An intronic variant in BRAT1 creates a cryptic splice site, causing epileptic encephalopathy without prominent rigidity

Acta Neurol Belg. 2020 Dec;120(6):1425-1432. doi: 10.1007/s13760-020-01513-0. Epub 2020 Oct 10.

Abstract

BRAT1-related neurodevelopmental disorders are characterized by heterogeneous phenotypes with varying levels of clinical severity. Since the discovery of BRAT1 variants as the molecular etiology of lethal neonatal rigidity and multifocal seizure syndrome (RMFSL, OMIM 614498), these variants have also been identified in patients with milder clinical forms including neurodevelopmental disorder with cerebellar atrophy and with or without seizures (NEDCAS, OMIM 618056), epilepsy of infancy with migrating focal seizures (EIMFS), and congenital ataxia (CA). This study aims to examine the consequences and pathogenicity of a novel homozygous splice site variant in BRAT1 in a patient presenting with migrating focal seizures since birth without prominent rigidity. The patient was born from a consanguineous marriage and has had seizures since the neonatal period. He presented with dysmorphic features, pontocerebellar hypoplasia, and migrating focal seizures. Despite supportive treatment, his symptoms rapidly progressed to intractable myoclonic seizures, bouts of apnea and bradycardia, and arrest of head growth, with no acquisition of developmental milestones. Clinical exome sequencing yielded a novel homozygous splice variant in BRAT1. Genetic analysis based on reverse transcription of the patient's RNA followed by PCR amplifications performed on synthesized cDNA and Sanger sequencing was undertaken, and the functional effect of a BRAT1 variant on splicing machinery was demonstrated for the first time. The severe clinical presentation of migrating focal seizures and pontocerebellar hypoplasia in the absence of rigidity further expands the genotypic and phenotypic spectrum of BRAT1-related neurodevelopmental disorders.

Keywords: BRAT1; Migrating focal seizure; Pontocerebellar hypoplasia; Splice variant.