Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD; OMIM 300672), also known as early infantile epileptic encephalopathy 2, is characterized by severe early-onset drug-resistant epilepsy with motor, cognitive, visual, and autonomic disturbances resulting from nonfunctional or absent CDKL5 protein1. This evidence concerns the gene CDKL5 and epilepsy.