Survival of a male patient harboring CASK Arg27Ter mutation to adolescence.

Background: CASK is an X-linked gene in mammals and its deletion in males is incompatible with life. CASK heterozygous mutations in female patients associate with intellectual disability, microcephaly, pontocerebellar hypoplasia, and optic nerve hypoplasia, whereas CASK hemizygous mutations in males manifest as early infantile epileptic encephalopathy with a grim prognosis. Here, we report a rare case of survival of a male patient harboring a CASK null mutation to adolescent age. Methods: Trio whole exome sequencing analysis was performed from blood genomic DNA. Magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), and electroencephalogram (EEG) analyses were performed to determine anomalies in brain development, metabolite concentrations, and electrical activity, respectively. Results: Trio-WES analysis identified a de novo c.79C>T (p.Arginine27Ter) mutation in CASK causing a premature translation termination at the very N-terminus of the protein. The 17-years, and 11-month-old male patient displayed profound intellectual disability, microcephaly, dysmorphism, ponto-cerebellar hypoplasia, and intractable epilepsy. His systemic symptoms included overall reduced somatic growth, dysautonomia, ventilator and G tube dependence, and severe osteopenia. Brain MRI revealed a severe cerebellar and brain stem hypoplasia with progressive cerebral atrophy. EEG spectral analysis revealed a global functional defect with generalized background slowing and delta waves dominating even in the awake state. Conclusion: This case study is the first to report survival of a male patient carrying a CASK loss-of-function mutation to adolescence and highlights that improved palliative care could extend survival. Moreover, the genomic position encoding Arg27 in CASK may possess an increased susceptibility to mutations.