Bayat, Allan

Abstract Objective Biallelic pathogenic MBOAT7 variants are associated with neurodevelopmental disorders, intellectual disability (ID), epilepsy, and neuropsychiatric disorders such as attention‐deficit/hyperactivity disorder and autism spectrum disorders. We aimed to characterize the epilepsy phenotype in a cohort of patients affected by this syndrome. Methods We describe epilepsy features, electroencephalography, magnetic resonance imaging (MRI) findings, antiseizure treatment response, and neurodevelopment of 15 patients with biallelic MBOAT7 variants. Results All 15 patients had ID or developmental delay (DD). Twelve suffered from epilepsy, with mean age at seizure onset of 36 months (range = 2 months–6.5 years) and 10 of 12 showing signs of DD before seizure onset. Patients with epilepsy presented with focal motor seizures with impaired awareness ( n = 3), focal tonic–clonic seizures and epileptic spasms ( n = 1), focal to bilateral tonic–clonic seizures ( n = 1), unknown onset bilateral tonic–clonic seizures ( n = 2), myoclonic seizures ( n = 4), myoclonic–atonic seizures ( n = 1), atonic seizures ( n = 1), tonic seizures ( n = 1), and myoclonic absences ( n = 2). Seizure freedom was achieved in 66.7% (8/12), with variable antiseizure treatment regimes. We reviewed electroencephalograms of the patients with epilepsy. Background activity was normal in 64%, whereas 36% had either a generalized or a focal slowing. Interictal epileptiform discharges (IEDs) were reported in 83%. Generalized spikes/polyspikes were found in 53%, multifocal IEDs in 23%, and parasagittal focal IEDs in 26%. The most frequent abnormal brain MRI findings, reported in 58% of patients, included high‐intensity signal in T2 and fluid‐attenuated inversion recovery (FLAIR) sequences in dentate nuclei and globus pallidus. Biallelic missense variants seemed to be associated with better cognitive and motor outcomes compared to truncating variants and in‐frame deletions. Significance Biallelic MBOAT7 variants are associated with global developmental impairment in all affected patients and epilepsy in the majority. The seizure semiology is heterogenous. One third of our cohort had persistent seizures despite treatment. The most frequent MRI findings were hyperintensities in T2/FLAIR sequences in dentate nuclei and globus pallidus.

Abstract Objective Dravet syndrome (DS) is a developmental and epileptic encephalopathy. Diagnosis is clinical, but ~90% of patients have pathogenic variants in SCN1A . ATP6V0C has recently been proposed as a novel candidate gene for epilepsy, with or without developmental delay. Here we describe two adult patients with a clinical diagnosis of DS associated with ATP6V0C variants. Methods Patients with developmental and epileptic encephalopathies were evaluated by physicians who are experts in DS, and their clinical diagnosis was correlated with genetic findings. A subgroup of those patients with DS but without known genetic causes were evaluated through gene panels, whole exome sequencing, and chromosome microarray. Phenotype was determined by pediatric and adult chart reviews, interviews, and physical examinations. Results Of 753 patients with DS, two unrelated individuals with classic features of DS during childhood and adulthood were identified with heterozygous de novo missense variants in ATP6V0C (c.319G > C, p.(Gly107Arg) and c.284C > T, p.(Ala95Val), respectively). Both variants were absent in normal populations and computational prediction algorithms suggested deleterious effects on protein structure and/or function. No disease‐causing variants in other genes previously associated with DS were found. Significance Here we describe two adult patients with Dravet‐like syndrome and pathogenic/likely pathogenic variants in ATP6V0C . We propose that abnormal ATP6V0C function can, at the severe end of the clinical spectrum, be associated with Dravet‐like phenotype. This is relevant, as these patients would not qualify for disease‐modifying antisense nucleotide or gene therapies targeting SCN1A .