A neurodevelopmental disorder associated with a loss-of-function missense mutation in RAB35.

Rab35 (Ras-associated binding protein) is a small GTPase that regulates endosomal membrane trafficking and functions in cell polarity, cytokinesis, and growth factor signaling. Altered Rab35 function contributes to progression of glioblastoma, defects in primary cilia formation, and altered cytokinesis. Here, we report a pediatric patient with global developmental delay, hydrocephalus, a Dandy-Walker malformation, axial hypotonia with peripheral hypertonia, visual problems, and conductive hearing impairment. Exome sequencing identified a homozygous missense variant in the GTPase fold of RAB35 (c.80G>A; p.R27H) as the most likely candidate. Functional analysis of the R27H-Rab35 variant protein revealed enhanced interaction with its guanine-nucleotide exchange factor, DENND1A and decreased interaction with a known effector, MICAL1, indicating that the protein is in an inactive conformation. Cellular expression of the variant drives the activation of Arf6, a small GTPase under negative regulatory control of Rab35. Importantly, variant expression leads to delayed cytokinesis and altered length, number, and Arl13b composition of primary cilia, known factors in neurodevelopmental disease. Our findings provide evidence of altered Rab35 function as a causative factor of a neurodevelopmental disorder.

USP27X variants underlying X-linked intellectual disability disrupt protein function via distinct mechanisms.

Neurodevelopmental disorders with intellectual disability (ND/ID) are a heterogeneous group of diseases driving lifelong deficits in cognition and behavior with no definitive cure. X-linked intellectual disability disorder 105 (XLID105, #300984; OMIM) is a ND/ID driven by hemizygous variants in the USP27X gene encoding a protein deubiquitylase with a role in cell proliferation and neural development. Currently, only four genetically diagnosed individuals from two unrelated families have been described with limited clinical data. Furthermore, the mechanisms underlying the disorder are unknown. Here, we report 10 new XLID105 individuals from nine families and determine the impact of gene variants on USP27X protein function. Using a combination of clinical genetics, bioinformatics, biochemical, and cell biology approaches, we determined that XLID105 variants alter USP27X protein biology via distinct mechanisms including changes in developmentally relevant protein-protein interactions and deubiquitylating activity. Our data better define the phenotypic spectrum of XLID105 and suggest that XLID105 is driven by USP27X functional disruption. Understanding the pathogenic mechanisms of XLID105 variants will provide molecular insight into USP27X biology and may create the potential for therapy development.

Bi-allelic loss-of-function variants in WBP4, encoding a spliceosome protein, result in a variable neurodevelopmental syndrome.

Over two dozen spliceosome proteins are involved in human diseases, also referred to as spliceosomopathies. WW domain-binding protein 4 (WBP4) is part of the early spliceosomal complex and has not been previously associated with human pathologies in the Online Mendelian Inheritance in Man (OMIM) database. Through GeneMatcher, we identified ten individuals from eight families with a severe neurodevelopmental syndrome featuring variable manifestations. Clinical manifestations included hypotonia, global developmental delay, severe intellectual disability, brain abnormalities, musculoskeletal, and gastrointestinal abnormalities. Genetic analysis revealed five different homozygous loss-of-function variants in WBP4. Immunoblotting on fibroblasts from two affected individuals with different genetic variants demonstrated a complete loss of protein, and RNA sequencing analysis uncovered shared abnormal splicing patterns, including in genes associated with abnormalities of the nervous system, potentially underlying the phenotypes of the probands. We conclude that bi-allelic variants in WBP4 cause a developmental disorder with variable presentations, adding to the growing list of human spliceosomopathies.

SLC4A10 mutation causes a neurological disorder associated with impaired GABAergic transmission.

SLC4A10 is a plasma-membrane bound transporter that utilizes the Na+ gradient to drive cellular HCO3- uptake, thus mediating acid extrusion. In the mammalian brain, SLC4A10 is expressed in principal neurons and interneurons, as well as in epithelial cells of the choroid plexus, the organ regulating the production of CSF. Using next generation sequencing on samples from five unrelated families encompassing nine affected individuals, we show that biallelic SLC4A10 loss-of-function variants cause a clinically recognizable neurodevelopmental disorder in humans. The cardinal clinical features of the condition include hypotonia in infancy, delayed psychomotor development across all domains and intellectual impairment. Affected individuals commonly display traits associated with autistic spectrum disorder including anxiety, hyperactivity and stereotyped movements. In two cases isolated episodes of seizures were reported in the first few years of life, and a further affected child displayed bitemporal epileptogenic discharges on EEG without overt clinical seizures. While occipitofrontal circumference was reported to be normal at birth, progressive postnatal microcephaly evolved in 7 out of 10 affected individuals. Neuroradiological features included a relative preservation of brain volume compared to occipitofrontal circumference, characteristic narrow sometimes 'slit-like' lateral ventricles and corpus callosum abnormalities. Slc4a10 -/- mice, deficient for SLC4A10, also display small lateral brain ventricles and mild behavioural abnormalities including delayed habituation and alterations in the two-object novel object recognition task. Collapsed brain ventricles in both Slc4a10-/- mice and affected individuals suggest an important role of SLC4A10 in the production of the CSF. However, it is notable that despite diverse roles of the CSF in the developing and adult brain, the cortex of Slc4a10-/- mice appears grossly intact. Co-staining with synaptic markers revealed that in neurons, SLC4A10 localizes to inhibitory, but not excitatory, presynapses. These findings are supported by our functional studies, which show the release of the inhibitory neurotransmitter GABA is compromised in Slc4a10-/- mice, while the release of the excitatory neurotransmitter glutamate is preserved. Manipulation of intracellular pH partially rescues GABA release. Together our studies define a novel neurodevelopmental disorder associated with biallelic pathogenic variants in SLC4A10 and highlight the importance of further analyses of the consequences of SLC4A10 loss-of-function for brain development, synaptic transmission and network properties.

Loss-of-function variants in DNM1 cause a specific form of developmental and epileptic encephalopathy only in biallelic state.

BACKGROUND: Developmental and epileptic encephalopathies (DEEs) represent a group of severe neurological disorders characterised by an onset of refractory seizures during infancy or early childhood accompanied by psychomotor developmental delay or regression. DEEs are genetically heterogeneous with, to date, more than 80 different genetic subtypes including DEE31 caused by heterozygous missense variants in DNM1. METHODS: We performed a detailed clinical characterisation of two unrelated patients with DEE and used whole-exome sequencing to identify causative variants in these individuals. The identified variants were tested for cosegregation in the respective families. RESULTS: We excluded pathogenic variants in known, DEE-associated genes. We identified homozygous nonsense variants, c.97C>T; p.(Gln33*) in family 1 and c.850C>T; p.(Gln284*) in family 2, in the DNM1 gene, indicating that biallelic, loss-of-function pathogenic variants in DNM1 cause DEE. CONCLUSION: Our finding that homozygous, loss-of-function variants in DNM1 cause DEE expands the spectrum of pathogenic variants in DNM1. All parents who were heterozygous carriers of the identified loss-of-function variants were healthy and did not show any clinical symptoms, indicating that the type of mutation in DNM1 determines the pattern of inheritance.

Infantile SOD1 deficiency syndrome caused by a homozygous SOD1 variant with absence of enzyme activity.

Pathogenic variants in SOD1, encoding superoxide dismutase 1, are responsible for about 20% of all familial amyotrophic lateral sclerosis cases, through a gain-of-function mechanism. Recently, two reports showed that a specific homozygous SOD1 loss-of-function variant is associated with an infantile progressive motor-neurological syndrome. Exome sequencing followed by molecular studies, including cDNA analysis, SOD1 protein levels and enzymatic activity, and plasma neurofilament light chain levels, were undertaken in an infant with severe global developmental delay, axial hypotonia and limb spasticity. We identified a homozygous 3-bp in-frame deletion in SOD1. cDNA analysis predicted the loss of a single valine residue from a tandem pair (p.Val119/Val120) in the wild-type protein, yet expression levels and splicing were preserved. Analysis of SOD1 activity and protein levels in erythrocyte lysates showed essentially no enzymatic activity and undetectable SOD1 protein in the child, whereas the parents had ∼50% protein expression and activity relative to controls. Neurofilament light chain levels in plasma were elevated, implying ongoing axonal injury and neurodegeneration. Thus, we provide confirmatory evidence of a second biallelic variant in an infant with a severe neurological syndrome and suggest that the in-frame deletion causes instability and subsequent degeneration of SOD1. We highlight the importance of the valine residues at positions V119-120, and suggest possible implications for future therapeutics research.

Homozygous frameshift variant in NTNG2, encoding a synaptic cell adhesion molecule, in individuals with developmental delay, hypotonia, and autistic features.

Regulation of neuronal connectivity and synaptic communication are key to proper functioning of the brain. The Netrin-G subfamily and their cognate receptors are vertebrate-specific synaptic cell adhesion molecules with a role in synapse establishment and function, which seem to have co-evolved to contribute to higher brain functions. We identified a homozygous frameshift variant in NTNG2 (NM_032536.3: c.376dup), encoding Netrin-G2, in eight individuals from four families with global developmental delay, hypotonia, secondary microcephaly, and autistic features. Comparison of haplotypes established this as a founder variant. Previous studies showed that Ntng2-knockout mice have impaired visual, auditory, and motor coordination abilities required for demanding tasks, as well as possible spatial learning and memory deficits. Knockout of Ntng2 in a cellular model resulted in short neurites, and knockout of its trans-synaptic partner Ngl2/Lrrc4 in mice revealed autistic-like behavior and reduced NMDAR synaptic plasticity. The Ngl2/Lrrc4-knockout mouse phenotype was rescued by NMDAR activation, suggesting a mechanistic link to autism spectrum disorder. We thus propose NTNG2 as a candidate disease gene and provide further support for the involvement of Netrin-G2 in neuropsychiatric phenotypes.

Homozygous stop-gain variant in LRRC32, encoding a TGFß receptor, associated with cleft palate, proliferative retinopathy, and developmental delay.

The transforming growth factor-beta (TGFß) signaling pathway is essential for palatogenesis and retinal development. Glycoprotein A repetitions predominant (GARP), encoded by LRRC32, is a TGFß cell surface receptor that has been studied primarily in the context of cellular immunity. We identified a homozygous stop-gain variant in LRRC32 (c.1630C>T; p.(Arg544Ter)) in two families with developmental delay, cleft palate, and proliferative retinopathy. Garp-null mice have palate defects and die within 24 h after birth. Our study establishes LRRC32 as a candidate disease-associated gene in humans and lends further support to the role of the TGFß pathway in palatogenesis and retinal development.

Biallelic variants in AGTPBP1, involved in tubulin deglutamylation, are associated with cerebellar degeneration and motor neuropathy.

The ATP/GTP-Binding Protein 1 (AGTPBP1) gene (OMIM *606830) catalyzes deglutamylation of polyglutamylated proteins, and its deficiency manifests by cerebellar ataxia and peripheral neuropathy in mice and lower motor neuron-like disease in sheep. In the mutant mice, cerebellar atrophy due to Purkinje cell degeneration is observed, likely due to increased tubulin polyglutamylation in affected brain areas. We report two unrelated individuals who presented with early onset cerebellar atrophy, developmental arrest with progressive muscle weakness, and feeding and respiratory difficulties, accompanied by severe motor neuronopathy. Whole exome sequencing followed by segregation analysis in the families and cDNA studies revealed deleterious biallelic variants in the AGTPBP1 gene. We conclude that complete loss-of-function of AGTPBP1 in humans, just like in mice and sheep, is associated with cerebellar and motor neuron disease, reminiscent of Pontocerebellar Hypoplasia Type 1 (PCH1).

Congenital myasthenic syndrome in Israel: Genetic and clinical characterization.

The objective of the study was to evaluate the epidemiology of patients with congenital myasthenic syndrome (CMS) in Israel. Targeted mutation analysis was performed based on the clinical symptoms and electrophysiological findings for known CMS. Additional specific tests were performed in patients of Iranian and/or Iraqi Jewish origin. All medical records were reviewed and clinical data, genetic mutations and outcomes were recorded. Forty-five patients with genetic mutations in known CMS genes from 35 families were identified. Mutations in RAPSN were identified in 13 kinships in Israel. The most common mutation was c.-38A>G detected in 8 patients of Iranian and/or Iraqi Jewish origin. Four different recessive mutations in COLQ were identified in 11 kinships, 10 of which were of Muslim-Arab descent. Mutations in CHRNE were identified in 7 kinships. Less commonly detected mutations were in CHRND, CHAT, GFPT1 and DOK7. In conclusion, mutations in RAPSN and COLQ are the most common causes of CMS in our cohort. Specific mutations in COLQ, RAPSN, and CHRNE occur in specific ethnic populations and should be taken into account when the diagnosis of a CMS is suspected.

Vaccine escape of piliated Streptococcus pneumoniae strains.

INTRODUCTION: Type1-pilus proteins were suggested as targets of future protein-based vaccines. Here we studied the effect of pneumococcal-conjugate vaccine (PCV7) implementation on the prevalence of piliated strains in a unique study setting which controls for typical confounders; the Palestinian-Israeli Collaborative Research (PICR). METHODS: Annual cross-sectional surveys of pneumococcal carriage were performed during 2009-2011 among two closely related population that live under different health policies (a) Palestinian-Authority (PA) (n=1773), where PCV7 was not yet introduced (b) East-Jerusalem (EJ) (n=983) where PCV7 was rapidly implemented. Clinical data were collected, pneumococci identified and characterized and the presence of Type1-pilus genes was determined by rrgC PCR. RESULTS: Following PCV7 implementation in EJ, overall carriage prevalence did not change (∼30%), but VT7 strains decreased from 61.5% to 33.8%. While prevalence of non-piliated-VT7 isolates decreased from 37% to 10%, p<0.001, the prevalence of piliated-VT7 strains persisted ∼25%. Additionally, piliated non-VT13 strains emerged (1-15%, p<0.001). These changes were not observed in PA. These dynamics were independent of the bacteria's resistance pattern. CONCLUSIONS: A differential effect of PCV7 was observed with a relative resistance of piliated strains to the vaccine. This suggests that Type1-pilus confers an intrinsic advantage for colonization and may be an attractive vaccine target.

Infantile neurodegenerative disorder associated with mutations in TBCD, an essential gene in the tubulin heterodimer assembly pathway.

Mutation in a growing spectrum of genes is known to either cause or contribute to primary or secondary microcephaly. In primary microcephaly the genetic determinants frequently involve mutations that contribute to or modulate the microtubule cytoskeleton by causing perturbations of neuronal proliferation and migration. Here we describe four patients from two unrelated families each with an infantile neurodegenerative disorder characterized by loss of developmental milestones at 9­24 months of age followed by seizures, dystonia and acquired microcephaly. The patients harboured homozygous missense mutations (A475T and A586V) in TBCD, a gene encoding one of five tubulin-specific chaperones (termed TBCA-E) that function in concert as a nanomachine required for the de novo assembly of the α/ß tubulin heterodimer. The latter is the subunit from which microtubule polymers are assembled. We found a reduced intracellular abundance of TBCD in patient fibroblasts to about 10% (in the case of A475T) or 40% (in the case of A586V) compared to age-matched wild type controls. Functional analyses of the mutant proteins revealed a partially compromised ability to participate in the heterodimer assembly pathway. We show via in utero shRNA-mediated suppression that a balanced supply of tbcd is critical for cortical cell proliferation and radial migration in the developing mouse brain. We conclude that TBCD is a novel functional contributor to the mammalian cerebral cortex development, and that the pathological mechanism resulting from the mutations we describe is likely to involve compromised interactions with one or more TBCD-interacting effectors that influence the dynamics and behaviour of the neuronal cytoskeleton.

Varied utilisation of health provision by Arab and Jewish residents in Israel.

INTRODUCTION: Provision of healthcare is considered a basic human right. Delivery and uptake is affected by many complex factors. Routine vaccinations are provided free of charge in Israel to all residents. The Palestinian Israeli Collaborative Research (PICR) group conducted research on vaccine impact at eight primary care facilities in east Jerusalem (EJ) and central Israel (IL) which allowed assessment and comparison of interactions of these Arab and Jewish populations, respectively, with healthcare services. METHODS: Families attending clinic with a child under five years old were invited to participate. Utilisation of healthcare was assessed using data from standardise questionnaires completed after enrolment, using proxies of vaccination status, antibiotic use, primary care physician and hospital visits as well as demographics such as household size. Differences between EJ and IL were assessed using chi squared tests; univariate analyses identified potential confounders which were tested in a multiple logistic regression model for any independent associations between region and outcome. RESULTS: Children in EJ were significantly more likely to live in larger households, with tobacco smokers, to have been breastfed, hospitalised and used antibiotics recently than those in IL, who were significantly more likely to have recently seen a primary care physician (all p < 0.01). Receipt of routine vaccinations, given at well baby clinics, was similar between the regions at above 95% (p = 0.11), except for influenza which was delivered separately at primary physician clinics to 5% (EJ) and 12% (IL). Receipt of pneumococcal vaccine when paid for separately was significantly higher in IL than EJ (3% vs 31%). Multivariate analysis identified the most important independent predictors of these differences as region, age and household size. CONCLUSIONS: Healthcare in Israel is of a very high standard, but it is not uniformly utilised within the community in all geographical areas, though in some key areas, such as uptake of most routine childhood vaccination, equality seems to be achieved. To ensure excellent healthcare is achieved across the population, inequalities must be addressed, for instance in health promotion and other activities, which could improve and normalise health outcomes.

Measuring the effects of pneumococcal conjugate vaccine (PCV7) on Streptococcus pneumoniae carriage and antibiotic resistance: the Palestinian-Israeli Collaborative Research (PICR).

BACKGROUND: The Palestinian-Israeli Collaborative Research (PICR) cross-conflict setting provided a unique opportunity to study overall and indirect effects of pneumococcal conjugate vaccine (PCV7), in two closely related Palestinian populations governed by two distinct health authorities with distinct vaccination policies. Here, PCV7 effects on pneumococcal carriage, serotype distribution and antibiotic resistance are reported. METHODS: Annual cross-sectional surveys of pneumococcal carriage were performed during 2009-2011 among Palestinian children (≤5 years) (a) under Palestinian-Authority (PA) health policy (Ramallah, Nablus and Bethlehem), where PCV7 was unlicensed (b) under Israeli health policy (East-Jerusalem (EJ)) where PCV7 was rapidly implemented from July 2009. Clinical data were collected, pneumococci identified and characterized for antibiotic susceptibilities and serotype. Analyses included multivariate logistic models with an interaction term for PCV7-effect. RESULTS: Altogether, 2755 children from PA (n=1772) and EJ (n=983) were enrolled, of which ~30% were pneumococcal carriers. While overall carriage was not affected by vaccination policy, carriage of vaccine-type (VT7) strains decreased from 52% to 22% (p<0.001) in EJ, where PCV was implemented, but not in PA. This was accompanied by an increase in non-VT13 strains from 34% to 65% (p<0.001) in EJ, but not in PA. Furthermore, within two years post-PCV7 introduction, proportion of multi-drug resistant strains, which was initially 23% in both populations, decreased significantly in EJ, to 10%, while simultaneously it increased in PA to 33% (p<0.001). Similar trends were observed for resistance to most antibiotic groups. The proportion of resistant isolates among non-VT13 strains did not change during the study period. CONCLUSIONS: The unique study design distinguishes secular and seasonal effects from true vaccine effects. While PCV7 did not affect overall pneumococcal carriage rate, VT7 strains, many of which were antibiotic resistant decreased and were replaced by non-VT13 strains, which were mostly not antibiotic resistant, resulting in a net decrease in antibiotic resistance.

Variable myopathic presentation in a single family with novel skeletal RYR1 mutation.

We describe an autosomal recessive heterogeneous congenital myopathy in a large consanguineous family. The disease is characterized by variable severity, progressive course in 3 of 4 patients, myopathic face without ophthalmoplegia and proximal muscle weakness. Absence of cores was noted in all patients. Genome wide linkage analysis revealed a single locus on chromosome 19q13 with Zmax = 3.86 at θ = 0.0 and homozygosity of the polymorphic markers at this locus in patients. Direct sequencing of the main candidate gene within the candidate region, RYR1, was performed. A novel homozygous A to G nucleotide substitution (p.Y3016C) within exon 60 of the RYR1 gene was found in patients. ARMS PCR was used to screen for the mutation in all available family members and in an additional 150 healthy individuals. This procedure confirmed sequence analysis and did not reveal the A to G mutation (p.Y3016C) in 300 chromosomes from healthy individuals. Functional analysis on EBV immortalized cell lines showed no effect of the mutation on RyR1 pharmacological activation or the content of intracellular Ca(2+) stores. Western blot analysis demonstrated a significant reduction of the RyR1 protein in the patient's muscle concomitant with a reduction of the DHPRα1.1 protein. This novel mutation resulting in RyR1 protein decrease causes heterogeneous clinical presentation, including slow progression course and absence of centrally localized cores on muscle biopsy. We suggest that RYR1 related myopathy should be considered in a wide variety of clinical and pathological presentation in childhood myopathies.

Lamotrigine overdose in a child.

The purpose of this article is to describe an unusual presentation of lamotrigine toxicity in an epileptic child treated on a lower than previously reported dosage. This is a case description of a 5-year-old epileptic girl on lamotrigine monotherapy, which caused toxicity. The child presented with ataxia, drowsiness, and acute confusion after ingesting 500 mg (25 mg/kg/d) in two 250-mg doses 12 hours apart. This was followed by vomiting and seizure exacerbation. Discontinuing lamotrigine, intravenous fluids and observation were the mainstays of therapy. Until now, the reported minimum dose of lamotrigine causing toxicity was 800 mg. In this patient, toxic manifestation occurred after the initial 250 mg. This case report demonstrates the low safety margin in children treated with lamotrigine.

Symptomatic myocardial bridging in a child without hypertrophic cardiomyopathy.

Myocardial bridging (MB) is a rare coronary anomaly in children that is typically associated with hypertrophic cardiomyopathy or left ventricular hypertrophy. Several reports, mainly in adults, have suggested an association between MB and sudden death or ischemia without other cardiac abnormalities. In this report, we describe an 11-year-old girl with syncope and manifestations of cardiac ischemia associated with MB of the middle segment of the left anterior descending artery. The coronary anomaly was not associated with left ventricular hypertrophy. Surgical unroofing of the affected coronary artery segment resulted in complete recovery. MB should be included in the differential diagnosis of children presenting with syncope and signs of ischemia even in the absence of ventricular hypertrophy.