CDKL5 and craniodiaphyseal dysplasia: Last but not the least, functional studies aimed to characterize the impact of CDKL5 mutations from patient-derived cell types (including brain organoids) will be pivotal to establish the impact of mutations and to dissect individual disease mechanism(s), to explain the broad heterogeneity in terms of neurodevelopmental and epileptic presentations of the affected patients and to assess the influence of additional genetic and non-genetic factors on phenotypical outcomes of CDD.