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Background\ud Children with intellectual disability frequently have multiple co-morbid neuropsychiatric conditions and poor physical health. Genomic testing is increasingly recommended as a first-line investigation for these children. We aim to determine the effect of genomics, inheritance, and socioeconomic deprivation on neuropsychiatric risk in children with intellectual disability of genetic origin as compared with the general population.\ud Methods\ud IMAGINE is a prospective cohort study using online mental health and medical assessments in a cohort of 3407 UK participants with intellectual disability and pathogenic genomic variants as identified by the UK's National Health Service (NHS). Our study is on a subset of these participants, including all children aged 4–19 years. We collected diagnostic genomic reports from NHS records and asked primary caregivers to provide an assessment of their child using the Development and Well-Being Assessment (DAWBA), the Strengths and Difficulties Questionnaire (SDQ), the Adaptive Behaviour Assessment System 3 (ABAS-3), and a medical history questionnaire. Each child was assigned a rank based on their postcode using the index of multiple deprivation (IMD). We compared the IMAGINE cohort with the 2017 National Survey of Children's Mental Health in England. The main outcomes of interest were mental health and neurodevelopment according to the DAWBA and SDQ.\ud Findings\ud We recruited 2770 children from the IMAGINE study between Oct 1, 2014 and June 30, 2019, of whom 2397 (86·5%) had a basic assessment of their mental health completed by their families and 1277 (46·1%) completed a medical history questionnaire. The mean age of participants was 9·2 years (SD 3·9); 1339 (55·9%) were boys and 1058 (44·1%) were girls. 355 (27·8%) of 1277 reported a seizure disorder and 814 (63·7%) reported movement or co-ordination problems. 1771 (73·9%) of 2397 participants had a pathogenic copy number variant (CNV) and 626 (26·1%) had a pathogenic single nucleotide variant (SNV). Participants were representative of the socioeconomic spectrum of the UK general population. The relative risk (RR) of co-occurring neuropsychiatric diagnoses, compared with the English national population, was high: autism spectrum disorder RR 29·2 (95% CI 23·9–36·5), ADHD RR 13·5 (95% CI 11·1–16·3). In children with a CNV, those with a familial variant tended to live in more socioeconomically deprived areas than those with a de novo variant. Both inheritance and socioeconomic deprivation contributed to neuropsychiatric risk in those with a CNV.\ud Interpretation\ud Children with genomic variants and intellectual disability are at an increased risk of neuropsychiatric difficulties. CNV variant inheritance and socioeconomic deprivation also contribute to the risk. Early genomic investigations of children with intellectual disability could facilitate the identification of the most vulnerable children. Additionally, harnessing parental expertise using online DAWBA assessments could rapidly identify children with exceptional needs to child mental health services.

Purpose Previous studies suggest that ceramide is a proapoptotic lipid as high levels of ceramides can lead to apoptosis of neuronal cells, including photoreceptors. However, no pathogenic variant in ceramide synthases has been identified in human patients and knockout of various ceramide synthases in mice has not led to photoreceptor degeneration. Methods Exome sequencing was used to identify candidate disease genes in patients with vision loss as confirmed by standard evaluation methods, including electroretinography (ERG) and optical coherence tomography. The vision loss phenotype in mice was evaluated by ERG and histological analyses. Results Here we have identified four patients with cone-rod dystrophy or maculopathy from three families carrying pathogenic variants in TLCD3B. Consistent with the phenotype observed in patients, the Tlcd3bKO/KO mice exhibited a significant reduction of the cone photoreceptor light responses, thinning of the outer nuclear layer, and loss of cone photoreceptors across the retina. Conclusion Our results provide the first link between loss-of-function variants in a ceramide synthase gene and human retinal dystrophy. Establishment of the Tlcd3b knockout murine model, the first in vivo photoreceptor cell degeneration model due to loss of a ceramide synthase, will provide a unique opportunity in probing the role of ceramide in survival and function of photoreceptor cells.

Constrained Coding Regions (CCRs) in the human genome have been derived from DNA sequencing data of large cohorts of healthy control populations, available in the Genome Aggregation Database (gnomAD) [1]. They identify regions depleted of protein-changing variants and thus identify segments of the genome that have been constrained during human evolution. By mapping these DNA-defined regions from genomic coordinates onto the corresponding protein positions and combining this information with protein annotations, we have explored the distribution of CCRs and compared their co-occurrence with different protein functional features, previously annotated at the amino acid level in public databases. As expected, our results reveal that functional amino acids involved in interactions with DNA/RNA, protein-protein contacts and catalytic sites are the protein features most likely to be highly constrained for variation in the control population. More surprisingly, we also found that linear motifs, linear interacting peptides (LIPs), disorder-order transitions upon binding with other protein partners and liquid-liquid phase separating (LLPS) regions are also strongly associated with high constraint for variability. We also compared intra-species constraints in the human CCRs with inter-species conservation and functional residues to explore how such CCRs may contribute to the analysis of protein variants. As has been previously observed, CCRs are only weakly correlated with conservation, suggesting that intraspecies constraints complement interspecies conservation and can provide more information to interpret variant effects.

We describe six persons from three families with three homozygous protein truncating variants in PUS7: c.89_90del (p.Thr30Lysfs(∗)20), c.1348C>T (p.Arg450(∗)), and a deletion of the penultimate exon 15. All these individuals have intellectual disability with speech delay, short stature, microcephaly, and aggressive behavior. PUS7 encodes the RNA-independent pseudouridylate synthase 7. Pseudouridylation is the most abundant post-transcriptional modification in RNA, which is primarily thought to stabilize secondary structures of RNA. We show that the disease-related variants lead to abolishment of PUS7 activity on both tRNA and mRNA substrates. Moreover, pus7 knockout in Drosophila melanogaster results in a number of behavioral defects, including increased activity, disorientation, and aggressiveness supporting that neurological defects are caused by PUS7 variants. Our findings demonstrate that RNA pseudouridylation by PUS7 is essential for proper neuronal development and function.

Mutations in more than 250 genes are implicated in inherited retinal dystrophy; the encoded proteins are involved in a broad spectrum of pathways. The presence of unsolved families after highly parallel sequencing strategies suggests that further genes remain to be identified. Whole-exome and -genome sequencing studies employed here in large cohorts of affected individuals revealed biallelic mutations in ARHGEF18 in three such individuals. ARHGEF18 encodes ARHGEF18, a guanine nucleotide exchange factor that activates RHOA, a small GTPase protein that is a key component of tight junctions and adherens junctions. This biological pathway is known to be important for retinal development and function, as mutation of CRB1, encoding another component, causes retinal dystrophy. The retinal structure in individuals with ARHGEF18 mutations resembled that seen in subjects with CRB1 mutations. Five mutations were found on six alleles in the three individuals: c.808A>G (p.Thr270Ala), c.1617+5G>A (p.Asp540Glyfs ∗ 63), c.1996C>T (p.Arg666 ∗ ), c.2632G>T (p.Glu878 ∗ ), and c.2738_2761del (p.Arg913_Glu920del). Functional tests suggest that each disease genotype might retain some ARHGEF18 activity, such that the phenotype described here is not the consequence of nullizygosity. In particular, the p.Thr270Ala missense variant affects a highly conserved residue in the DBL homology domain, which is required for the interaction and activation of RHOA. Previously, knock-out of Arhgef18 in the medaka fish has been shown to cause larval lethality which is preceded by retinal defects that resemble those seen in zebrafish Crumbs complex knock-outs. The findings described here emphasize the peculiar sensitivity of the retina to perturbations of this pathway, which is highlighted as a target for potential therapeutic strategies.

Background: Each year 95,000 neonates are admitted to intensive care units (ICU) in the UK. With growing evidence that Mendelian diseases present in the neonatal period, there is a need for rapid, systematic, and comprehensive genomic diagnoses in ICUs to assist with acute care decisions and long-term planning within a national health care system. Methods: We performed trio whole genome sequence analysis (WGS) on a prospective cohort of 159 families recruited from neonatal and paediatric intensive care units (NICU and PICU) in the UK over a period of 18 months. We developed a research pipeline in collaboration with the National Health Service (NHS) to deliver validated pertinent pathogenic findings from WGS within 2-3 weeks of recruitment. Findings: 48% of families approached consented to the study and 87% of those recruited provided parental samples for trio analysis. Overall, ~20% received a molecular genetic diagnosis. The phenotypic description of the child was a poor predictor of the gene identified in 87% of cases. The diagnosis affected clinical management in >75% of cases including modification of treatments, initiating new specialist care pathways and/or informing palliative care decisions. A 2-3 week turnaround was sufficient for clinical decision making. Interpretation: The use of WGS in intensively ill children is acceptable to parents and trio analysis facilitates diagnoses. A trio gene agnostic analysis was highly effective in identifying an underlying genetic condition, with phenotypes and symptomatology being primarily used for data interpretation rather than gene selection. Scale up of this process will support NHS commissioning of WGS for first line management of intensively ill children. Funding Statement: The study was supported by the Rosetrees Trust, Cambridge Biomedical Research Centre (FLR and DHR) and the National Institute for Health Research (NIHR) for the NIHR BioResource (grant number RG65966). Declaration of Interests: The authors state: "none declared." Ethics Approval Statement: Participants for this study were recruited through NHS Cambridge University Hospitals Foundation Trust under NRES Cambridge South Research Ethics Committee approval 13/EE/0325.

With a wealth of disease-associated DNA variants being recently reported, the challenges of providing their functional characterization are mounting. Previously, as part of a large systematic resequencing of the X chromosome in 208 unrelated families with nonsyndromic X-linked intellectual disability, we identified three unique variants (two missense and one protein truncating) in USP9X. To assess the functional significance of these variants, we took advantage of the Usp9x knockout mouse we generated. Loss of Usp9x causes reduction in both axonal growth and neuronal cell migration. Although overexpression of wild-type human USP9X rescued these defects, all three USP9X variants failed to rescue axonal growth, caused reduced USP9X protein localization in axonal growth cones, and (in 2/3 variants) failed to rescue neuronal cell migration. Interestingly, in one of these families, the proband was subsequently identified to have a microdeletion encompassing ARID1B, a known ID gene. Given our findings it is plausible that loss of function of both genes contributes to the individual's phenotype. This case highlights the complexity of the interpretations of genetic findings from genome-wide investigations. We also performed proteomics analysis of neurons from both the wild-type and Usp9x knockout embryos and identified disruption of the cytoskeleton as the main underlying consequence of the loss of Usp9x. Detailed clinical assessment of all three families with USP9X variants identified hypotonia and behavioral and morphological defects as common features in addition to ID. Together our data support involvement of all three USP9X variants in ID in these families and provide likely cellular and molecular mechanisms involved. Refereed/Peer-reviewed

We previously reported on nonrecurrent overlapping duplications at Xp11.22 in individuals with nonsyndromic intellectual disability (ID) harboring HSD17B10, HUWE1, and the microRNAs miR-98 and let-7f-2 in the smallest region of overlap. Here, we describe six additional individuals with nonsyndromic ID and overlapping microduplications that segregate in the families. High-resolution mapping of the 12 copy-number gains reduced the minimal duplicated region to the HUWE1 locus only. Consequently, increased mRNA levels were detected for HUWE1, but not HSD17B10. Marker and SNP analysis, together with identification of two de novo events, suggested a paternally derived intrachromosomal duplication event. In four independent families, we report on a polymorphic 70 kb recurrent copy-number gain, which harbors part of HUWE1 (exon 28 to 3' untranslated region), including miR-98 and let-7f-2. Our findings thus demonstrate that HUWE1 is the only remaining dosage-sensitive gene associated with the ID phenotype. Junction and in silico analysis of breakpoint regions demonstrated simple microhomology-mediated rearrangements suggestive of replication-based duplication events. Intriguingly, in a single family, the duplication was generated through nonallelic homologous recombination (NAHR) with the use of HUWE1-flanking imperfect low-copy repeats, which drive this infrequent NAHR event. The recurrent partial HUWE1 copy-number gain was also generated through NAHR, but here, the homologous sequences used were identified as TcMAR-Tigger DNA elements, a template that has not yet been reported for NAHR. In summary, we showed that an increased dosage of HUWE1 causes nonsyndromic ID and demonstrated that the Xp11.22 region is prone to recombination- and replication-based rearrangements.

Copy number variants and indels in 251 families with evidence of X-linked intellectual disability (XLID) were investigated by array comparative genomic hybridization on a high-density oligonucleotide X chromosome array platform. We identified pathogenic copy number variants in 10% of families, with mutations ranging from 2 kb to 11 Mb in size. The challenge of assessing causality was facilitated by prior knowledge of XLID-associated genes and the ability to test for cosegregation of variants with disease through extended pedigrees. Fine-scale analysis of rare variants in XLID families leads us to propose four additional genes, PTCHD1, WDR13, FAAH2, and GSPT2, as candidates for XLID causation and the identification of further deletions and duplications affecting X chromosome genes but without apparent disease consequences. Breakpoints of pathogenic variants were characterized to provide insight into the underlying mutational mechanisms and indicated a predominance of mitotic rather than meiotic events. By effectively bridging the gap between karyotype-level investigations and X chromosome exon resequencing, this study informs discussion of alternative mutational mechanisms, such as noncoding variants and non-X-linked disease, which might explain the shortfall of mutation yield in the well-characterized International Genetics of Learning Disability (IGOLD) cohort, where currently disease remains unexplained in two-thirds of families.

Brown-Vialetto-Van Laere syndrome is a rare neurological disorder with a variable age at onset and clinical course. The key features are progressive ponto-bulbar palsy and bilateral sensorineural deafness. A complex neurological phenotype with a mixed picture of upper and lower motor neuron involvement reminiscent of amyotrophic lateral sclerosis evolves with disease progression. We identified a candidate gene, C20orf54, by studying a consanguineous family with multiple affected individuals and subsequently demonstrated that mutations in this gene were the cause of disease in other, unrelated families.

FG syndrome is a rare X-linked multiple congenital anomaly-cognitive impairment disorder caused by the p.R961W mutation in the MED12 gene. We identified all known patients with this mutation to delineate their clinical phenotype and devise a clinical algorithm to facilitate molecular diagnosis. We ascertained 23 males with the p.R961W mutation in MED12 from 9 previously reported FG syndrome families and 1 new family. Six patients are reviewed in detail. These 23 patients were compared with 48 MED12 mutation-negative patients, who had the clinical diagnosis of FG syndrome. Traits that best discriminated between these two groups were chosen to develop an algorithm with high sensitivity and specificity for the p.R961W MED12 mutation. FG syndrome has a recognizable dysmorphic phenotype with a high incidence of congenital anomalies. A family history of X-linked mental retardation, deceased male infants, and/or multiple fetal losses was documented in all families. The algorithm identifies the p.R961W MED12 mutation-positive group with 100% sensitivity and 90% spec-ificity. The clinical phenotype of FG syndrome defines a recognizable pattern of X-linked multiple congenital anomalies and cognitive impairment. This algorithm can assist the clinician in selecting the patients for testing who are most likely to have the recurrent p.R961W MED12 mutation.

Linkage analysis and DNA sequencing in a family exhibiting an X-linked mental retardation (XLMR) syndrome, characterized by microcephaly, epilepsy, ataxia, and absent speech and resembling Angelman syndrome, identified a deletion in the SLC9A6 gene encoding the Na(+)/H(+) exchanger NHE6. Subsequently, other mutations were found in a male with mental retardation (MR) who had been investigated for Angelman syndrome and in two XLMR families with epilepsy and ataxia, including the family designated as having Christianson syndrome. Therefore, mutations in SLC9A6 cause X-linked mental retardation. Additionally, males with findings suggestive of unexplained Angelman syndrome should be considered as potential candidates for SLC9A6 mutations.

In the course of systematic screening of the X-chromosome coding sequences in 250 families with nonsyndromic X-linked mental retardation (XLMR), two families were identified with truncating mutations in BRWD3, a gene encoding a bromodomain and WD-repeat domain–containing protein. In both families, the mutation segregates with the phenotype in affected males. Affected males have macrocephaly with a prominent forehead, large cupped ears, and mild-to-moderate intellectual disability. No truncating variants were found in 520 control X chromosomes. BRWD3 is therefore a new gene implicated in the etiology of XLMR associated with macrocephaly and may cause disease by altering intracellular signaling pathways affecting cellular proliferation.

Individuals born of consanguineous union have segments of their genomes that are homozygous as a result of inheriting identical ancestral genomic segments through both parents. One consequence of this is an increased incidence of recessive disease within these sibships. Theoretical calculations predict that 6% (1/16) of the genome of a child of first cousins will be homozygous and that the average homozygous segment will be 20 cM in size. We assessed whether these predictions held true in populations that have preferred consanguineous marriage for many generations. We found that in individuals with a recessive disease whose parents were first cousins, on average, 11% of their genomes were homozygous (n = 38; range 5%-20%), with each individual bearing 20 homozygous segments exceeding 3 cM (n = 38; range of number of homozygous segments 7-32), and that the size of the homozygous segment associated with recessive disease was 26 cM (n = 100; range 5-70 cM). These data imply that prolonged parental inbreeding has led to a background level of homozygosity increased approximately 5% over and above that predicted by simple models of consanguinity. This has important clinical and research implications.

Item does not contain fulltext We report the identification of six patients with 3q29 microdeletion syndrome. The clinical phenotype is variable despite an almost identical deletion size. The phenotype includes mild-to-moderate mental retardation, with only slightly dysmorphic facial features that are similar in most patients: a long and narrow face, short philtrum, and high nasal bridge. Autism, gait ataxia, chest-wall deformity, and long and tapering fingers were noted in at least two of six patients. Additional features--including microcephaly, cleft lip and palate, horseshoe kidney and hypospadias, ligamentous laxity, recurrent middle ear infections, and abnormal pigmentation--were observed, but each feature was only found once, in a single patient. The microdeletion is approximately 1.5 Mb in length, with molecular boundaries mapping within the same or adjacent bacterial artificial chromosome (BAC) clones at either end of the deletion in all patients. The deletion encompasses 22 genes, including PAK2 and DLG1, which are autosomal homologues of two known X-linked mental retardation genes, PAK3 and DLG3. The presence of two nearly identical low-copy repeat sequences in BAC clones on each side of the deletion breakpoint suggests that nonallelic homologous recombination is the likely mechanism of disease causation in this syndrome.

We have identified truncating mutations in the human DLG3 (neuroendocrine dlg) gene in 4 of 329 families with moderate to severe X-linked mental retardation. DLG3 encodes synapse-associated protein 102 (SAP102), a member of the membrane-associated guanylate kinase protein family. Neuronal SAP102 is expressed during early brain development and is localized to the postsynaptic density of excitatory synapses. It is composed of three amino-terminal PDZ domains, an src homology domain, and a carboxyl-terminal guanylate kinase domain. The PDZ domains interact directly with the NR2 subunits of the NMDA glutamate receptor and with other proteins responsible for NMDA receptor localization, immobilization, and signaling. The mutations identified in this study all introduce premature stop codons within or before the third PDZ domain, and it is likely that this impairs the ability of SAP102 to interact with the NMDA receptor and/or other proteins involved in downstream NMDA receptor signaling pathways. NMDA receptors have been implicated in the induction of certain forms of synaptic plasticity, such as long-term potentiation and long-term depression, and these changes in synaptic efficacy have been proposed as neural mechanisms underlying memory and learning. The disruption of NMDA receptor targeting or signaling, as a result of the loss of SAP102, may lead to altered synaptic plasticity and may explain the intellectual impairment observed in individuals with DLG3 mutations.

We report the identification and cloning of a novel human gene, CXorf17, together with its mouse ortholog, orf34. The human and mouse transcripts were cloned from brain cDNA and encode deduced proteins of 1096 and 1091 amino acids, respectively. These proteins are 92% identical and 95% similar at the protein level. CXorf17 appears to be expressed at low levels and could be detected by RT-PCR in several adult and fetal human tissues. Analysis of the deduced amino acid sequence identified five putative transmembrane domains but no significant homology to previously described protein domains or sequence motifs. The CXorf17 protein has homology to two other non-annotated human proteins, C9orf10 and BC012177, the sequence similarity between them being strongest across two discrete domains of 250–270 amino acids in the N- and C-terminal parts of their sequences. We propose that these proteins belong to a previously undescribed family of putative transmembrane proteins. The identification of ESTs coding for similar proteins in other chordates but not lower eukaryotes suggests that these proteins may have first evolved during early chordate evolution. CXorf17 consists of 16 coding exons and maps to Xp11.22, approximately 14 kb telomeric to PRKWNK3 and 27 kb centromeric to KIAA1111. Its identification contributes to the annotation of expressed genes in the proximal part of the X chromosome.