MILD MENTAL RETARDATION IN CHILDREN IN A NORTHERN SWEDISH COUNTY

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Abstract
A series of children with mild mental retardation (171 children, IQ 59-69) born in 1959-1970 in a northern Swedish county and registered by the Board for Provisions and Services to the Mentally Retarded was analyzed retrospectively. The mean annual incidence of mild mental retardation in registered children alive at the age of 1 yr decreased during the period 1959-1970 and for the whole period was 4.2/1000, compared with 3.9/1000 for severe mental retardation in the same period of time and area. Ten children once classified as mildly mentally retarded made considerable intellectual progress and after some time no longer needed special help from the authorities. There was a pronounced male excess in the total series (1.8:1) and in all the main etiological groups. Only small differences were found in mean birth weights, gestational age and maternal age in the main etiological groups. In the series as a whole there was an increased frequency of children small for gestational age. Prenatal causes were considered relevant in 43%, perinatal in 7% and postnatal in 5%. In 2% there was a psychosis. In 43% the etiology could not be traced. Genetic causes were found in 31%; in 8% there was a chromosomal etiology, in a further 8% a mutant gene disorder and in 15% the etiology were considered multifactorial, i.e., at least 1 first degree relative also had mental retardation and in both cases the cause of the retardation was unknown. Thirty percent of the children had associated CNS handicaps, epilepsy (16%) being the most frequent.