Prevalence, aetiology and comorbidity of severe and profound intellectual disability in Finland.

BACKGROUND: The aim of the present study was to describe the aetiology, associated impairments and prevalence of severe and profound intellectual disability (SPID) in Finland.
METHODS: The number of people with SPID in the catchment area of the Pääjärvi Centre for the Mentally Retarded, Lammi, Finland, (total population = 341,227) was calculated from the client register of this centre. Aetiological factors and background diagnoses for all subjects with SPID were analysed retrospectively.
RESULTS: The number of people with SPID was 461, giving a prevalence of 0.13%. The aetiology of their SPID was genetic or congenital in 235 (50.9%) individuals, acquired in 89 (19.3%), genetic and/or acquired in 84 (18.3%), and unknown in 53 (11.5%) subjects. Out of the 53 individuals with an SPID of unknown origin, 48 (90.6%) had an associated impairment; the remaining five were the only members of the study group showing normal growth, and having neither dysmorphic features, physical abnormalities nor family members with ID. Out of the 461 subjects, 422 (91.5%) had between one and six associated impairments (total = 954), and the remaining 39 (8.5%) had SPID as their only impairment. Uncomplicated SPID was mainly of genetic or congenital origin, whereas all subjects with acquired encephalopathy had multiple disabilities. Speech defects, epilepsy and cerebral palsy were the most common associated impairments.
CONCLUSIONS: Severe and profound ID almost always occurs concomitantly with other severe neurological or psychiatric impairments. The proportion of people with SPID described in the present study is similar to that found in Finland in 1966. The aetiology of SPID in the vast majority of cases is biopathological.