[Epidemiological study on the etiology of mental retardation].
D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D004314:Down Syndrome / Q000150:complications; D005260:Female; D006801:Humans; D008607:Intellectual Disability / Q000453:epidemiology / Q000209:etiology*; D007564:Japan; D008297:Male; D012640:Seizures / Q000150:complications; D012737:Sex Factors