Although CDKL5 disorder shares several features with Rett Syndrome, a neurodevelopmental disorder caused by mutations in the X-linked MECP2 gene [2], recent work assessing data from 86 subjects has argued that it should be considered a distinct clinical entity, primarily due to its early onset and lack of clinical regression following a period of normal development [3]. The gene discussed is CDKL5; the disease is Rett syndrome.