The median age of epilepsy onset was much earlier in females with the CDKL5 disorder (6.0 weeks) than Rett syndrome (4.9 years) (Fig. 4) and the risk of developing seizures was much greater in CDKL5 affected females (log rank test p <0.001) during the observation period. Here, CDKL5 is linked to atypical Rett syndrome.