We present a patient with Rett syndrome (RTT; MECP2) and autosomal‐recessive succinic semialdehyde dehydrogenase deficiency (SSADHD; ALDH5A1 (aldehyde dehydrogenase 5a1 = SSADH), in whom the current phenotype exhibits features of SSADHD (hypotonia, global developmental delay) and RTT (hand stereotypies, gait anomalies). The gene discussed is MECP2; the disease is Rett syndrome.