Somatic Mosaicism of PCDH19 in a male with early infantile epileptic encephalopathy and review of the literature.

Early infantile epileptic encephalopathy-9 (EIEE9) linked to mutations of the PCDH19 gene on the X chromosome was once thought to only affect females. Clinical features of the mutation include early onset of variable types and frequency of recurrent cluster of seizures, mild to profound intellectual disability, autistic traits, psychiatric features, and behavioral disturbances. PCDH19 pathogenic variants usually occur via an unusual X-linked pattern where heterozygous females are affected, but hemizygous males are asymptomatic. Somatic mosaic males for PCDH19 mutations are affected with EIEE9; since this discovery, four somatic mosaic males have been reported. We report the fifth confirmed male with somatic mosaicism of a novel pathogenic variant c.2147+2 T>C located in the splice site of Intron 1 of the PCDH19 gene, which continues to support that cellular interference is responsible for the pathogenic mechanism. The importance of our report is to provide significant knowledge about this rare cause of epilepsy in males, guide subsequent functional studies on males portraying an EIEE9 phenotype that have been potentially misdiagnosed, targeted therapeutic approaches, and further elucidation of this complex and interesting genetic disorder.