Abstract We combined deep phenotype data and whole-genome sequencing results from the UK 100,000 Genomes Project (100KGP) to characterize the genetic spectrum of infantile nystagmus and albinism, and to explore genotype–phenotype correlations in this cohort. Participants were enrolled in the study based on the clinical codes for albinism or infantile nystagmus. Whole genome sequencing data was retrieved and variants in known nystagmus/albinism genes (PanelApp R39 panel) were analysed alongside genome-wide findings. We ascertained 473 affected individuals (388 families). Positive genetic findings were obtained in 218 participants (46%), including 176 (37%) with definitive diagnoses. Pathogenic variants were found in 16 of 38 panel genes, most commonly in TYR (56 families) and OCA2 (21 families). Recurrent variants (24% of 103 different variants) were identified in six genes. An additional 36 off-panel genes accounted for diagnoses in 45 families, including four dual genetic diagnoses in three families. Phenotypically, refractive errors and foveal hypoplasia-related diagnoses were significantly enriched (odds ratio ~2.8 for refractive disorders). Strabismus and neurodevelopmental features were also over-represented in the cohort. We show that whole-genome sequencing provided a high diagnostic yield in infantile nystagmus/albinism and uncovered a broad allelic spectrum. Integrating comprehensive phenotype data identified distinct genotype–phenotype relationships.

PURPOSE:The thousand and one kinase (TAOK) proteins are a group of serine/threonine-protein kinases involved in signaling pathways, cytoskeleton regulation, and neuronal development. TAOK1 variants are associated with a neurodevelopmental disorder (NDD) characterized by distinctive facial features, hypotonia, and feeding difficulties. TAOK2 variants have been reported to be associated with autism and early-onset obesity. However, a distinct TAOK2-NDD has not yet been delineated. METHODS:We retrospectively studied the clinical and genetic data of individuals recruited from several centers with TAOK1 and TAOK2 variants that were detected through exome and genome sequencing. RESULTS:We report 50 individuals with TAOK1 variants with associated phenotypes, including neurodevelopmental abnormalities (100%), macrocephaly (83%), and hypotonia (58%). We report male genital anomalies and hypoglycemia as novel phenotypes. Thirty-seven unique TAOK1 variants were identified. Most of the missense variants clustered in the protein kinase domain at residues that are intolerant to missense variation. We report 10 individuals with TAOK2 variants with associated phenotypes, including neurodevelopmental abnormalities (100%), macrocephaly (75%), autism (75%), and obesity (70%). CONCLUSION:We describe the largest cohort of TAOK1-NDD to date, to our knowledge, expanding its phenotype and genotype spectrum with 30 novel variants. We delineated the phenotype of a novel TAOK2-NDD associated with neurodevelopmental abnormalities, autism, macrocephaly, and obesity.

Genome sequencing is available as a clinical test in the UK through the Genomic Medicine Service (GMS). The GMS analytical strategy predominantly filters genome data on preselected gene panels. Whilst this reduces variants requiring assessment by reporting laboratories, pathogenic variants outside applied panels may be missed, and variants in genes without established disease–gene relationships are largely ignored. This study compares the analysis of a research exome to a GMS clinical genome for the same patients. For the research exome, we applied a panel-agnostic approach filtering for variants with High Pathogenic Potential (HiPPo) using ClinVar, allele frequency, and in silico prediction tools. We then restricted HiPPo variants to Gene Curation Coalition (GenCC) disease genes. These results were compared with the GMS genome panel-based approach. Twenty-four participants from eight families underwent parallel research exome and GMS genome sequencing. Exome HiPPo analysis identified a similar number of variants as the GMS panel-based approach. GMS genome analysis returned two pathogenic variants and one de novo variant. Exome HiPPo analysis returned the same variants plus an additional pathogenic variant and three further de novo variants in novel genes, where case series are underway. When HiPPo was restricted to GenCC disease genes, statistically fewer variants required assessment to identify more pathogenic variants than reported by the GMS, giving a diagnostic rate per variant assessed of 20% for HiPPo versus 3% for the GMS. With UK plans to sequence 5 million genomes, strategies are needed to optimise genome analysis beyond gene panels whilst minimising the burden of variants requiring clinical assessment.

The RhoGEF TRIO is known to play a major role in neuronal development by controlling actin cytoskeleton remodeling, primarily through the activation of the RAC1 GTPase. Numerous de novo mutations in the TRIO gene have been identified in individuals with neurodevelopmental disorders (NDDs). We have previously established the first phenotype/genotype correlation in TRIO-associated diseases, with striking correlation between the clinical features of the individuals and the opposite modulation of RAC1 activity by TRIO variants targeting different domains. The mutations hyperactivating RAC1 are of particular interest, as they are recurrently found in patients and are associated with a severe form of NDD and macrocephaly, indicating their importance in the etiology of the disease. Yet, it remains unknown how these pathogenic TRIO variants disrupt TRIO activity at a molecular level and how they affect neurodevelopmental processes such as axon outgrowth or guidance. Here we report an additional cohort of individuals carrying a pathogenic TRIO variant that reinforces our initial phenotype/genotype correlation. More importantly, by performing conformation predictions coupled to biochemical validation, we propose a model whereby TRIO is inhibited by an intramolecular fold and NDD-associated variants relieve this inhibition, leading to RAC1 hyperactivation. Moreover, we show that in cultured primary neurons and in the zebrafish developmental model, these gain-of-function variants differentially affect axon outgrowth and branching in vitro and in vivo, as compared to loss-of-function TRIO variants. In summary, by combining clinical, molecular, cellular and in vivo data, we provide compelling new evidence for the pathogenicity of novel genetic variants targeting the TRIO gene in NDDs. We report a novel mechanism whereby the fine-tuned regulation of TRIO activity is critical for proper neuronal development and is disrupted by pathogenic mutations.

The TRIO gene encodes a rho guanine exchange factor, the function of which is to exchange GDP to GTP, and hence to activate Rho GTPases, and has been described to impact neurodevelopment. Specific genotype-to-phenotype correlations have been established previously describing striking differentiating features seen in variants located in specific domains of the TRIO gene that are associated with opposite effects on RAC1 activity. Currently, 32 cases with a TRIO gene alteration have been published in the medical literature. Here, we report an additional 25, previously unreported individuals who possess heterozygous TRIO variants and we review the literature. In addition, functional studies were performed on the c.4394A > G (N1465S) and c.6244-2A > G TRIO variants to provide evidence for their pathogenicity. Variants reported by the current study include missense variants, truncating nonsense variants, and an intragenic deletion. Clinical features were previously described and included developmental delay, learning difficulties, microcephaly, macrocephaly, seizures, behavioral issues (aggression, stereotypies), skeletal problems including short, tapering fingers and scoliosis, dental problems (overcrowding/delayed eruption), and variable facial features. Here, we report clinical features that have not been described previously, including specific structural brain malformations such as abnormalities of the corpus callosum and ventriculomegaly, additional psychological and dental issues along with a more recognizable facial gestalt linked to the specific domains of the TRIO gene and the effect of the variant upon the function of the encoded protein. This current study further strengthens the genotype-to-phenotype correlation that was previously established and extends the range of phenotypes to include structural brain abnormalities, additional skeletal, dental, and psychiatric issues.

Missense and truncating variants in the X-chromosome-linked CLCN4 gene, resulting in reduced or complete loss-of-function (LOF) of the encoded chloride/proton exchanger ClC-4, were recently demonstrated to cause a neurocognitive phenotype in both males and females. Through international clinical matchmaking and interrogation of public variant databases we assembled a database of 90 rare CLCN4 missense variants in 90 families: 41 unique and 18 recurrent variants in 49 families. For 43 families, including 22 males and 33 females, we collated detailed clinical and segregation data. To confirm causality of variants and to obtain insight into disease mechanisms, we investigated the effect on electrophysiological properties of 59 of the variants in Xenopus oocytes using extended voltage and pH ranges. Detailed analyses revealed new pathophysiological mechanisms: 25% (15/59) of variants demonstrated LOF, characterized by a "shift" of the voltage-dependent activation to more positive voltages, and nine variants resulted in a toxic gain-of-function, associated with a disrupted gate allowing inward transport at negative voltages. Functional results were not always in line with in silico pathogenicity scores, highlighting the complexity of pathogenicity assessment for accurate genetic counselling. The complex neurocognitive and psychiatric manifestations of this condition, and hitherto under-recognized impacts on growth, gastrointestinal function, and motor control are discussed. Including published cases, we summarize features in 122 individuals from 67 families with CLCN4-related neurodevelopmental condition and suggest future research directions with the aim of improving the integrated care for individuals with this diagnosis.

BACKGROUND:Donnai Barrow Syndrome (DBS) is a rare, multi-system autosomal recessively inherited disorder of relevance to ophthalmologists. To aim to describe the ocular phenotype using multimodal imaging for two cases of genetically confirmed DBS and compare against the published phenotype.MATERIALS AND METHODS:Retrospective case series of two unrelated patients with DBS and review of the literature. Both cases were referred to our tertiary unit for laser prophylaxis against retinal detachment.RESULTS:There was extreme high myopia greater than 20 dioptres without rhegmatogenous retinal detachment (RRD). Anterior segment features included iris transillumination and ciliary body hypoplasia. Posterior segment changes included previously described changes of optic nerve hypoplasia and a strikingly abnormal appearance of the fundus consisting of multiple bilateral giant posterior vortex veins (PVV). The mouse model shows a similar phenotype.CONCLUSIONS:Ectopic vortex veins of the choroid expand the phenotype of DBS and can be helpful in distinguishing the differential diagnosis of high myopia in children. Posterior vortex veins have been described in adult high myopia as acquired but our cases suggest that they could be congenital. Orbital manipulation and hypotony during surgery should be avoided to minimise complications. The evidence to recommend prophylactic laser retinopexy in these cases is inconclusive, and overall we recommend that conservative management should be considered using wide-angle retinal imaging in the clinic.

Use of blood RNA sequencing (RNA-seq) as a splicing analysis tool for clinical interpretation of variants of uncertain significance (VUSs) found via whole-genome and exome sequencing can be difficult for genes that have low expression in the blood due to insufficient read count coverage aligned to specific genes of interest. Here, we present a short amplicon reverse transcription-polymerase chain reaction(RT-PCR) for the detection of genes with low blood expression. Short amplicon RT-PCR, is designed to span three exons where an exon harboring a variant is flanked by one upstream and one downstream exon. We tested short amplicon RT-PCRs for genes that have median transcripts per million (TPM) values less than one according to the genotype-tissue expression database. Median TPM values of genes analyzed in this study are SYN1 = 0.8549, COL1A1 = 0.6275, TCF4 = 0.4009, DSP = .2894, TTN = 0.2851, COL5A2 = 0.1036, TERT = 0.04452, NTRK2 = 0.0344, ABCA4 = 0.00744, PRPH = 0, and WT1 = 0. All these genes show insufficient exon-spanning read coverage in our RNA-seq data to allow splicing analysis. We successfully detected all genes tested except PRPH and WT1. Aberrant splicing was detected in SYN1, TCF4, NTRK2, TTN, and TERT VUSs. Therefore, our results show short amplicon RT-PCR is a useful alternative for the analysis of splicing events in genes with low TPM in blood RNA for clinical diagnostics.

Light activation of the classical light-sensing retinal neurons, the photoreceptors, results in a graded change in membrane potential that ultimately leads to a reduction in neurotransmitter release to the post-synaptic retinal neurons. Photoreceptors show striking powers of adaptation, and for visual processing to function optimally, they must adjust their gain to remain responsive to different levels of ambient light intensity. The presence of a tightly controlled balance of inward and outward currents modulated by several different types of ion channels is what gives photoreceptors their remarkably dynamic operating range. Part of the resetting and modulation of this operating range is controlled by potassium and calcium voltage-gated channels, which are involved in setting the dark resting potential and synapse signal processing, respectively. Their essential contribution to visual processing is further confirmed in patients suffering from cone dystrophy with supernormal rod response (CDSRR) and congenital stationary night blindness type 2 (CSNB2), both conditions that lead to irreversible vision loss. This review will discuss these two types of voltage-gated ion channels present in photoreceptors, focussing on their structure and physiology, and their role in visual processing. It will also discuss the use and benefits of knockout mouse models to further study the function of these channels and what routes to potential treatments could be applied for CDSRR and CSNB2.

BackgroundPrimary ciliary dyskinesia (PCD) is a heterogeneous inherited disorder caused by mutations in approximately 50 cilia-related genes. PCD genotype–phenotype relationships have mostly arisen from small case series because existing statistical approaches to investigating relationships have been unsuitable for rare diseases.MethodsWe applied a topological data analysis (TDA) approach to investigate genotype–phenotype relationships in PCD. Data from separate training and validation cohorts included 396 genetically defined individuals carrying pathogenic variants in PCD genes. To develop the TDA models, 12 clinical and diagnostic variables were included. TDA-driven hypotheses were subsequently tested using traditional statistics.ResultsDisease severity at diagnosis, measured by forced expiratory volume in 1 s (FEV1) z-score, was significantly worse in individuals withCCDC39mutations (compared to other gene mutations) and better in those withDNAH11mutations; the latter also reported less neonatal respiratory distress. Patients without neonatal respiratory distress had better preserved FEV1at diagnosis. Individuals withDNAH5mutations were phenotypically diverse. Cilia ultrastructure and beat pattern defects correlated closely to specific causative gene groups, confirming these tests can be used to support a genetic diagnosis.ConclusionsThis large scale, multi-national study presents PCD as a syndrome with overlapping symptoms and variations in phenotype according to genotype. TDA modelling confirmed genotype–phenotype relationships reported by smaller studies (e.g.FEV1worse withCCDC39mutation) and identified new relationships, including FEV1preservation withDNAH11mutations and diversity of severity withDNAH5mutations.

Purpose : Cone photoreceptors (PR) play a critical role in vision as they are responsible for acuity and colour vision. Their dysfunction is behind vision loss in different types of inherited retinal degeneration (IRD). A complete understanding of the aberrant molecular and cellular processes that arise during these diseases is hampered by the relatively small proportion of cone cells the retina. In this study we have utilised advances in next generation sequencing to perform single cell RNA sequencing (scRNA-seq) on individual cone PR from three different mouse models of IRD to investigate transcriptional differences in cone cell survival and death. Methods : Retinas were collected at postnatal day 24 from two cone dystrophies (Pde6ccpfl1 and Gnat2cpfl5) and one rod-cone dystrophy (Pde6brd1) mouse models of IRD, in which cones were labelled with a green fluorescent reporter (GFP). FACS isolated GFP positive cones were collected in 96-well plates and processed for sequencing using 2×75 paired-end chemistry on an Illumina NextSeq, using a scRNA-seq process adapted from SMARTseq2 and MARS-seq approaches. Results : There were 118 differentially expressed (DE) genes common to all models and these were associated with gene ontology biological processes of histone modification and mitochondrial dysfunction. Interestingly, there were more similarities in expression profiles between the Gnat2cpfl5 and Pde6brd1 (139 DE genes, correlating with mitochondrial dysfunction) than compared to the two cone models (44 DE genes, associated with energy production and oxidation). Pathway analysis of exclusive DE profiles of each model (Gnat2cpfl= 290 genes; Pde6ccpfl1= 417 genes; Pde6brd1= 373 genes) revealed enrichment of pluripotency, mRNA processing and NF-κB signalling pathways within up-regulated genes, in contrast to down-regulated DE genes predominantly associated with the electron transport chain, oxidative phosphorylation and translation factors, respectively. Conclusions : Cone-specific single cell RNA-seq of different IRD models revealed significant transcriptional differences both across different diseases and within each group, and highlighted the cell heterogeneity within cone-specific diseases.

Mutations that cause PCD have been reported in 50 genes. These account for around 70% of cases, with additional genes, and non-coding or synonymous changes in known genes, to be identified. Many adult patients with non-CF bronchiectasis have not been investigated for PCD. UK patients with no genetic confirmation for cause of PCD or bronchiectasis had whole genome testing in the UK 100,000 Genome Project (GP). Ciliopathies accounted for 1% of the rare disease cohort in the 100K GP. There were 143 PCD cases (34 probands) and 163 individuals with non-CF bronchiectasis (93 probands). 31% of PCD patients and 5% of bronchiectasis patients had biallelic pathogenic mutations in known PCD genes. We report on these genetically solved cases. In addition to these solved cases, we have identified 21 PCD patients (17%) and 31 non-CF bronchiectasis patients (22%) who have either one pathogenic variant or two variants of unknown significance (VUS) in relevant disease genes. We hypothesise that in patients with a single pathogenic variant identified, a second intronic or synonymous/non-synonymous deep exonic variant is affecting splicing, or that one or both VUS in patients will affect splicing. Using RNA analysis of ALI-cultured nasal ciliated epithelium, we demonstrate how we can uplift diagnostics in these cases (Figure Time course analysis of PCD gene expression during ALI-culture of respiratory epithelium using RNAseq).

Next generation sequencing has disrupted genetic testing, allowing far more scope in the tests applied. The appropriate sections of the genome to be tested can now be readily selected, from single mutations to whole-genome sequencing. One product offering within this spectrum are focused exomes, targeting ~5,000 genes know to be implicated in human disease. These are designed to offer a flexible platform offering high diagnostic yield with a reduction in sequencing requirement compared to whole exome sequencing. Here, we have undertaken sequencing of control DNA samples and compare two kits, the Illumina TruSight One and the Agilent SureSelect Focused Exome. Characteristics of the kits are comprehensively evaluated. Despite the larger design region of the Agilent kit, we find that the Illumina kit performs better in terms of gene coverage, as well as coverage of clinically relevant loci. We provide exhaustive coverage statistics for each kit to aid the assessment of their suitability and provide read data for control DNA samples to allow for bioinformatic benchmarking by users developing pipelines for these data.

Purpose In Bornholm eye disease, a defect in the splicing of transcripts from a variant OPN1LW opsin gene leads to a depletion in spliced transcript levels and, consequently, a reduction in photopigment in photoreceptors expressing the variant gene. Methods Myopic and age-matched control subjects were drawn from the Western Australian Pregnancy Cohort (Raine) Study and the Norfolk Island Eye Study groups. The OPN1LW opsin gene was amplified using long-range PCR methodology and was fully sequenced. Expression of variant opsins was evaluated using quantitative PCR (qPCR). RNA secondary structure changes arising from identified variants were predicted by modeling. Results Forty-two nucleotide sites were found to vary across the 111 subjects studied. Of these, 15 had not been previously reported, with three present only in myopic individuals. Expression of these variants in transfected human embryonic kidney (HEK293T) cells demonstrated that splicing efficiencies were not affected. However, gene transcripts from two of the three variants were significantly depleted. RNA secondary structure modeling predicted that these single nucleotide changes could affect RNA stability. Conclusions None of the variants identified in myopic individuals appeared to alter the efficiency of transcript splicing. However, two resulted in a significant reduction in the number of spliced and unspliced transcripts, indicating an overall reduction in steady-state transcript stability. Such a change would be expected to result in a reduced amount of photopigment, and this may be a contributing factor in the development of myopia.