A novel missense variant in the CASK gene causes intellectual developmental disorder and microcephaly with pontine and cerebellar hypoplasia.

BACKGROUND: Variants in the CASK gene result in a wide range of observed phenotypes in humans, such as FG Syndrome 4 and intellectual disabilities. Intellectual developmental disorder with microcephaly and pontine and cerebellar hypoplasia (MICPCH) is an X-linked disorder that affects females and is characterized by severely impaired intellectual development and variable degrees of pontocerebellar hypoplasia. Variants in CASK are the main genetic cause of MICPCH. Variants in CASK can explain most patients with MICPCH, but there are still some patients whose disease aetiology cannot be explained.

CASE PRESENTATION: An 11-month-old female diagnosed with MICPCH exhibited general developmental delays, microcephaly, and cerebellar hypoplasia. Whole-exome sequencing (WES) was used to find a novel heterozygous missense variant (NM_003688.3: c.638T>G) of CASK in this patient. Strikingly, this variant reduced the expression of CASK at the protein level but not at the mRNA level. By using protein structure prediction analysis, this study found that the amino acid change caused by the variant resulted in further changes in the stability of the protein structure, and these changes caused the downregulation of protein expression and loss of protein function.

CONCLUSION: In this study, we first reported a novel heterozygous pathogenic variant and a causative mechanism of MICPCH. The amino acid change cause by this variant led to changes in the protein structure and a decrease in its stability, which caused a loss of protein function. This study could be helpful to the genetic diagnosis of this disease.