Although the clinical manifestations of individuals with the CDKL5 mutation closely resemble some features of Rett syndrome (RTT) [1], including hand stereotypies, autistic-like features, scarce acquisition of language and conscious hand use, it has now become clear that CDD represents an independent clinical entity with unique characteristics [2, 3]. The gene discussed is CDKL5; the disease is craniodiaphyseal dysplasia.