Early manifestations of Rett syndrome are primarily psychomotor retardation. Rett syndrome is a disease caused by mutations in sex chromosome genes. It is a neurodevelopmental disorder that seriously affects the psychomotor development of children, and can lead to abnormalities in intelligence, movement, behavior, and spirit. Early symptoms of Rett syndrome usually appear in the first 6 to 18 months of life, and children with psychomotor developmental delay are characterized by mental retardation, slow growth of head circumference, disturbed sleep rhythms, and clumsiness in sitting or crawling motor functions. For children suspected of having clinical symptoms of Rett syndrome, parents are advised to seek early medical attention from a specialized pediatrician or neurologist for a definitive diagnosis to avoid delays.