Eighty RTT adult female patients harboring a pathogenic MECP2 mutation were randomly assigned to treatment to MTZ for insomnia and mood disorders (mean age = 23.1 ± 7.5 years, range = 16–47 years; mean MTZ-treatment duration = 1.64 ± 1.0 years, range = 0.08–5.0 years). The gene discussed is MECP2; the disease is insomnia.