A biologic and genetic study of 40 cases of severe pure mental retardation

Abstract

The family history of 40 patients with severe "pure" mental retardation (MR) was studied to determine the incidence of mental retardation and dull-normal intelligence among relatives, probable etiologies and an empiric recurrence risk. Significant findings include: (1) an increased sex ratio (69% males) of propositi, (2) a significant proportion of patients with clinical manifestations besides MR, (3) virtually no consanguinity among parents, (4) a "positive" family history for over 1/2 of the propositi--about 37% of all children in the sibships were affected; about 21% of the full sibs were affected, (5) a higher number of offspring produced by dull persons and a lower number of offspring from retarded persons compared to two normal persons (6) a proportionately large number of affected children produced from matings involving one or two dull persons, (7) a tendency for dull to have additional dull children and mentally retarded parents to have further retarded children while normal parents with more than one affected child usually had further retarded children, (8) an incidence of affected parents of about 32%, and (9) an overall empiric recurrence risk of 14%. Several etiologies were discussed as possible causes of the condition(s) in this group: (unrecongized) environmental damage and/or maternal/fetal interaction; unrecognized chromosome abnormalities; the homozygous state of several different autosomal recessive gees: X-linked recessive mutations; autosomal dominat new mutations; and mutifactoral inheritance. It was concluded that the group was etiologically heterogeneous and although none of the probable etiologies could be excluded, it seemed reasonable to assume that autosomal recessive inheritance plays an important role in the etiology of severe "pure" mental retardation.

Familial risk and heritability of intellectual disability: a population‐based cohort study in Sweden

“…There are four main findings from our investigation. First, our 20-years risk and frequency of ID in full-siblings are comparable to old reports (Angeli & Kirman, 1975;Becker et al, 1977;Bundey & Carter, 1974;Bundey et al, 1989;Costeff & Weller, 1987;Durkin et al, 1976;Herbst & Baird, 1982;Laxova, Ridler, Bowen-Bravery, & Opitz, 1977;Turner et al, 1971;Turner & Partington, 2000). Now, we provide estimates with narrow confidence intervals also for halfsiblings and other relatives.…”

Sib risks for nonspecific mental retardation in British Columbia

“…However, because the cases were identified through special clinics or facilities, it is likely that only a small, and likely biased, sample of the affected in the population was actually ascertained. For this reason, the risk figures such as the 14% recurrence risk of severe MR with no associated anomalies reported by Becker et a1 [1977] or the 20% risk to sibs for MR with microcephalus reported by Opitz et a1 [Opitz, 1977;Opitz et al, 19781 may be overestimates.…”

“…In some of these studies, as well as the diagnostidgenetic study at the Central Wisconsin Colony and Training School [Kaveggia, Opitz, and Pallister, 197 1 ;Kaveggia et al, 1975;Opitz, 1977Opitz, , 1979Opitz et al, 19781, the MR cases were differentiated by associated anomalies or neurological dysfunction. The risk calculations from all of these investigations were based on the assumption of complete ascertainment in a population.…”

An etiological survey of the severely retarded Hertfordshire children who were born between January 1, 1965 and December 31, 1967

“…The 36 propositi in the Central Wisconsin Colony series analyzed in detail by Becker et al (1977a) had 9 affected sibs out of a total of 66 born after the birth of the propositi, suggesting a relatively high empiric recurrence risk of about 14%. There were no known subsequently affected sibs in the families of children in Table IV; however, the numbers are small, and furthermore, not all parents have comDleted their families.…”