Comparison across disorders found commonalities in the top caregiver concerns between Classic RTT, Atypical RTT, MECP2 Duplication Syndrome, CDKL5 Deficiency Disorder, and FOXG1 Syndrome; however, distinct differences in caregiver concerns between these disorders are consistent with the relative prevalence and impact of specific clinical features. This evidence concerns the gene CDKL5 and Down syndrome.