Etiological survey on intellectual disability in the northern Finland birth cohort 1986.

The etiology of intellectual disability was studied both in incident (n = 9,432) and prevalent (n = 9,351) populations in a one-year birth cohort born in Northern Finland in 1985-1986. Data from multiple sources were used to follow the children until the age of 11.5 years. Of the incident cases (n=119) with intellectual disabilities, 66.4% had etiologically biomedical associative factor. Paranatal factors were relatively fewer and prenatal more common compared with earlier studies. We found nearly double the prevalence of genetic factors leading to intellectual disabilities compared with a contemporary study from Norway. The differences between the populations, despite random variation, some dissimilarities between etiological categorization and diagnostic accuracy, are in most part due to true differences between the study populations and genetic pool.