The recurrence risks for mild idiopathic mental retardation.

Abstract

SUMMARY A genetic study of children attending ESN(M) schools in Coventry has shown a recurrence risk of idiopathic mental retardation in sibs lying between 1 in 4 and 1 in 5. There was also a prevalence of mental retardation in other relatives that was greater than the population prevalence, and was less for second degree relatives than for first degree, and less still for third degree relatives. Recurrence in sibs was greater if more than one first degree relative was affected. There was no suggestion of a contribution by X linked genes, once the fragile X syndrome had been excluded. The presence of perinatal and other environmental factors in the index children did not alter the recurrence risk for sibs except for very low birth weight. There was a low recurrence rate of mental retardation in Asian families, suggesting that they had a different distribution of intelligence from non-Asian families.

Risk Factors of Mental Retardation in Children Attending an Educationally Subnormal/Mental School in Dammam, Saudi Arabia

“…The higher prevalence of mental retardation in siblings of the MR group in this study is similar to those of Bundey et al [31] who also observed that the risk was higher the greater the degree of closeness to the index case. Hagberg et al [32] found that 29% of the untraceable causes of mildly mentally retarded children (IQ 50 to 70) had familial predisposition -"close relative with below average intelligence.…”

Evaluation of mental retardation: Recommendations of a consensus conference

“…It is generally preferable to defer assignment of a specific diagnosis rather than to establish an incorrect diagnosis. Valuable information regarding timing of the insult and the likely recurrence risk may sometimes be inferred in the course of a thorough evaluation, even in the absence of a specific causal diagnosis [Bartley and Hall, 1978;Bundey, 1989].Several approaches strongly influence the diagnostic yield in the evaluation of an individual with MR. Most importantly, the participants wished to stress the importance of serial evaluations of an individual over time.…”

Monogenic X-linked mental retardation: Is it as frequent as currently estimated? The paradox of the ARX (Aristaless X) mutations

“…It should be noted that one study failed to find a significant impact of X-linked genes in 'mild idiopathic MR', apart from fragile X. 8 If monogenic XLMR was to account for an excess of 30% of mentally retarded males over females, and forgetting the case where XLMR can lead to MR, albeit generally milder, in females (as in fragile X syndrome), or even leads to MR almost exclusively in females, such as for Rett syndrome, one would expect that 23% of MR in males is caused by XLMR. As discussed by Stevenson et al, 1 several clinical studies reported that XLMR accounts only for 5 -8% of male MR, but it is possible that nonsyndromic XLMR was underestimated in such studies, since it cannot be diagnosed in sporadic cases.…”