CASK aberrations in male patients with Ohtahara syndrome and cerebellar hypoplasia

Purpose: Ohtahara syndrome (OS) is one of the most severe and earliest forms of epilepsy. STXBP1 and ARX mutations have been reported in patients with OS. In this study, we aimed to identify new genes involved in OS by copy number analysis and whole exome sequencing.

Methods: Copy number analysis and whole exome sequencing were performed in 34 and 12 patients with OS, respectively. Fluorescence in situ hybridization, quantitative polymerase chain reaction (PCR), and breakpoint-specific and reverse-transcriptase PCR analyses were performed to characterize a deletion. Immunoblotting using lymphoblastoid cells was done to examine expression of CASK protein.

Key findings: Genomic microarray analysis revealed a 111-kb deletion involving exon 2 of CASK at Xp11.4 in a male patient. The deletion was inherited from his mother, who was somatic mosaic for the deletion. Sequencing of the mutant transcript expressed in lymphoblastoid cell lines derived from the patient confirmed the deletion of exon 2 in the mutant transcript with a premature stop codon. Whole exome sequencing identified another male patient who was harboring a c.1A>G mutation in CASK, which occurred de novo. Both patients showed severe cerebellar hypoplasia along with other congenital anomalies such as micrognathia, a high arched palate, and finger anomalies. No CASK protein was detected by immunoblotting in lymphoblastoid cells derived from two patients.

Significance: The detected mutations are highly likely to cause the loss of function of the CASK protein in male individuals. CASK mutations have been reported in patients with intellectual disability with microcephaly and pontocerebellar hypoplasia or congenital nystagmus, and those with FG syndrome. Our data expand the clinical spectrum of CASK mutations to include OS with cerebellar hypoplasia and congenital anomalies at the most severe end.