ETIOLOGIC FACTORS AND PREVALENCE OF SEVERE MENTAL-RETARDATION IN CHILDREN IN A SWEDISH MUNICIPALITY - THE POSSIBLE ROLE OF CONSANGUINITY

The prevalence of severe mental retardation (SMR) was studied in one o f the 24 suburban municipalities in Stockholm. The study area had a hi gh proportion of non-European nationals. The study population comprise d 14138 children born between 1979 and 1992 who resided in this munici pality on the census das, 31 December 1995. The total prevalence of SM R was 4.5 per 1000, being 3.7 per 1000 and 5.9 per 1000 in the Europea n and in the non-European population, respectively. The majority of ca ses (66%) had a definite prenatal origin. Down syndrome was the cause in 20%. Six families (10%) had at least two children with SMR. It was concluded that the prevalence was higher than in previous Swedish stud ies. Many cases were attributed to genetic factors. Consanguineous mar riages were assumed to be a factor of importance in the distribution o f aetiologies. Demographic differences between areas in Sweden must be considered when planning habilitation services.