Mental retardation is not seen in -

Prenatal factors 1. Metabolic i) Aminoaciduria-phenylketonuria, homocystinemia, histidinemia, organic aciduria ii) Galactosemia iii) Mucopolysaccharidosis iv)Inherited degenerative disorders of the central nervous system 2. Chromosomal disorders. Down's syndrome, Fragile X syndrome, Klinefelter 3. Environment and nutrition gaps, iodine deficiency 4. Neuroectodermal dysplasia. Tuberous sclerosis. 5. Developmental defects. Microcephaly, craniostenosis, cretinism, porencephaly. 6. Maternal factors i) Use of teratogenic drugs in the first trimesters of pregnancy ii) Infections such as rubella, toxoplasmosis, cytomegalic inclusion disease, herpes syphilis and HIV. iii) Placental insufficiency iv)Toxemia of pregnancy v) Antepartum hemorrhage vi)Radiation during pregnancy Natal factors Birth injuries   3. Intracerebral hemorrhage Hypoxic, ischemic encephalopathy Postnatal factors Infections of central nervous system.  Meningoencephalitis 2. Head injuries 3. Hypoxia 4. Cerebrovascular. Thrombosis of cerebral vessels 5. Post-vaccinal encephalopathies 6. Kemicterus 7. Hypoglycemia 8. Malnutrition 9. Child abuse  10. Autism