Case report: Homozygous PRRT2 mutation in ICCA Egyptian family with reduced penetrance

Infantile convulsions and choreoathetosis (ICCA) syndrome is a rare neurological genetic disorder inherited in an autosomal dominant manner with incomplete penetrance. It is characterized by the association of benign infantile seizures (BIS) at age 3-12 months with paroxysmal kinesigenic choreoathetosis (PKC) later in life. Mutations in proline-rich transmembrane protein 2 (PRRT2) gene have been recently identified as the main cause of ICCA and other related disorders. Few ICCA cases with homozygous mutations have been reported, where they exhibited more severe clinical phenotype including intellectual disability. Here we report two Egyptian siblings with ICCA whose molecular analysis of PRRT2 revealed homozygous c.649dupC mutation. However, they have not developed any physical or cognitive disabilities. Moreover, their parents, who found to be heterozygous for the mutation, did not display any of the disease phenotype during their infancy and childhood. Low penetrance and variable expressivity of ICCA could be attributed to specific genetic modifiers and/or environmental factors that require further investigations to be identified.