In 2008, we found the X-linked CASK gene (MIM 300172) to be mutated in female patients with a severe neurodevelopmental disorder and distinct brain anomalies which comprised progressive microcephaly, pontocerebellar hypoplasia and severe developmental delay (DD), named microcephaly with pontine and cerebellar hypoplasia (MICPCH, MIM 300749) [1]. Here, CASK is linked to microcephaly.