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Around 60% of individuals with neurodevelopmental disorders (NDD) remain undiagnosed after comprehensive genetic testing, primarily of protein-coding genes 1 . Large genome-sequenced cohorts are improving our ability to discover new diagnoses in the non-coding genome. Here we identify the non-coding RNA RNU4-2 as a syndromic NDD gene. RNU4-2 encodes the U4 small nuclear RNA (snRNA), which is a critical component of the U4/U6.U5 tri-snRNP complex of the major spliceosome 2 . We identify an 18 base pair region of RNU4-2 mapping to two structural elements in the U4/U6 snRNA duplex (the T-loop and stem III) that is severely depleted of variation in the general population, but in which we identify heterozygous variants in 115 individuals with NDD. Most individuals (77.4%) have the same highly recurrent single base insertion (n.64_65insT). In 54 individuals in whom it could be determined, the de novo variants were all on the maternal allele. We demonstrate that RNU4-2 is highly expressed in the developing human brain, in contrast to RNU4-1 and other U4 homologues. Using RNA sequencing, we show how 5' splice-site use is systematically disrupted in individuals with RNU4-2 variants, consistent with the known role of this region during spliceosome activation. Finally, we estimate that variants in this 18 base pair region explain 0.4% of individuals with NDD. This work underscores the importance of non-coding genes in rare disorders and will provide a diagnosis to thousands of individuals with NDD worldwide., (© 2024. The Author(s).)

Retinol dehydrogenase 12 (RDH12) is expressed in photoreceptor inner segments and catalyses the reduction of all-trans retinal (atRAL) to all-trans retinol (atROL), as part of the visual cycle. Mutations in RDH12 are primarily associated with autosomal recessive Leber congenital amaurosis. To further our understanding of the disease mechanisms, HEK-293 cell lines expressing wildtype (WT) and mutant RDH12 were created. The WT cells afforded protection from atRAL-induced toxicity and oxidative stress. Mutant RDH12 cells displayed reduced protein expression and activity, with an inability to protect cells from atRAL toxicity, inducing oxidative and endoplasmic reticulum (ER) stress, with upregulation of sXBP1 , CHOP , and ATF4 . Pregabalin, a retinal scavenger, attenuated atRAL-induced ER stress in the mutant RDH12 cell lines. A zebrafish rdh12 mutant model ( rdh12 u533 c.17_23del; p.(Val6AlafsTer5)) was generated through CRISPR-Cas9 gene editing. Mutant fish showed disrupted phagocytosis through transmission electron microscopy, with increased phagosome size at 12 months post-fertilisation. Rhodopsin mislocalisation and reduced expression of atg12 and sod2 indicated early signs of a rod-predominant degeneration. A lack of functional RDH12 results in ER and oxidative stress representing key pathways to be targeted for potential therapeutics.

Albinism encompasses a group of hereditary disorders characterized by reduced or absent ocular pigment and variable skin and/or hair involvement, with syndromic forms such as Hermansky-Pudlak syndrome and Chédiak-Higashi syndrome. Autosomal recessive oculocutaneous albinism (OCA) is phenotypically and genetically heterogenous (associated with seven genes). X-linked ocular albinism (OA) is associated with only one gene, GPR143 . We report the clinical and genetic outcomes of 44 patients, from 40 unrelated families of diverse ethnicities, with query albinism presenting to the ocular genetics service at Moorfields Eye Hospital NHS Foundation Trust between November 2017 and October 2019. Thirty-six were children (≤ 16 years) with a median age of 31 months (range 2-186), and eight adults with a median age of 33 years (range 17-39); 52.3% ( n = 23) were male. Genetic testing using whole genome sequencing (WGS, n = 9) or a targeted gene panel ( n = 31) gave an overall diagnostic rate of 42.5% (44.4% (4/9) with WGS and 41.9% (13/31) with panel testing). Seventeen families had confirmed mutations in TYR ( n = 9), OCA2 , ( n = 4), HPS1 ( n = 1), HPS3 ( n = 1), HPS6 ( n = 1), and GPR143 ( n = 1). Molecular diagnosis of albinism remains challenging due to factors such as missing heritability. Differential diagnoses must include SLC38A8 -associated foveal hypoplasia and syndromic forms of albinism.

Biallelic pathogenic variants in solute carrier family 38 member 8, SLC38A8 , cause a pan-ocular autosomal recessive condition known as foveal hypoplasia 2, FVH2, characterised by foveal hypoplasia, nystagmus and optic nerve chiasmal misrouting. Patients are often clinically diagnosed with ocular albinism, but foveal hypoplasia can occur in several other ocular disorders. Here we describe nine patients from seven families who had molecularly confirmed biallelic recessive variants in SLC38A8 identified through whole genome sequencing or targeted gene panel testing. We identified four novel sequence variants (p.(Tyr88*), p.(Trp145*), p.(Glu233Gly) and c.632+1G>A). All patients presented with foveal hypoplasia, nystagmus and reduced visual acuity; however, one patient did not exhibit any signs of chiasmal misrouting, and three patients had features of anterior segment dysgenesis. We highlight these findings in the context of 30 other families reported to date. This study reinforces the importance of obtaining a molecular diagnosis in patients whose phenotype overlap with other inherited ocular conditions, in order to support genetic counselling, clinical prognosis and family planning. We expand the spectrum of SLC38A8 mutations which will be relevant for treatment through future genetic-based therapies.

Bilallelic variants in the USH2A gene can cause Usher syndrome type 2 and non-syndromic retinitis pigmentosa. In both disorders, the retinal phenotype involves progressive rod photoreceptor loss resulting in nyctalopia and a constricted visual field, followed by subsequent cone degeneration, leading to the loss of central vision and severe visual impairment. The USH2A gene raises many challenges for researchers and clinicians due to a broad spectrum of mutations, a large gene size hampering gene therapy development and limited knowledge on its pathogenicity. Patients with Usher type 2 may benefit from hearing aids or cochlear implants to correct their hearing defects, but there are currently no approved treatments available for the USH2A-retinopathy. Several treatment strategies, including antisense oligonucleotides and translational readthrough inducing drugs, have shown therapeutic promise in preclinical studies. Further understanding of the pathogenesis and natural history of USH2A-related disorders is required to develop innovative treatments and design clinical trials based on reliable outcome measures. The present review will discuss the current knowledge about USH2A, the emerging therapeutics and existing challenges., (Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Purpose: In a large cohort of molecularly characterized inherited retinal disease (IRD) families, we investigated proportions with disease attributable to causative variants in each gene., Design: Retrospective study of electronic patient records., Participants: Patients and relatives managed in the Genetics Service of Moorfields Eye Hospital in whom a molecular diagnosis had been identified., Methods: Genetic screening used a combination of single-gene testing, gene panel testing, whole exome sequencing, and more recently, whole genome sequencing. For this study, genes listed in the Retinal Information Network online resource (https://sph.uth.edu/retnet/) were included. Transcript length was extracted for each gene (Ensembl, release 94)., Main Outcome Measures: We calculated proportions of families with IRD attributable to variants in each gene in the entire cohort, a cohort younger than 18 years, and a current cohort (at least 1 patient encounter between January 1, 2017, and August 2, 2019). Additionally, we explored correlation between numbers of families and gene transcript length., Results: We identified 3195 families with a molecular diagnosis (variants in 135 genes), including 4236 affected individuals. The pediatric cohort comprised 452 individuals from 411 families (66 genes). The current cohort comprised 2614 families (131 genes; 3130 affected individuals). The 20 most frequently implicated genes overall (with prevalence rates per families) were as follows: ABCA4 (20.8%), USH2A (9.1%), RPGR (5.1%), PRPH2 (4.6%), BEST1 (3.9%), RS1 (3.5%), RP1 (3.3%), RHO (3.3%), CHM (2.7%), CRB1 (2.1%), PRPF31 (1.8%), MY07A (1.7%), OPA1 (1.6%), CNGB3 (1.4%), RPE65 (1.2%), EYS (1.2%), GUCY2D (1.2%), PROM1 (1.2%), CNGA3 (1.1%), and RDH12 (1.1%). These accounted for 71.8% of all molecularly diagnosed families. Spearman coefficients for correlation between numbers of families and transcript length were 0.20 (P = 0.025) overall and 0.27 (P = 0.017), -0.17 (P = 0.46), and 0.71 (P = 0.047) for genes in which variants exclusively cause recessive, dominant, or X-linked disease, respectively., Conclusions: Our findings help to quantify the burden of IRD attributable to each gene. More than 70% of families showed pathogenic variants in 1 of 20 genes. Transcript length (relevant to gene delivery strategies) correlated significantly with numbers of affected families (but not for dominant disease)., (Copyright © 2020 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.)

Aims: Using optical coherence tomography angiography (OCTA) to characterise microvascular changes in the retinal plexuses and choriocapillaris (CC) of patients with MYO7A and USH2A mutations and correlate with genotype, retinal structure and function., Methods: Twenty-seven patients with molecularly confirmed USH2A (n=21) and MYO7A (n=6) mutations underwent macular 6×6 mm OCTA using the AngioVue. Heidelberg spectral-domain OCT scans and MAIA microperimetry were also performed, the preserved ellipsoid zone (EZ) band width and mean macular sensitivity (MS) were recorded. OCTA of the inner retina, superficial capillary plexus (SCP), deep capillary plexus (DCP) and CC were analysed. Vessel density (VD) was calculated from the en face OCT angiograms of retinal circulation., Results: Forty-eight eyes with either USH2A (n=37, mean age: 34.4±12.2 years) or MYO7A (n=11, mean age: 37.1±12.4 years), and 35 eyes from 18 age-matched healthy participants were included. VD was significantly decreased in the retinal circulation of patients with USH2A and MYO7A mutations compared with controls (p<0.001). Changes were observed in both the SCP and DCP, but no differences in retinal perfusion were detected between USH2A and MYO7A groups. No vascular defects were detected in CC of the USH2A group, but peripheral defects were detected in older MYO7A patients from the fourth decade of life. VD in the DCP showed strong association with MS and EZ width (Spearman's rho =0.64 and 0.59, respectively, p<0.001)., Conclusion: OCTA was able to detect similar retinal microvascular changes in patients with USH2A and MYO7A mutations. The CC was generally affected in MYO7A mutations. OCT angiography may further enhance our understanding of inherited eye diseases and their phenotype-genotype associations., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2020. No commercial re-use. See rights and permissions. Published by BMJ.)

Name of the disease (synonyms) See Table 1, Column 1-"Name of disease" and Column 2-"Alternative names". OMIM# of the disease See Table 1, Column 3-"OMIM# of the disease". Name of the analysed genes or DNA/chromosome segments and OMIM# of the gene(s) Core genes (irrespective of being tested by Sanger sequencing or next-generation sequencing): See Table 1, Column 4-"Cytogenetic location", Column 5-"Associated gene(s)" and Column 6-"OMIM# of associated gene(s)". Additional genes (if tested by next-generation sequencing, including Whole exome/genome sequencing and panel sequencing): See Table 2, Column 1-"Gene", Column 2-"Alternative names", Column 3-"OMIM# of gene" and Column 4-"Cytogenetic location". Review of the analytical and clinical validity as well as of the clinical utility of DNA-based testing for mutations in the gene(s) in diagnostic, predictive and prenatal settings, and for risk assessment in relatives.

Purpose: To develop a comprehensive next-generation sequencing panel assay that screens genes known to cause developmental eye disorders and inherited eye disease and to evaluate its diagnostic yield in a pediatric cohort with malformations of the globe, anterior segment anomalies, childhood glaucoma, or a combination thereof., Design: Evaluation of diagnostic test., Participants: Two hundred seventy-seven children, 0 to 16 years of age, diagnosed with nonsyndromic or syndromic developmental eye defects without a genetic diagnosis., Methods: We developed a new oculome panel using a custom-designed Agilent SureSelect QXT target capture method (Agilent Technologies, Santa Clara, CA) to capture and perform parallel high-throughput sequencing analysis of 429 genes associated with eye disorders. Bidirectional Sanger sequencing confirmed suspected pathogenic variants., Main Outcome Measures: Collated clinical details and oculome molecular genetic results., Results: The oculome design covers 429 known eye disease genes; these are subdivided into 5 overlapping virtual subpanels for anterior segment developmental anomalies including glaucoma (ASDA; 59 genes), microphthalmia-anophthalmia-coloboma (MAC; 86 genes), congenital cataracts and lens-associated conditions (70 genes), retinal dystrophies (RET; 235 genes), and albinism (15 genes), as well as additional genes implicated in optic atrophy and complex strabismus (10 genes). Panel development and testing included analyzing 277 clinical samples and 3 positive control samples using Illumina sequencing platforms; more than 30× read depth was achieved for 99.5% of the targeted 1.77-Mb region. Bioinformatics analysis performed using a pipeline based on Freebayes and ExomeDepth to identify coding sequence and copy number variants, respectively, resulted in a definitive diagnosis in 68 of 277 samples, with variability in diagnostic yield between phenotypic subgroups: MAC, 8.2% (8 of 98 cases solved); ASDA, 24.8% (28 of 113 cases solved); other or syndromic, 37.5% (3 of 8 cases solved); RET, 42.8% (21 of 49 cases solved); and congenital cataracts and lens-associated conditions, 88.9% (8 of 9 cases solved)., Conclusions: The oculome test diagnoses a comprehensive range of genetic conditions affecting the development of the eye, potentially replacing protracted and costly multidisciplinary assessments and allowing for faster targeted management. The oculome enabled molecular diagnosis of a significant number of cases in our sample cohort of varied ocular birth defects., (Copyright © 2019 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.)

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&#95;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.

Mutations in KCNJ13 are associated with two retinal disorders; Leber congenital amaurosis (LCA) and snowflake vitreoretinal degeneration (SVD). We describe a novel fibrovascular proliferation in the retina of two affected members of a KCNJ13-related LCA family with a homozygous c.458C > T, p.(Thr153Ile) missense mutation. Optical coherence tomography retinal imaging of the kcnj13 mutant zebrafish (obelixtd15 c.502T > C, p.[Phe168Leu]) revealed a late onset retinal degeneration at 12 months, with retinal thinning and associated retinovascular changes, including increased vessel calibre and vitreous deposits. Both human and zebrafish variants are missense and located within the conserved transmembrane M2 protein domain, suggesting that disruption of this region may contribute to retinovascular changes as an additional feature to the previously described LCA phenotype. Close monitoring of other patients with similar mutations may be required to minimise the ensuing retinal damage.