MARK2 and craniodiaphyseal dysplasia: Mutations in the X-linked CDKL5 gene, which encodes a serine-threonine kinase, consist of missense, nonsense, or frame-shift mutations (Hector et al., 2017); a few cases with genomic duplications including CDKL5 have been reported to have a clinical outcome that partially overlaps that of CDD (Szafranski et al., 2015).