A total of 188,043 variants were detected. The WES data covered all exons of known X-Linked Epilepsy related genes, and no known pathogenic mutations were identified in these genes. Nevertheless, we identified a single hemizygous base substitution in coding exon3, c.251C > A of the PLP1 gene (based on GRCh37/hg19, and transcript ID NM_000533), resulting in substitution of alanine by an aspartic acid at amino acid 84. This mutation was found in hemizygous state in the propositus V-4 and in his cousin V-7. Sanger sequencing confirmed this mutation in hemizygous state in the affected subjects (V-9, V-10) and in heterozygous state in the obligatory carrier mothers, showing co-segregation of the mutation with the disease phenotype (Fig. 1A). The non-affected IV-12 was wild type for this mutation (Fig. 1B).