Pathological loss-of-function mutations in cyclin-dependent kinase-like 5 (CDKL5) (Weaving et al., 2004; Bahi-Buisson et al., 2012) cause CDKL5 deficiency disorder (CDD, OMIM 300203, 300672), a rare (incidence 1:40,000–60,000; Lindy et al., 2018; Kothur et al., 2018; Symonds, 2017) neurodevelopmental disorder associated with severe early-life epilepsy, motor, cognitive, visual, and autonomic disturbances (Bahi-Buisson et al., 2012; Bahi-Buisson et al., 2008; Nemos et al., 2009; Castrén et al., 2011; Melani et al., 2011; Fehr et al., 2015). This evidence concerns the gene CDKL5 and craniodiaphyseal dysplasia.