Mutations in the gene encoding the Methyl-CpG binding protein 2 (MECP2) underlies Rett syndrome, a neurodevelopmental disorder presented with mental retardation, autistic behavior, compromised sensory sensations and loss of previously acquired cognitive milestones, including purposeful hand use and expressive language, in young females. The gene discussed is MECP2; the disease is atypical Rett syndrome.