BRAT1 encephalopathy: a recessive cause of epilepsy of infancy with migrating focal seizures.

Epilepsy of infancy with migrating focal seizures (EIMFS), one of the most severe developmental and epileptic encephalopathy syndromes, is characterized by seizures that migrate from one hemisphere to the other. EIMFS is genetically heterogeneous with 33 genes. We report five patients with EIMFS caused by recessive BRAT1 variants, identified via next generation sequencing. Recessive pathogenic variants in BRAT1 cause the rigidity and multifocal seizure syndrome, lethal neonatal with hypertonia, microcephaly, and intractable multifocal seizures. The epileptology of BRAT1 encephalopathy has not been well described. All five patients were profoundly impaired with seizure onset in the first week of life and focal seizure migration between hemispheres. We show that BRAT1 is an important recessive cause of EIMFS with onset in the first week of life, profound impairment, and early death. Early recognition of this genetic aetiology will inform management and reproductive counselling.

The role of sodium channels in sudden unexpected death in pediatrics.

BACKGROUND: Sudden Unexpected Death in Pediatrics (SUDP) is a tragic event, likely caused by the complex interaction of multiple factors. The presence of hippocampal abnormalities in many children with SUDP suggests that epilepsy-related mechanisms may contribute to death, similar to Sudden Unexplained Death in Epilepsy. Because of known associations between the genes SCN1A and SCN5A and sudden death, and shared mechanisms and patterns of expression in genes encoding many voltage-gated sodium channels (VGSCs), we hypothesized that individuals dying from SUDP have pathogenic variants across the entire family of cardiac arrhythmia- and epilepsy-associated VGSC genes. METHODS: To address this hypothesis, we evaluated whole-exome sequencing data from infants and children with SUDP for variants in VGSC genes, reviewed the literature for all SUDP-associated variants in VGSCs, applied a novel paralog analysis to all variants, and evaluated all variants according to American College of Medical Genetics and Genomics (ACMG) guidelines. RESULTS: In our cohort of 73 cases of SUDP, we assessed 11 variants as pathogenic in SCN1A, SCN1B, and SCN10A, genes with long-standing disease associations, and in SCN3A, SCN4A, and SCN9A, VGSC gene paralogs with more recent disease associations. From the literature, we identified 82 VGSC variants in SUDP cases. Pathogenic variants clustered at conserved amino acid sites intolerant to variation across the VGSC genes, which is unlikely to occur in the general population (p < .0001). For 54% of variants previously reported in literature, we identified conflicting evidence regarding pathogenicity when applying ACMG criteria and modern population data. CONCLUSION: We report variants in several VGSC genes in cases with SUDP, involving both arrhythmia- and epilepsy-associated genes. Accurate variant assessment as well as future studies are essential for an improved understanding of the contribution of sodium channel-related variants to SUDP.

Mutations in NRXN1 and NRXN2 in a patient with early-onset epileptic encephalopathy and respiratory depression.

Early infantile epileptic encephalopathy (EIEE) is a severe disorder associated with epilepsy, developmental delay and intellectual disability, and in some cases premature mortality. We report the case of a female infant with EIEE and strikingly suppressed respiratory dysfunction that led to death. Postmortem research evaluation revealed hypoplasia of the arcuate nucleus of the medulla, a candidate region for respiratory regulation. Genetic evaluation revealed heterozygous variants in the related genes NRXN1 (c.2686C>T, p.Arg896Trp) and NRXN2 (c.3176G>A, p.Arg1059Gln), one inherited from the mother with family history of sudden infant death syndrome (SIDS) and one from the father with family history of febrile seizures. Although there are no previous reports with the digenic combination of NRXN1 and NRXN2 variants, patients with biallelic loss of NRXN1 in humans and double neurexin 1α/2α knockout mice have severe breathing abnormalities, corresponding to the respiratory phenotype of our patient. These observations and the known interaction between the NRXN1 and NRXN2 proteins lead us to hypothesize that digenic variants in NRXN1 and NRXN2 contributed to the phenotype of EIEE, arcuate nucleus hypoplasia, respiratory failure, and death.