July 17, 2019

First Known Case of Double Somatic Mosaicism Reported in Girl with Dravet Syndrome

A genetic phenomenon called double somatic mosaicism was found for a first time in a girl with Dravet syndrome, a case study reports.

The study, “Double somatic mosaicism in a child with Dravet syndrome,” was published in Neurology Genetics.

Dravet syndrome, a severe type of epilepsy usually evident during the first year of life, is in about 80% of cases tied to known mutations in the SCN1A gene, which encodes for a sub-unit of a sodium channel called NaV1.1 that is involved in the transmission of electrical signals in the brain.

In about 20% of Dravet patients, however, the disorder’s cause  is unclear. In these cases, it has been proposed that genetic alterations taking place in very early fetal development, and not inherited from the parents, may be the underlying reason.

Investigators at the University of Washington examined whether somatic mosaicism — a phenomenon in which an individual has cells that are genetically different due to a mutation taking place during very early fetal development (shortly after the embryo formed) — could be the reason why some people develop idiopathic (unknown cause) Dravet syndrome.

They used a highly sensitive technique known as deep sequencing to analyze SCN1Aand seven other genes previously linked with the disease (SCN2A, SCN8A, HCN1, GABRA1, GABRG2, STXBP1, and PCDH19) using DNA they isolated from blood or saliva of 20 patients with this type of Dravet syndrome.

“We detected double mosaicism in SCN1A in a patient with Dravet syndrome. Comprehensive studies of disease-relevant tissue will be required to gain a more accurate picture of somatic mosaicism levels and how this affects disease severity,” the scientists concluded.

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