NRXN1α+/- is associated with increased excitability in ASD iPSC-derived neurons.

BACKGROUND: NRXN1 deletions are identified as one of major rare risk factors for autism spectrum disorder (ASD) and other neurodevelopmental disorders. ASD has 30% co-morbidity with epilepsy, and the latter is associated with excessive neuronal firing. NRXN1 encodes hundreds of presynaptic neuro-adhesion proteins categorized as NRXN1α/ß/γ. Previous studies on cultured cells show that the short NRXN1ß primarily exerts excitation effect, whereas the long NRXN1α which is more commonly deleted in patients involves in both excitation and inhibition. However, patient-derived models are essential for understanding functional consequences of NRXN1α deletions in human neurons. We recently derived induced pluripotent stem cells (iPSCs) from five controls and three ASD patients carrying NRXN1α+/- and showed increased calcium transients in patient neurons. METHODS: In this study we investigated the electrophysiological properties of iPSC-derived cortical neurons in control and ASD patients carrying NRXN1α+/- using patch clamping. Whole genome RNA sequencing was carried out to further understand the potential underlying molecular mechanism. RESULTS: NRXN1α+/- cortical neurons were shown to display larger sodium currents, higher AP amplitude and accelerated depolarization time. RNASeq analyses revealed transcriptomic changes with significant upregulation glutamatergic synapse and ion channels/transporter activity including voltage-gated potassium channels (GRIN1, GRIN3B, SLC17A6, CACNG3, CACNA1A, SHANK1), which are likely to couple with the increased excitability in NRXN1α+/- cortical neurons. CONCLUSIONS: Together with recent evidence of increased calcium transients, our results showed that human NRXN1α+/- isoform deletions altered neuronal excitability and non-synaptic function, and NRXN1α+/- patient iPSCs may be used as an ASD model for therapeutic development with calcium transients and excitability as readouts.

Catalogue of inherited disorders found among the Irish Traveller population.

Background Irish Travellers are an endogamous, nomadic, ethnic minority population mostly resident on the island of Ireland with smaller populations in Europe and the USA. High levels of consanguinity result in many rare autosomal recessive disorders. Due to founder effects and endogamy, most recessive disorders are caused by specific homozygous mutations unique to this population. Key clinicians and scientists with experience in managing rare disorders seen in this population have developed a de facto advisory service on differential diagnoses to consider when faced with specific clinical scenarios. Objective(s) To catalogue all known inherited disorders found in the Irish Traveller population. Methods We performed detailed literature and database searches to identify relevant publications and the disease mutations of known genetic disorders found in Irish Travellers. Results We identified 104 genetic disorders: 90 inherited in an autosomal recessive manner; 13 autosomal dominant and one a recurring chromosomal duplication. Conclusion We have collated our experience of inherited disorders found in the Irish Traveller population to make it publically available through this publication to facilitate a targeted genetic approach to diagnostics in this ethnic group.

Recessive NEK9 mutation causes a lethal skeletal dysplasia with evidence of cell cycle and ciliary defects.

Skeletal dysplasias are a clinically and genetically heterogeneous group of bone and cartilage disorders. Whilst >450 skeletal dysplasias have been reported, 30% are genetically uncharacterized. We report two Irish Traveller families with a previously undescribed lethal skeletal dysplasia characterized by fetal akinesia, shortening of all long bones, multiple contractures, rib anomalies, thoracic dysplasia, pulmonary hypoplasia and protruding abdomen. Single nucleotide polymorphism homozygosity mapping and whole exome sequencing identified a novel homozygous stop-gain mutation in NEK9 (c.1489C>T; p.Arg497*) as the cause of this disorder. NEK9 encodes a never in mitosis gene A-related kinase involved in regulating spindle organization, chromosome alignment, cytokinesis and cell cycle progression. This is the first disorder to be associated with NEK9 in humans. Analysis of NEK9 protein expression and localization in patient fibroblasts showed complete loss of full-length NEK9 (107 kDa). Functional characterization of patient fibroblasts showed a significant reduction in cell proliferation and a delay in cell cycle progression. We also provide evidence to support possible ciliary associations for NEK9. Firstly, patient fibroblasts displayed a significant reduction in cilia number and length. Secondly, we show that the NEK9 orthologue in Caenorhabditis elegans, nekl-1, is almost exclusively expressed in a subset of ciliated cells, a strong indicator of cilia-related functions. In summary, we report the clinical and molecular characterization of a lethal skeletal dysplasia caused by NEK9 mutation and suggest that this disorder may represent a novel ciliopathy.

An inherited duplication at the gene p21 Protein-Activated Kinase 7 (PAK7) is a risk factor for psychosis.

Identifying rare, highly penetrant risk mutations may be an important step in dissecting the molecular etiology of schizophrenia. We conducted a gene-based analysis of large (>100 kb), rare copy-number variants (CNVs) in the Wellcome Trust Case Control Consortium 2 (WTCCC2) schizophrenia sample of 1564 cases and 1748 controls all from Ireland, and further extended the analysis to include an additional 5196 UK controls. We found association with duplications at chr20p12.2 (P = 0.007) and evidence of replication in large independent European schizophrenia (P = 0.052) and UK bipolar disorder case-control cohorts (P = 0.047). A combined analysis of Irish/UK subjects including additional psychosis cases (schizophrenia and bipolar disorder) identified 22 carriers in 11 707 cases and 10 carriers in 21 204 controls [meta-analysis Cochran-Mantel-Haenszel P-value = 2 × 10(-4); odds ratio (OR) = 11.3, 95% CI = 3.7, ∞]. Nineteen of the 22 cases and 8 of the 10 controls carried duplications starting at 9.68 Mb with similar breakpoints across samples. By haplotype analysis and sequencing, we identified a tandem ~149 kb duplication overlapping the gene p21 Protein-Activated Kinase 7 (PAK7, also called PAK5) which was in linkage disequilibrium with local haplotypes (P = 2.5 × 10(-21)), indicative of a single ancestral duplication event. We confirmed the breakpoints in 8/8 carriers tested and found co-segregation of the duplication with illness in two additional family members of one of the affected probands. We demonstrate that PAK7 is developmentally co-expressed with another known psychosis risk gene (DISC1) suggesting a potential molecular mechanism involving aberrant synapse development and plasticity.

Novel European SLC1A4 variant: infantile spasms and population ancestry analysis.

SLC1A4 deficiency is a recently described neurodevelopmental disorder associated with microcephaly, global developmental delay, abnormal myelination, thin corpus callosum and seizures. It has been mainly reported in the Ashkenazi-Jewish population with affected individuals homozygous for the p.Glu256Lys variant. Exome sequencing performed in an Irish proband identified a novel homozygous nonsense SLC1A4 variant [p.Trp453*], confirming a second case of SLC1A4-associated infantile spasms. As this is the first European identified, population ancestry analysis of the Exome Aggregation Consortium database was performed to determine the wider ethnic background of SLC1A4 deficiency carriers. p.Glu256Lys was found in Hispanic and South Asian populations. Other potential disease-causing variants were also identified. Investigation for SLC1A4 deficiency should be performed regardless of ethnicity and extend to include unexplained early-onset epileptic encephalopathy.

Unexplained early onset epileptic encephalopathy: Exome screening and phenotype expansion.

Early onset epileptic encephalopathies (EOEEs) represent a significant diagnostic challenge. Newer genomic approaches have begun to elucidate an increasing number of responsible single genes as well as emerging diagnostic strategies. In this single-center study, we aimed to investigate a cohort of children with unexplained EOEE. We performed whole-exome sequencing (WES), targeting a list of 137 epilepsy-associated genes on 50 children with unexplained EOEE. We characterized all phenotypes in detail and classified children according to known electroclinical syndromes where possible. Infants with previous genetic diagnoses, causative brain malformations, or inborn errors of metabolism were excluded. We identified disease-causing variants in 11 children (22%) in the following genes: STXBP1 (n = 3), KCNB1 (n = 2), KCNT1, SCN1A, SCN2A, GRIN2A, DNM1, and KCNA2. We also identified two further variants (in GRIA3 and CPA6) in two children requiring further investigation. Eleven variants were de novo, and in one paternal testing was not possible. Phenotypes were broadened for some variants identified. This study demonstrates that WES is a clinically useful screening tool for previously investigated unexplained EOEE and allows for reanalysis of data as new genes are being discovered. Detailed phenotyping allows for expansion of specific gene disorders leading to epileptic encephalopathy and emerging sub-phenotypes.

Intra-familial variability associated with recessive RYR1 mutation diagnosed prenatally by exome sequencing.

OBJECTIVE: To determine the underlying molecular aetiology in a non-consanguineous Irish family who have had three fetal losses because of a primary myopathy characterised by fetal akinesia, arthrogryposis multiplex, bilateral pulmonary hypoplasia and reduced muscle bulk. METHODS: Fetal DNA extracted from amniotic cells was whole genome amplified and subjected to whole exome sequencing. RESULTS: Whole exome sequencing identified compound heterozygous variants in RYR1 as the cause of the lethal myopathy in this family. All three fetuses were compound heterozygous for a paternally inherited missense variant (c.2113G > A; p.Gly705Arg) and a novel maternally inherited truncating frameshift deletion (c.8843delC; p.Ser2948Cysfs*58). This family did not have the classic cores and fibre type disproportion typically associated with RYR1 mutation. The RYR1 exome finding was made during the couple's third pregnancy and enabled prenatal genetic testing to be undertaken. CONCLUSION: We show that recessive RYR1 mutations can be associated with significant intra-familial variability in clinical presentation which can complicate prediction of clinical outcome. RYR1 mutations can also cause diverse muscle pathologies which thwarts diagnosis. This study demonstrates the impact that exome-based diagnoses can have for families with lethal disorders. © 2016 John Wiley & Sons, Ltd.

A case report of primary ciliary dyskinesia, laterality defects and developmental delay caused by the co-existence of a single gene and chromosome disorder.

BACKGROUND: Primary ciliary dyskinesia (PCD) is a rare autosomal recessive disorder characterised by abnormal ciliary motion and impaired mucociliary clearance, leading to recurrent respiratory infections, sinusitis, otitis media and male infertility. Some patients also have laterality defects. We recently reported the identification of three disease-causing PCD genes in the Irish Traveller population; RSPH4A, DYX1C1 and CCNO. We have since assessed an additional Irish Traveller family with a complex phenotype involving PCD who did not have any of the previously identified PCD mutations. CASE PRESENTATION: In this study we report on a family with three children with PCD and various laterality defects. In addition, one child (V:1) has mild-to-moderate developmental delay and one child has speech delay (V:2). Developmental delay is not usually associated with PCD and is likely to be caused by an additional genetic abnormality. Transmission electron microscopy showed variable inner and outer dynein arm defects. Exome sequencing identified a homozygous missense variant in CCDC103 (c.461A > C; p.His154Pro) as the most likely cause of the PCD and laterality defects in this family. However, as mutation in CCDC103 would not account for the developmental delay, array comparative genomic hybridisation was undertaken and identified a maternally inherited gain of ~1.6 Mb (chr17:34,611,352-36,248,918). Gains at this locus are associated with 17q12 duplication syndrome which includes speech and language delay. CONCLUSION: We report on a variable and complex phenotype caused by the co-inheritance of a single gene mutation in CCDC103 and a microduplication at 17q12, both on chromosome 17. The co-existence of a single gene and chromosome disorder is unusual but accounts for the spectrum of clinical features in this family. In addition, our study brings the total number of PCD genes in the Irish Traveller population to four and we suspect additional PCD genes are yet to be identified. Although, on a global scale, PCD is associated with extensive genetic heterogeneity, finding such a high number of causative PCD genes within the relatively small Irish Traveller population was unexpected.

ANG mutations segregate with familial and 'sporadic' amyotrophic lateral sclerosis.

We recently identified angiogenin (ANG) as a candidate susceptibility gene for amyotrophic lateral sclerosis (ALS), a neurodegenerative disorder characterized by adult-onset loss of motor neurons. We now report the finding of seven missense mutations in 15 individuals, of whom four had familial ALS and 11 apparently 'sporadic' ALS. Our findings provide further evidence that variations in hypoxia-inducible genes have an important role in motor neuron degeneration.

Towards the identification of a genetic basis for Landau-Kleffner syndrome.

OBJECTIVE: To establish the genetic basis of Landau-Kleffner syndrome (LKS) in a cohort of two discordant monozygotic (MZ) twin pairs and 11 isolated cases. METHODS: We used a multifaceted approach to identify genetic risk factors for LKS. Array comparative genomic hybridization (CGH) was performed using the Agilent 180K array. Whole genome methylation profiling was undertaken in the two discordant twin pairs, three isolated LKS cases, and 12 control samples using the Illumina 27K array. Exome sequencing was undertaken in 13 patients with LKS including two sets of discordant MZ twins. Data were analyzed with respect to novel and rare variants, overlapping genes, variants in reported epilepsy genes, and pathway enrichment. RESULTS: A variant (cG1553A) was found in a single patient in the GRIN2A gene, causing an arginine to histidine change at site 518, a predicted glutamate binding site. Following copy number variation (CNV), methylation, and exome sequencing analysis, no single candidate gene was identified to cause LKS in the remaining cohort. However, a number of interesting additional candidate variants were identified including variants in RELN, BSN, EPHB2, and NID2. SIGNIFICANCE: A single mutation was identified in the GRIN2A gene. This study has identified a number of additional candidate genes including RELN, BSN, EPHB2, and NID2. A PowerPoint slide summarizing this article is available for download in the Supporting Information section here.

A genome-wide association study of recipient genotype and medium-term kidney allograft function.

BACKGROUND: We examined, through genome-wide association studies (GWAS), the correlation between recipient genetic variation and renal function at five yr. METHODS: Our cohort contained 326 Irish, first time, kidney-only, deceased donor, transplant recipients on calcineurin inhibitors (263 had a functioning graft at five yr) between 1993 and 2002. Outcomes were creatinine at five yr and long-term graft function. RESULTS: Two variants were identified showing borderline genome-wide significance - one on chromosome 18 (p = 4.048e-08, rs6565887) and another on chromosome 14 (p = 7.631e-08, rs3811321). Individually, the two SNPs explained up to 8.8% and 11.29% of five-yr creatinine variance, respectively, while together they explained up to 17.4% of trait variance. Both variants were predictors of long-term allograft function (p = 0.004, 70% vs 30% survival at 10 yr). The chromosome 14 variant is located in the intergenic region of the T-Cell Receptor Alpha locus. CONCLUSIONS: Using a genome-wide approach, we have identified two associations with five-yr creatinine levels in renal transplant recipients treated with calcineurin inhibitors. Independent replication is now warranted to clarify the clinical significance of these results.

Recessive mutations in MCM4/PRKDC cause a novel syndrome involving a primary immunodeficiency and a disorder of DNA repair.

BACKGROUND: A study is presented of 10 children with a novel syndrome born to consanguineous parents from the Irish Traveller population. The syndrome is characterised by a natural killer (NK) cell deficiency, evidence of an atypical Fanconi's type DNA breakage disorder, and features of familial glucocorticoid deficiency (FGD). The NK cell deficiency probably accounts for the patients' recurrent viral illnesses. Molecular tests support a diagnosis of mosaic Fanconi's anaemia, but the patients do not present with any of the expected clinical features of the disorder. The symptomatic presentation of FGD was delayed in onset and may be a secondary phenotype. As all three phenotypes segregate together, the authors postulated that the NK cell deficiency, DNA repair disorder and FGD were caused by a single recessive genetic event. METHODS: Single-nucleotide polymorphism homozygosity mapping and targeted next-generation sequencing of 10 patients and 16 unaffected relatives. RESULTS: A locus for the syndrome was identified at 8p11.21-q11.22. Targeted resequencing of the candidate region revealed a homozygous mutation in MCM4/PRKDC in all 10 affected individuals. Consistent with the observed DNA breakage disorder, MCM4 and PRKDC are both involved in the ATM/ATR (ataxia-telangiectasia-mutated/ATM-Rad 3-related) DNA repair pathway, which is defective in patients with Fanconi's anaemia. Deficiency of PRKDC in mice has been shown to result in an abnormal NK cell physiology similar to that observed in these patients. CONCLUSION: Mutations in MCM4/PRKDC represent a novel cause of DNA breakage and NK cell deficiency. These findings suggest that clinicians should consider this disorder in patients with failure to thrive who develop pigmentation or who have recurrent infections.

Identification of a mutation in LARS as a novel cause of infantile hepatopathy.

Infantile hepatopathies are life-threatening liver disorders that manifest in the first few months of life. We report on a consanguineous Irish Traveller family that includes six individuals presenting with acute liver failure in the first few months of life. Additional symptoms include anaemia, renal tubulopathy, developmental delay, seizures, failure to thrive and deterioration of liver function with minor illness. The multisystem manifestations suggested a possible mitochondrial basis to the disorder. However, known causes of childhood liver failure and mitochondrial disease were excluded in this family by biochemical, metabolic and genetic analyses. We aimed to identify the underlying risk gene using homozygosity mapping and whole exome sequencing. SNP homozygosity mapping identified a candidate locus at 5q31.3-q33.1. Whole exome sequencing identified 1 novel homozygous missense mutation within the 5q31.3-q33.1 candidate region that segregated with the hepatopathy. The candidate mutation is located in the LARS gene which encodes a cytoplasmic leucyl-tRNA synthetase enzyme responsible for exclusively attaching leucine to its cognate tRNA during protein translation. Knock-down of LARS in HEK293 cells did not impact on mitochondrial function even when the cells were put under physiological stress. The molecular studies confirm the findings of the patients' biochemical and genetic analyses which show that the hepatopathy is not a mitochondrial-based dysfunction problem, despite clinical appearances. This study highlights the clinical utility of homozygosity mapping and exome sequencing in diagnosing recessive liver disorders. It reports mutation of a cytoplasmic aminoacyl-tRNA synthetase enzyme as a possible novel cause of infantile hepatopathy and underscores the need to consider mutations in LARS in patients with liver disease and multisystem presentations.

First implication of STRA6 mutations in isolated anophthalmia, microphthalmia, and coloboma: a new dimension to the STRA6 phenotype.

Microphthalmia, anophthalmia, and coloboma (MAC) are structural congenital eye malformations that cause a significant proportion of childhood visual impairments. Several disease genes have been identified but do not account for all MAC cases, suggesting that additional risk loci exist. We used single nucleotide polymorphism (SNP) homozygosity mapping (HM) and targeted next-generation sequencing to identify the causative mutation for autosomal recessive isolated colobomatous microanophthalmia (MCOPCB) in a consanguineous Irish Traveller family. We identified a double-nucleotide polymorphism (g.1157G>A and g.1156G>A; p.G304K) in STRA6 that was homozygous in all of the MCOPCB patients. The STRA6 p.G304K mutation was subsequently detected in additional MCOPCB patients, including one individual with Matthew-Wood syndrome (MWS; MCOPS9). STRA6 encodes a transmembrane receptor involved in vitamin A uptake, a process essential to eye development and growth. We have shown that the G304K mutant STRA6 protein is mislocalized and has severely reduced vitamin A uptake activity. Furthermore, we reproduced the MCOPCB phenotype in a zebrafish disease model by inhibiting retinoic acid (RA) synthesis, suggesting that diminished RA levels account for the eye malformations in STRA6 p.G304K patients. The current study demonstrates that STRA6 mutations can cause isolated eye malformations in addition to the congenital anomalies observed in MWS.

Rapid and Laboratory SARS-CoV-2 Antibody Testing in High-Risk Hospital Associated Cohorts of Unknown COVID-19 Exposure, a Validation and Epidemiological Study After the First Wave of the Pandemic.

Objective: We aimed to use SARS-CoV-2 antibody tests to assess the asymptomatic seroprevalence of individuals in high-risk hospital cohorts who's previous COVID-19 exposure is unknown; staff, and patients requiring haemodialysis or chemotherapy after the first wave. Methods: In a single Center, study participants had five SARS-CoV-2 antibody tests done simultaneously; one rapid diagnostic test (RDT) (Superbio Colloidal Gold IgM/IgG), and four laboratory tests (Roche Elecsys® Anti-SARS-CoV-2 IgG [RE], Abbott Architect i2000SR IgG [AAr], Abbott Alinity IgG [AAl], and Abbott Architect IgM CMIA). To determine seroprevalence, only positive test results on laboratory assay were considered true positives. Results: There were 157 participants, of whom 103 (65.6%) were female with a median age of 50 years (range 19-90). The IgG component of the RDT showed a high number of false positives (n = 18), was inferior to the laboratory assays (p < 0.001 RDT vs. AAl/AAr, p < 0.001 RDT vs. RE), and had reduced specificity (85.5% vs. AAl/AAr, 87.2% vs. RE). Sero-concordance was 97.5% between IgG laboratory assays (RE vs. AAl/AAr). Specificity of the IgM component of the RDT compared to Abbott IgM CMIA was 95.4%. Ten participants had positivity in at least one laboratory assay, seven (9.9%) of which were seen in HCWs. Two (4.1%) hematology/oncology (H/O) patients and a single (2.7%) haemodialysis (HD) were asymptomatically seropositive. Asymptomatic seroprevalence of HCWs compared to patients was not significant (p = 0.105). Conclusion: HCWs (9.9%) had higher, although non-significant asymptomatic seroprevalence of SARS-CoV-2 antibodies compared to high-risk patients (H/O 4.1%, HD 2.7%). An IgM/IgG rapid diagnostic test was inferior to laboratory assays. Sero-concordance of 97.5% was found between IgG laboratory assays, RE vs. AAl/AAr.

Rare Disease Research Partnership (RAinDRoP): a collaborative approach to identify research priorities for rare diseases in Ireland.

Background: The Rare Disease Research Partnership (RAinDRoP) was established in 2018 to bring together a wide variety of diverse voices in the rare disease community in Ireland and form a research partnership. This approach enabled clinicians, patients, carers and researchers to work together to identify top research priorities for rare diseases, which focused on a life-course perspective rather than a disease-specific need.                                                                                                           Methods: A participatory multiple phase approach was used to identify research priorities for rare diseases. The research process involved three main phases: Phase I, Public Consultation Survey on Research in Rare Diseases in Ireland (PCSRRDI); Phase II, Research Prioritisation Workshop (RPW); Phase III, Follow-up Public Consultation and Prioritisation Survey (FWPCPS). Results: In total, 240 individuals completed the phase I PCSRRDI, which comprised of a cross-section of health care professionals, researchers and people living with rare diseases. One thousand and fifteen statements were collected, reflecting issues and shared challenges in rare diseases. A shortlisting step by step was used to identify any statements that had received a total score of above 50% into 10-12 researchable questions or statements per the theme for the phase II workshop. Phase II was focused on three main themes: (1) Route to Diagnosis, (2) Living with Rare Disease, (3) Integrated and Palliative Care. In total, 62 individuals attended the overall workshop; 42 participated in the prioritisation sessions. A cross-section of health care professionals, researchers and people living with rare diseases were engaged at each workshop. Seventy-five individuals completed the final phase III public ranking by priority responses, and they ranked the top 15 research priorities defined by the multi-stakeholders at the phase II consensus meeting. Conclusions: This study identified priorities for rare diseases research aimed at improving the health and wellbeing of people living with rare diseases.

The role of rare compound heterozygous events in autism spectrum disorder.

The identification of genetic variants underlying autism spectrum disorders (ASDs) may contribute to a better understanding of their underlying biology. To examine the possible role of a specific type of compound heterozygosity in ASD, namely, the occurrence of a deletion together with a functional nucleotide variant on the remaining allele, we sequenced 550 genes in 149 individuals with ASD and their deletion-transmitting parents. This approach allowed us to identify additional sequence variants occurring in the remaining allele of the deletion. Our main goal was to compare the rate of sequence variants in remaining alleles of deleted regions between probands and the deletion-transmitting parents. We also examined the predicted functional effect of the identified variants using Combined Annotation-Dependent Depletion (CADD) scores. The single nucleotide variant-deletion co-occurrence was observed in 13.4% of probands, compared with 8.1% of parents. The cumulative burden of sequence variants (n = 68) in pooled proband sequences was higher than the burden in pooled sequences from the deletion-transmitting parents (n = 41, X2 = 6.69, p = 0.0097). After filtering for those variants predicted to be most deleterious, we observed 21 of such variants in probands versus 8 in their deletion-transmitting parents (X2 = 5.82, p = 0.016). Finally, cumulative CADD scores conferred by these variants were significantly higher in probands than in deletion-transmitting parents (burden test, ß = 0.13; p = 1.0 × 10-5). Our findings suggest that the compound heterozygosity described in the current study may be one of several mechanisms explaining variable penetrance of CNVs with known pathogenicity for ASD.