The cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a rare developmental and epileptic encephalopathy that is caused by mutations in the CDKL5 gene, which encodes a serine/threonine kinase that is essential for neuronal development, synapse formation, and axonal growth. Here, CDKL5 is linked to craniodiaphyseal dysplasia.