Aetiology in severe and mild mental retardation: a population-based study of Norwegian children

摘要: The aetiology of mental retardation (MR) was studied in a population-based series Norwegian children derived from 30 037 born between 1980 and 1985. study included 178 children, 79 with severe MR (SMR) (IQ<50) 99 mild (MMR) (IQ 50 to 70). Aetiology divided into two main groups: biopathological unspecified. group comprised 96% SMR 68% MMR, subdivided prenatal (70% 51%), perinatal (4% 5%), postnatal damage (5% 1%), undetermined timing the damaging event (18% 11%). Single-gene disorders accounted for 15 63 genetic disorders, including X-linked recessive six. During course study, at least 27 (15%) had their aetiological diagnosis revised. Gestational age <32 weeks, birthweight <1500 g, Apgar scores 0 2 1 5 minutes implied significantly increased risk MR, but contributed only 4% study. Decreased (1500 2499 g) 3 6 showed probability MR. Despite extensive investigations, 32% MMR were not identified any biological markers considered as unspecified several most probably representing lower end normal IQ distribution population.