Parental mosaicism in another case of Dravet syndrome caused by a novel SCN1A deletion: a case report

BACKGROUND: Dravet syndrome, a rare genetic disorder with early-onset epileptic encephalopathy, was first described by Dravet in 1978. Dravet syndrome is most frequently caused by various mutations of the SCN1A gene encoding the type 1 subunit of the neuronal voltage-gated sodium channel. CASE PRESENTATION: Two sisters of a non-consanguineous Palestinian family from the Arab community in Israel attended our child development and pediatric neurology clinic due to recurrent seizures and developmental delay. Genomic DNA was extracted from peripheral blood lymphocytes of all family members and a SCN1A mutation in exon 10 was revealed by Sanger sequencing in both affected siblings but not in the parents. Our data present a case of Dravet syndrome caused by a novel heterozygous SCN1A deletion (c.1458_1465delCTCTAAGT) in two affected siblings. Our findings add to the spectrum of mutations known in the SCN1A gene and confirm parental mosaicism as a mechanism relevant for transmission of this disease. CONCLUSIONS: These cases confirm parental mosaicism in the transmission of Dravet syndrome and add to the spectrum of known mutations of the SCN1A gene. Repeated reports on parental mosaicism should remind us that there is a risk of recurrence even if the mutation is apparently de novo.