Double somatic mosaicism in a child with Dravet syndrome

Abstract

Dravet syndrome, the prototypic infantile-onset developmental and epileptic encephalopathy, occurs secondary to de novo pathogenic variants in SCN1A in over 80% of cases1. One possible genetic etiology for patients without a heterozygous SCN1A mutation is a post-zygotic mosaic SCN1A variant below the level detected by diagnostic sequencing, which routinely identifies only variants with allele frequencies above ∼20%. We used targeted deep resequencing to systematically investigate whether mosaicism could be the cause in individuals with molecularly unsolved Dravet syndrome.