Bi-allelic genetic variants in the translational GTPases GTPBP1 and GTPBP2 cause a distinct identical neurodevelopmental syndrome.

The homologous genes GTPBP1 and GTPBP2 encode GTP-binding proteins 1 and 2, which are involved in ribosomal homeostasis. Pathogenic variants in GTPBP2 were recently shown to be an ultra-rare cause of neurodegenerative or neurodevelopmental disorders (NDDs). Until now, no human phenotype has been linked to GTPBP1. Here, we describe individuals carrying bi-allelic GTPBP1 variants that display an identical phenotype with GTPBP2 and characterize the overall spectrum of GTP-binding protein (1/2)-related disorders. In this study, 20 individuals from 16 families with distinct NDDs and syndromic facial features were investigated by whole-exome (WES) or whole-genome (WGS) sequencing. To assess the functional impact of the identified genetic variants, semi-quantitative PCR, western blot, and ribosome profiling assays were performed in fibroblasts from affected individuals. We also investigated the effect of reducing expression of CG2017, an ortholog of human GTPBP1/2, in the fruit fly Drosophila melanogaster. Individuals with bi-allelic GTPBP1 or GTPBP2 variants presented with microcephaly, profound neurodevelopmental impairment, pathognomonic craniofacial features, and ectodermal defects. Abnormal vision and/or hearing, progressive spasticity, choreoathetoid movements, refractory epilepsy, and brain atrophy were part of the core phenotype of this syndrome. Cell line studies identified a loss-of-function (LoF) impact of the disease-associated variants but no significant abnormalities on ribosome profiling. Reduced expression of CG2017 isoforms was associated with locomotor impairment in Drosophila. In conclusion, bi-allelic GTPBP1 and GTPBP2 LoF variants cause an identical, distinct neurodevelopmental syndrome. Mutant CG2017 knockout flies display motor impairment, highlighting the conserved role for GTP-binding proteins in CNS development across species.

The clinical and genetic landscape of developmental and epileptic encephalopathies in Egyptian children.

Developmental and epileptic encephalopathies (DEEs) are a heterogeneous group of epilepsies characterized by early-onset, refractory seizures associated with developmental regression or impairment, with a heterogeneous genetic landscape including genes implicated in various pathways and mechanisms. We retrospectively studied the clinical and genetic data of patients with genetic DEE who presented at two tertiary centers in Egypt over a 10-year period. Exome sequencing was used for genetic testing. We report 74 patients from 63 unrelated Egyptian families, with a high rate of consanguinity (58%). The most common seizure type was generalized tonic-clonic (58%) and multiple seizure types were common (55%). The most common epilepsy syndrome was early infantile DEE (50%). All patients showed variable degrees of developmental impairment. Microcephaly, hypotonia, ophthalmological involvement and neuroimaging abnormalities were common. Eighteen novel variants were identified and the phenotypes of five DEE genes were expanded with novel phenotype-genotype associations. Obtaining a genetic diagnosis had implications on epilepsy management in 17 patients with variants in 12 genes. In this study, we expand the phenotype and genotype spectrum of DEE in a large single ethnic cohort of patients. Reaching a genetic diagnosis guided precision management of epilepsy in a significant proportion of patients.

Spondyloenchondrodysplasia in five new patients: identification of three novel ACP5 variants with variable neurological presentations.

Spondyloenchondrodysplasia (SPENCD) is an immune-osseous disorder caused by biallelic variants in ACP5 gene and is less commonly associated with neurological abnormalities such as global developmental delay, spasticity and seizures. Herein, we describe five new patients from four unrelated Egyptian families with complex clinical presentations including predominant neurological presentations masking the skeletal and immunological manifestations. All our patients had spasticity with variable associations of motor and mental delay or epilepsy. All except for one patient had bilateral calcification in the basal ganglia. One patient had an associated growth hormone deficiency with fair response to growth hormone therapy (GH) where the height improved from -3.0 SD before GH therapy to -2.35 SD at presentation. Patients had different forms of immune dysregulation. All patients except for one had either cellular immunodeficiency (3 patients) or combined immunodeficiency (1 patient). Whole exome sequencing was performed and revealed four ACP5 variants: c.629C > T (p.Ser210Phe), c.526C > T (p.Arg176Ter), c.742dupC (p.Gln248ProfsTer3) and c.775G > A (p.Gly259Arg). Of them, three variants were not described before. Our study reinforces the striking phenotypic variability associated with SPENCD and expands the mutational spectrum of this rare disorder. Further, it documents the positive response to growth hormone therapy in the studied patient.

Brain monoamine vesicular transport disease caused by homozygous SLC18A2 variants: A study in 42 affected individuals.

PURPOSE: Brain monoamine vesicular transport disease is an infantile-onset movement disorder that mimics cerebral palsy. In 2013, the homozygous SLC18A2 variant, p.Pro387Leu, was first reported as a cause of this rare disorder, and dopamine agonists were efficient for treating affected individuals from a single large family. To date, only 6 variants have been reported. In this study, we evaluated genotype-phenotype correlations in individuals with biallelic SLC18A2 variants. METHODS: A total of 42 affected individuals with homozygous SLC18A2 variant alleles were identified. We evaluated genotype-phenotype correlations and the missense variants in the affected individuals based on the structural modeling of rat VMAT2 encoded by Slc18a2, with cytoplasm- and lumen-facing conformations. A Caenorhabditis elegans model was created for functional studies. RESULTS: A total of 19 homozygous SLC18A2 variants, including 3 recurrent variants, were identified using exome sequencing. The affected individuals typically showed global developmental delay, hypotonia, dystonia, oculogyric crisis, and autonomic nervous system involvement (temperature dysregulation/sweating, hypersalivation, and gastrointestinal dysmotility). Among the 58 affected individuals described to date, 16 (28%) died before the age of 13 years. Of the 17 patients with p.Pro237His, 9 died, whereas all 14 patients with p.Pro387Leu survived. Although a dopamine agonist mildly improved the disease symptoms in 18 of 21 patients (86%), some affected individuals with p.Ile43Phe and p.Pro387Leu showed milder phenotypes and presented prolonged survival even without treatment. The C. elegans model showed behavioral abnormalities. CONCLUSION: These data expand the phenotypic and genotypic spectra of SLC18A2-related disorders.

Novel LSS variants in alopecia and intellectual disability syndrome: New case report and clinical spectrum of LSS-related rare disease traits.

Pathogenic biallelic variants in LSS are associated with three Mendelian rare disease traits including congenital cataract type 44, autosomal recessive hypotrichosis type 14, and alopecia-intellectual disability syndrome type 4 (APMR4). We performed trio research exome sequencing on a family with a four-year-old male with global developmental delay, epilepsy and striking alopecia, and identified novel compound heterozygous LSS splice site (c.14+2T>C) and missense (c.1357 G>A; p.V453L) variant alleles. Rare features associated with APMR4 such as cryptorchidism, micropenis, mild cortical brain atrophy and thin corpus callosum were detected. Previously unreported APMR4 findings including cerebellar involvement in the form of unsteady ataxic gait, small vermis with prominent folia, were noted. A review of all reported variants to date in 29 families with LSS-related phenotypes showed an emerging genotype-phenotype correlation. Our report potentially expands LSS-related phenotypic spectrum and highlights the importance of performing brain imaging in LSS-related conditions.

Clinical and molecular spectrum of a large Egyptian cohort with ALS2-related disorders of infantile-onset of clinical continuum IAHSP/JPLS.

This study presents 46 patients from 23 unrelated Egyptian families with ALS2-related disorders without evidence of lower motor neuron involvement. Age at onset ranged from 10 months to 2.5 years, featuring progressive upper motor neuron signs. Detailed clinical phenotypes demonstrated inter- and intrafamilial variability. We identified 16 homozygous disease-causing ALS2 variants; sorted as splice-site, missense, frameshift, nonsense and in-frame in eight, seven, four, three, and one families, respectively. Seven of these variants were novel, expanding the mutational spectrum of the ALS2 gene. As expected, clinical severity was positively correlated with disease onset (p = 0.004). This work provides clinical and molecular profiles of a large single ethnic cohort of patients with ALS2 mutations, and suggests that infantile ascending hereditary spastic paralysis (IAHSP) and juvenile primary lateral sclerosis (JPLS) are belonged to one entity with no phenotype-genotype correlation.

Neurodevelopmental disorder in an Egyptian family with a biallelic ALKBH8 variant.

Alkylated DNA repair protein AlkB homolog 8 (ALKBH8) is a member of the AlkB family of dioxygenases. ALKBH8 is a methyltransferase of the highly variable wobble nucleoside position in the anticodon loop of tRNA and thus plays a critical role in tRNA modification by preserving codon recognition and preventing errors in amino acid incorporation during translation. Moreover, its activity catalyzes uridine modifications that are proposed to be critical for accurate protein translation. Previously, two distinct homozygous truncating variants in the final exon of ALKBH8 were described in two unrelated large Saudi Arabian kindreds with intellectual developmental disorder and autosomal recessive 71 (MRT71) syndrome (MIM# 618504). Here, we report a third family-of Egyptian descent-harboring a novel homozygous frame-shift variant in the last exon of ALKBH8. Two affected siblings in this family exhibit global developmental delay and intellectual disability as shared characteristic features of MRT71 syndrome, and we further characterize their observed dysmorphic features and brain MRI findings. This description of a third family with a truncating ALKBH8 variant from a distinct population broadens the phenotypic and genotypic spectrum of MRT71 syndrome, affirms that perturbations in tRNA biogenesis can contribute to neurogenetic disease traits, and firmly establishes ALKBH8 as a novel neurodevelopmental disease gene.

A founder mutation in PEX12 among Egyptian patients in peroxisomal biogenesis disorder.

At least 14 distinctive PEX genes function in the biogenesis of peroxisomes. Biallelic alterations in the peroxisomal biogenesis factor 12 (PEX12) gene lead to Zellweger syndrome spectrum (ZSS) with variable clinical expressivity ranging from early lethality to mildly affected with long-term survival. Herein, we define 20 patients derived from 14 unrelated Egyptian families, 19 of which show a homozygous PEX12 in-frame (c.1047_1049del p.(Gln349del)) deletion. This founder mutation, reported rarely outside of Egypt, was associated with a uniformly severe phenotype. Patients showed developmental delay in early life followed by motor and mental regression, progressive hypotonia, unsteadiness, and lack of speech. Seventeen patients had sparse hair or partial alopecia, a striking feature that was not noted previously in PEX12. Neonatal cholestasis was manifested in 2 siblings. Neurodiagnostics showed consistent cerebellar atrophy and variable white matter demyelination, axonal neuropathy in about half, and cardiomyopathy in 10% of patients. A single patient with a compound heterozygous PEX12 mutation exhibited milder features with late childhood onset with gait disturbance and learning disability. Thus, the PEX12 relatively common founder mutation accounts for the majority of PEX12-related disease in Egypt and delineates a uniform clinical and radiographic phenotype.

Dandy-Walker Malformation in a Girl with DDX3X-Related Intellectual Disability.

Introduction: We report on a 4-year-old female patient who presented with severe intellectual disability, autistic features, hyperlaxity of joints, and progressive scoliosis. Whole-exome sequencing identified a de novo missense variant (c.976C>T; p.Arg326Cys) in DDX3X. Case Presentation: The girl was born with congenital diaphragmatic hernia a finding which had not previously been associated with variants in DDX3X. Her brain MRI showed hypogenesis of corpus callosum, ventriculomegaly, frontal and perisylvian polymicrogyria, and hypoplastic pons in addition to Dandy-Walker malformation. Conclusion: Our results confirmed the phenotype and genotype correlation of missense variants and the polymicrogyria. Moreover, it further expands the knowledge of the phenotypic and molecular features of DDX3X-related intellectual disability.

Registry of ocular anomalies among patients with genetic disorders attending the clinical genetics department at the National Research Center in Egypt.

BACKGROUND: The congenital abnormalities of eyes are a major cause of visual impairment throughout the world. Prevention of visual impairment due to congenital and infantile abnormalities of eyes is very important. The aim of this study is to evaluate the frequency and types of congenital ocular anomalies among patients with genetic disorders. PATIENTS AND METHODS: This is a retrospective study that was conducted in the National Research Center, Egypt at the Clinical Genetics Department over a 4-year period. Out of 2500 patients attending the outpatient clinics, a total of 61 patients with congenital ocular malformations (2.44%) were included in this study. They underwent clinical and genetic assessments. RESULTS AND CONCLUSIONS: Isolated ocular malformations were found in 70.5% while complex ocular anomalies were found in 29.5%. A total of 37.7% of the patients had a known recognizable syndrome, 24.6% of the patients were classified as having metabolic disorders and 37.7% of the patients were classified as having isolated disorders. Chromosomal abnormalities were found in 4.9% of the patients. Congenital cataract was the most frequent feature in syndromic, metabolic, and isolated disorders. Our study elucidates the significance of the early detection of ocular anomalies for appropriate diagnosis of genetic disorders.