MECP2 and nervous system disorder: Duplications of genomic segments containing the MECP2 gene and hence increased MeCP2 protein dosage led to a severe neurological disorder, the MECP2 duplication syndrome, which is 100% penetrant in affected males and is associated with infantile hypotonia, severe autistic features, poor speech development, recurrent infections, progressive spasticity, and developmental regression4, 5.