CDKL5 and Rett syndrome: In the following reports, mutations in CDKL5 were commonly identified in patients clinically diagnosed with the early seizure variant of RTT and it was only in 2013 that the pathology associated with CDKL5 deficiency was established as an independent clinical entity referred to as CDKL5 disorder [6] or, lately, as CDKL5 deficiency disorder (CDD).