Of particular interest, inactivation of the X‐linked CDKL5 gene, or disease‐associated mutations commonly found in the N‐terminal CDKL5 catalytic domain, causes a neurodevelopmental disorder termed CDKL5 deficiency disorder (CDD; Tao et al, 2004; Weaving et al, 2004), which has some overlapping features with Rett syndrome (Scala et al, 2005) and West syndrome (Kalscheuer et al, 2003).§ The gene discussed is CDKL5; the disease is CDKL5 disorder.