Unusual combination of epilepsy phenotypes and a SCNM1 mutation in a three-generational family: photosensitivity, persistent at high age, and talking induced myoclonic jaw- jerks.

Abstract

We analysed the clinical phenotypes, evolution, and genetics of a large family presented through a single proband who suffered increasingly from jerks in her jaw especially when speaking in front of the classroom and who appeared to be photosensitive, both clinically and in EEG recordings. The proband was then investigated by Whole Exome Sequencing, which identified 4 novel, predicted damaging mutations in different genes, all located in one of the four linkage peaks. An Arg267Cys mutation in the SCNM1 gene was carried in heterozygous state in all photosensitive family members. The gene regulates splicing of voltage gated ion channels and the mutation indeed affected the level of splicing of the SCN1A splice variant that was also carried by 7 of the affected family members. No other SCNM1 mutations were found in unrelated PPR European patients, suggesting that SCNM1 is a private mutation of this family and may be causing this unique combination of phenotypes