Seven patients had a VUS, one in MECP2 and six in other genes related to intellectual disability and other features overlapping RTT: the aforementioned MADD in addition to DDX3X, KCNT1, SCN8A, SMC1A and STXBP1. The male patient had a VUS in MECP2 inherited from his apparently healthy mother. This evidence concerns the gene DDX3X and multiple acyl-CoA dehydrogenase deficiency.