MECP2 and atypical Rett syndrome: This involved clinicians from the International Foundation for CDKL5 Research Centers of Excellence (COE) consortium and the National Institutes of Health' Rett Syndrome, MECP2 Duplication Disorder, and Rett- Related Disorders Natural History study consortium (U54 HD061222; ClinicalTrials.gov: NCT00299312/ NCT02738281).