashkenazi Jewish Population: Genetic and Clinical Aspects.

PURPOSE: To analyze the genetic and clinical findings in retinitis pigmentosa (RP) patients of Ashkenazi Jewish (AJ) descent, aiming to identify genotype-phenotype correlations. DESIGN: Cohort study. PARTICIPANTS: Retinitis pigmentosa patients from 230 families of AJ origin. METHODS: Sanger sequencing was performed to detect specific founder mutations known to be prevalent in the AJ population. Ophthalmologic analysis included a comprehensive clinical examination, visual acuity (VA), visual fields, electroretinography, color vision testing, and retinal imaging by OCT, pseudocolor, and autofluorescence fundus photography. MAIN OUTCOME MEASURES: Inheritance pattern and causative mutation; retinal function as assessed by VA, visual fields, and electroretinography results; and retinal structural changes observed on clinical funduscopy as well as by pseudocolor, autofluorescence, and OCT imaging. RESULTS: The causative mutation was identified in 37% of families. The most prevalent RP-causing mutations are the Alu insertion (c.1297_8ins353, p.K433Rins31*) in the male germ cell-associated kinase (MAK) gene (39% of families with a known genetic cause for RP) and c.124A>G, p.K42E in dehydrodolichol diphosphate synthase (DHDDS) (33%). Additionally, disease-causing mutations were identified in 11 other genes. Analysis of clinical parameters of patients with mutations in the 2 most common RP-causing genes revealed that MAK patients had better VA and visual fields at relatively older ages in comparison with DHDDS patients. Funduscopic findings of DHDDS patients matched those of MAK patients who were 20 to 30 years older. Patients with DHDDS mutations were referred for electrophysiologic evaluation at earlier ages, and their cone responses became nondetectable at a much younger age than MAK patients. CONCLUSIONS: Our AJ cohort of RP patients is the largest reported to date and showed a substantial difference in the genetic causes of RP compared with cohorts of other populations, mainly a high rate of autosomal recessive inheritance and a unique composition of causative genes. The most common RP-causing genes in our cohort, MAK and DHDDS, were not described as major causative genes in other populations. The clinical data show that in general, patients with biallelic MAK mutations had a later age of onset and a milder retinal phenotype compared with patients with biallelic DHDDS mutations.

Whole-Exome Sequencing Identifies Biallelic IDH3A Variants as a Cause of Retinitis Pigmentosa Accompanied by Pseudocoloboma.

PURPOSE: To identify the genetic cause of and describe the phenotype in 4 families with autosomal recessive retinitis pigmentosa (arRP) that can be associated with pseudocoloboma. DESIGN: Case series. PARTICIPANTS: Seven patients from 4 unrelated families with arRP, among whom 3 patients had bilateral early-onset macular pseudocoloboma. METHODS: We performed homozygosity mapping and whole-exome sequencing in 5 probands and 2 unaffected family members from 4 unrelated families. Subsequently, Sanger sequencing and segregation analysis were performed in additional family members. We reviewed the medical history of individuals carrying IDH3A variants and performed additional ophthalmic examinations, including full-field electroretinography, fundus photography, fundus autofluorescence imaging, and optical coherence tomography. MAIN OUTCOME MEASURES: IDH3A variants, age at diagnosis, visual acuity, fundus appearance, visual field, and full-field electroretinography, fundus autofluorescence, and optical coherence tomography findings. RESULTS: We identified 7 different variants in IDH3A in 4 unrelated families, that is, 5 missense, 1 nonsense, and 1 frameshift variant. All participants showed symptoms early in life, ranging from night blindness to decreased visual acuity, and were diagnosed between the ages of 1 and 11 years. Four participants with biallelic IDH3A variants displayed a typical arRP phenotype and 3 participants were diagnosed with arRP and pseudocoloboma of the macula. CONCLUSIONS: IDH3A variants were identified as a novel cause of typical arRP in some individuals associated with macular pseudocoloboma. We observed both phenotypes in 2 siblings carrying the same compound heterozygous variants, which could be explained by variable disease expression and warrants caution when making assertions about genotype-phenotype correlations.

A missense mutation in ASRGL1 is involved in causing autosomal recessive retinal degeneration.

Inherited retinal dystrophies are a group of genetically heterogeneous conditions with broad phenotypic heterogeneity. We analyzed a large five-generation pedigree with early-onset recessive retinal degeneration to identify the causative mutation. Linkage analysis and homozygosity mapping combined with exome sequencing were carried out to map the disease locus and identify the p.G178R mutation in the asparaginase like-1 gene (ASRGL1), segregating with the retinal dystrophy phenotype in the study pedigree. ASRGL1 encodes an enzyme that catalyzes the hydrolysis of L-asparagine and isoaspartyl-peptides. Studies on the ASRGL1 expressed in Escherichia coli and transiently transfected mammalian cells indicated that the p.G178R mutation impairs the autocatalytic processing of this enzyme resulting in the loss of functional ASRGL1 and leaving the inactive precursor protein as a destabilized and aggregation-prone protein. A zebrafish model overexpressing the mutant hASRGL1 developed retinal abnormalities and loss of cone photoreceptors. Our studies suggest that the p.G178R mutation in ASRGL1 leads to photoreceptor degeneration resulting in progressive vision loss.

Mutations in POMGNT1 cause non-syndromic retinitis pigmentosa.

A growing number of human diseases have been linked to defects in protein glycosylation that affects a wide range of organs. Among them, O-mannosylation is an unusual type of protein glycosylation that is largely restricted to the muscular and nerve system. Consistently, mutations in genes involved in the O-mannosylation pathway result in infantile-onset, severe developmental defects involving skeleton muscle, brain and eye, such as the muscle-eye-brain disease (MIM no. 253280). However, the functional importance of O-mannosylation in these tissues at later stages remains largely unknown. In our study, we have identified recessive mutations in POMGNT1, which encodes an essential component in O-mannosylation pathway, in three unrelated families with autosomal recessive retinitis pigmentosa (RP), but without extraocular involvement. Enzymatic assay of these mutant alleles demonstrate that they greatly reduce the POMGNT1 enzymatic activity and are likely to be hypomorphic. Immunohistochemistry shows that POMGNT1 is specifically expressed in photoreceptor basal body. Taken together, our work identifies a novel disease-causing gene for RP and indicates that proper protein O-mannosylation is not only essential for early organ development, but also important for maintaining survival and function of the highly specialized retinal cells at later stages.

OR2W3 sequence variants are unlikely to cause inherited retinal diseases.

Because of its formidable throughput, whole exome sequencing (WES) is significantly increasing the power of investigations in ophthalmic genetics. However, when applied to Mendelian conditions, WES results often contain many false positives, e.g. candidate mutations that are unrelated to the disease. For instance, highly polymorphic genes such as olfactory receptor genes carry a plethora of both common and rare alleles that are part of the normal set of variations of the human genome. Following a WES-based study, the heterozygous missense variant p.R142W in the olfactory receptor gene OR2W3 was recently reported as a pathogenic mutation causing autosomal dominant retinitis pigmentosa (RP). This variant, however, was not scored against data contained in public WES repositories, indicating that p.R142W is present in ~1 in 6500 control individuals. Therefore, if it really was pathogenic, it would be responsible for a percentage of dominant RP cases corresponding to the double of those recorded so far worldwide, or 2/3 of all RP cases (dominant, recessive, and X-linked). We therefore conclude that this sequence variant, and hence the OR2W3 gene, do not cause RP. Prompted by these findings and based on simple principles of population genetics, we suggest that WES studies should consider DNA variants as the possible cause of dominant RP only if they are present in less than 1:100,000 individuals from the general population. In addition, we propose that DNA variants belonging to highly polymorphic genes should be carefully analyzed at the functional level before inferring their pathogenicity, in RP or other genetic diseases.

Whole Exome Sequencing Reveals Mutations in Known Retinal Disease Genes in 33 out of 68 Israeli Families with Inherited Retinopathies.

Whole exome sequencing (WES) is a powerful technique for identifying sequence changes in the human genome. The goal of this study was to delineate the genetic defects in patients with inherited retinal diseases (IRDs) using WES. WES was performed on 90 patient DNA samples from 68 families and 226 known genes for IRDs were analyzed. Sanger sequencing was used to validate potential pathogenic variants that were also subjected to segregation analysis in families. Thirty-three causative mutations (19 novel and 14 known) in 25 genes were identified in 33 of the 68 families. The vast majority of mutations (30 out of 33) have not been reported in the Israeli and the Palestinian populations. Nine out of the 33 mutations were detected in additional families from the same ethnic population, suggesting a founder effect. In two families, identified phenotypes were different from the previously reported clinical findings associated with the causative gene. This is the largest genetic analysis of IRDs in the Israeli and Palestinian populations to date. We also demonstrate that WES is a powerful tool for rapid analysis of known disease genes in large patient cohorts.

Nonsyndromic Early-Onset Cone-Rod Dystrophy and Limb-Girdle Muscular Dystrophy in a Consanguineous Israeli Family are Caused by Two Independent yet Linked Mutations in ALMS1 and DYSF.

Genetic analysis of clinical phenotypes in consanguineous families is complicated by coinheritance of large DNA regions carrying independent variants. Here, we characterized a family with early onset cone-rod dystrophy (CRD) and muscular dystrophy. Homozygosity mapping (HM) followed by whole exome sequencing revealed a nonsense mutation, p.R270*, in ALMS1 and two novel potentially disease-causing missense variants, p.R1581C and p.Y2070C, in DYSF. ALMS1 and DYSF are genetically and physically linked on chromosome 2 in a genomic region suggested by HM and associated with Alström syndrome, which includes CRD, and with limb girdle muscular dystrophy, respectively. Affected family members lack additional systemic manifestations of Alström syndrome but exhibit mild muscular dystrophy. RNA-seq data did not reveal any significant variations in ALMS1 transcripts in the human retina. Our study thus implicates ALMS1 as a nonsyndromic retinal disease gene and suggests a potential role of variants in interacting cilia genes in modifying clinical phenotypes.

Whole exome sequencing reveals GUCY2D as a major gene associated with cone and cone-rod dystrophy in Israel.

PURPOSE: The Israeli population has a unique genetic make-up, with a high prevalence of consanguineous marriages and autosomal recessive diseases. In rod-dominated phenotypes, disease-causing genes and mutations that differ from those identified in other populations often are incurred. We used whole exome sequencing (WES) to identify genetic defects in Israeli families with cone-dominated retinal phenotypes. METHODS: Clinical analysis included family history, detailed ocular examination, visual function testing, and retinal imaging. Whole exome sequencing, followed by segregation analysis, was performed in 6 cone-dominated retinopathy families in which prior mutation analysis did not reveal the causative gene. Based on the WES findings, we screened 106 additional families with cone-dominated phenotypes. RESULTS: The WES analysis revealed mutations in known retinopathy genes in five of the six families: two pathogenic mutations in the GUCY2D gene in three families, and one each in CDHR1 and C8orf37. Targeted screening of additional cone-dominated families led to identification of GUCY2D mutations in four other families, which included two highly probable novel disease-causing variants. CONCLUSIONS: Our study suggested that GUCY2D is a major cause of autosomal dominant cone and cone-rod dystrophies in Israel; this is similar to other Caucasian populations and is in contrast with retinitis pigmentosa (primary rod disease), where the genetic make-up of the Israeli population is distinct from other ethnic groups. We also conclude that WES permits more comprehensive and rapid analyses that can be followed by targeted screens of larger samples to delineate the genetic structure of retinal disease in unique population cohorts.