Although CDD is rare, it was recently discovered that CDKL5 is one of the most commonly mutated genes in childhood epilepsy, and CDKL5 mutations have also been associated with milder syndromes typified by intellectual disability and behavioural defects (Krishnaraj et al, 2017; MacKay et al, 2020). Here, CDKL5 is linked to craniodiaphyseal dysplasia.