Mutations in the X‐linked gene CASK (OMIM: 300172) are associated with intellectual disability, microcephaly and pontocerebellar hypoplasia (Burglen et al., 2012; Hayashi et al., 2012; LaConte et al., 2018, 2019; Moog et al., 2011; Najm et al., 2008). Here, CASK is linked to microcephaly.