The propositus (V-4) is a Moroccan 5 years old boy, non-consanguineous, last child of three siblings, and was addressed for familial epilepsy (Fig. 1A). His parents and older sister appear to be healthy and have been free of epilepsy seizure in the past. He had neonatal hypotonia, psychomotor delay, and no seating position with the support of the head at 2 years old. Daily-generalized seizures started at 8 months old and treated by valproate of sodium, but without any response. At clinical examination, he had stature and weight delay at <3rd percentile, microcephaly at -2SD, severe hypotonia, with no facial dysmorphia nor nystagmus. The computerized tomography (CT) scan was normal, but the electroencephalogram (EEG) showed abnormal waves at right fronto-temporal region. Unfortunately, MRI could not be available for the patient.Fig. 1a Pedigree of the studied Moroccan family with X-linked epileptic seizures, presenting the co-segregation of the c.251C > A mutation. The patient above the arrow indicates the proband. b Chromatograms by Sanger sequencing of family members who are hemizygous, heterozygous and wild-type for the PLP1 variant. c Amino acid conservation map across species demonstrating a highly conserved residues position 84 (based on Multiz Alignments Track of UCSC Genome Browser and The human genome reference hg19/GRCch37)