Whole-exome sequencing confirms implication of VPS13D as a potential cause of progressive spastic ataxia

International audienceBackground: VPS13D is a large ubiquitin-binding protein playing an essential role in mitophagy by regulating mitochondrial fission. Recently, VPS13D biallelic pathogenic variants have been reported in patients displaying variable neurological phenotypes, with an autosomic recessive inheritance. The objectives of the study were to determine the genetic etiology of a patient with early onset sporadic progressive spastic ataxia, and to investigate the pathogenicity of VPS13D variants through functional studies on patient's skin fibroblasts. Case presentation: We report the case of a 51-year-old patient with spastic ataxia, with an acute onset of the disease at age 7. Walking difficulties slowly worsened over time, with the use of a wheelchair since age 26. We have used trio-based whole-exome sequencing (WES) to identify genes associated with spastic ataxia. The impact of the identified variants on mitochondrial function was assessed in patient's fibroblasts by imaging mitochondrial network and measuring level of individual OXPHOS complex subunits. Compound heterozygous variants were identified in VPS13D: c.946C > T, p.Arg316* and c.12416C > T, p.(Ala4139Val). Primary fibroblasts obtained from this patient revealed an altered mitochondrial morphology, and a decrease in levels of proteins from complex I, III and IV. Conclusions: Our findings confirmed implication of VPS13D in spastic ataxia and provided further support for mitochondrial defects in patient's skin fibroblasts with VPS13D variants. This report of long-term follow up showed a slowly progressive course of the spastic paraplegia with cerebellar features. Furthermore, the performed functional studies could be used as biomarker helping diagnosis of VPS13D-related neurological disorders when molecular results are uneasy to interpret

Expanding the Spectrum of Neurological Manifestations in Cutis Laxa, Autosomal Recessive, Type IIIA

International audienceCutis laxa is a heterogeneous group of diseases, characterized by abundant and wrinkled skin and a variable degree of intellectual disability. Cutis laxa, autosomal recessive, type IIIA and autosomal dominant 3 syndromes are caused by autosomal recessive or de novo pathogenic variants in ALDH18A1. Autosomal recessive variants are known to lead to the most severe neurological phenotype, and very few patients have been described.We describe a 13-month-old patient with cutis laxa, autosomal recessive, type IIIA, with an extremely severe phenotype, including novel neurological findings. This description enlarges the neurological spectrum associated to cutis laxa, autosomal recessive, type IIIA, and provides an additional description of this syndrome

Major intra-familial phenotypic heterogeneity and incomplete penetrance due to a CACNA1A pathogenic variant

IF 2.004 (2017)International audienceThe CACNA1A gene encodes a calcium-dependent voltage channel, localized in neuronal cells. Pathogenic variants in this gene are known to lead to a broad clinical spectrum including episodic ataxia type 2, spinocerebellar ataxia type 6, familial hemiplegic migraine, and more recently epileptic encephalopathy. We report a large family revealing a wide variability of neurological manifestations associated with a CACNA1A missense pathogenic variant. The index case had early-onset epileptic encephalopathy with progressive cerebellar atrophy, although his mother and his great-grandmother suffered from paroxystic episodic ataxia. His grandfather and great grand-aunt reported no symptoms, but two of her sons displayed early-onset ataxia with intellectual disability. Two of her little daughters suffered from gait disorders, and also from epilepsy for one of them. All these relatives were carriers of the previously described heterozygous variant in CACNA1A gene. We report here the first family leading to major clinical variability and incomplete penetrance. Our family highlights the difficulties to provide accurate genetic counselling concerning prenatal diagnosis regarding highly variable severity of the clinical presentation

Rare variants in the GABAA receptor subunit epsilon identified in patients with a wide spectrum of epileptic phenotypes

BACKGROUND: Epilepsy belongs to a group of chronic and highly heterogeneous brain disorders. Many types of epilepsy and epileptic syndromes are caused by genetic factors. The neural amino acid y-aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the mammalian central nervous system. It regulates activity of channel pores by binding to transmembrane GABA-receptors (GABRs). The GABRs are heteropentamers assembled from different receptor subunits (alpha1-6, beta1-3, gamma1-3, delta, epsilon, theta, pi, and rho1-3). Several epileptic disorders are caused by mutations in genes encoding single GABRs. METHODS: We applied trio- and single-whole exome sequencing to search for genetic sequence variants associated with a wide range of epileptic phenotypes accompanied by intellectual disability and/or global developmental delay in the investigated patients. RESULTS: We identified four hemizygous sequence variants in the GABAA receptor subunit epsilon gene (GABRE), including one nonsense (NM_004961.3: c.399C>A, p.Tyr133*), two missense variants (NM_004961.3: c.664G>A, p.Glu222Lys; NM_004961.3: c.1045G>A, p.Val349Ile), and one variant affecting the translation initiation codon (NM_004961.3: c.1A>G, p.Met1?) in four unrelated families. CONCLUSION: Our clinical and molecular genetic findings suggest that GABRE is a likely candidate gene for epilepsy. Nevertheless, functional studies are necessary to better understand pathogenicity of the GABRE-mutations and their associations with epileptic phenotypes

Early-onset epileptic encephalopathy related to germline PIGA mutations: A series of 5 cases

International audienceThe molecular diagnosis of early-onset epileptic encephalopathy (EOEE), an expanding field in child neurology, is becoming increasingly possible thanks to the widespread availability of next-generation sequencing and whole-exome sequencing. In the past 15 years, mutations in STXBP1, KCNQ2, SCN2A, SCN8A and numerous other genes have been reported, giving a more accurate insight for these rare diseases. Among these genes, germline mutations in Phosphatidyl Inositol Glycan A (PIGA) gene were first reported in 2012. Located on Xp22.2, PIGA is involved in the synthesis of GPI (glycosylphosphatidylinositol) which acts as a membrane anchor for different proteins: enzymes, adhesion molecules, regulation of the complement way, and co-receptor in transduction signal. Children suffering from this condition exhibit developmental delay with early-onset epilepsy, severe dysmorphic signs, multi-visceral anomalies and early death in the most severe forms. Here, we report five cases of germline PIGA mutations, with two missense mutations that have not been reported to date. We provide a new insight into the electroclinical phenotype. At the onset, epileptic spasms and focal-onset seizures with upper limbs and ocular involvements were present. Epilepsy proved pharmacoresistant in 4 out of 5 cases. Interictal EEG may be normal at the onset of epilepsy, but abnormalities in electroencephalographic studies were eventually present in all cases. Different types of seizures may be present simultaneously, and epileptic phenotypes evolve with aging

De novo coding variants in the AGO1 gene cause a neurodevelopmental disorder with intellectual disability

Background: High-impact pathogenic variants in more than a thousand genes are involved in Mendelian forms of neurodevelopmental disorders (NDD). Methods: This study describes the molecular and clinical characterisation of 28 probands with NDD harbouring heterozygous AGO1 coding variants, occurring de novo for all those whose transmission could have been verified (26/28). Results: A total of 15 unique variants leading to amino acid changes or deletions were identified: 12 missense variants, two in-frame deletions of one codon, and one canonical splice variant leading to a deletion of two amino acid residues. Recurrently identified variants were present in several unrelated individuals: p.(Phe180del), p.(Leu190Pro), p.(Leu190Arg), p.(Gly199Ser), p.(Val254Ile) and p.(Glu376del). AGO1 encodes the Argonaute 1 protein, which functions in gene-silencing pathways mediated by small non-coding RNAs. Three-dimensional protein structure predictions suggest that these variants might alter the flexibility of the AGO1 linker domains, which likely would impair its function in mRNA processing. Affected individuals present with intellectual disability of varying severity, as well as speech and motor delay, autistic behaviour and additional behavioural manifestations. Conclusion: Our study establishes that de novo coding variants in AGO1 are involved in a novel monogenic form of NDD, highly similar to the recently reported AGO2-related NDD