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Genetic influences on mild mental retardation: concepts, findings and research implications

Published online by Cambridge University Press:  31 July 2008

Michael Rutter ,
Emily Simonoff  and
Robert Plomin
Michael Rutter
Affiliation:
Social, Genetic and Developmental Psychiatry Research Centre, and MRC Child Psychiatry Unit, Institute of Psychiatry, De Crespigny Park, Denmark Hill, London SE5 8AF
Emily Simonoff
Affiliation:
Social, Genetic and Developmental Psychiatry Research Centre, and MRC Child Psychiatry Unit, Institute of Psychiatry, De Crespigny Park, Denmark Hill, London SE5 8AF
Robert Plomin
Affiliation:
Social, Genetic and Developmental Psychiatry Research Centre, and MRC Child Psychiatry Unit, Institute of Psychiatry, De Crespigny Park, Denmark Hill, London SE5 8AF
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Extract

It has long been known that mild mental retardation (meaning that associated with an IQ in the 50–69 range) shows a strong tendency to run in families and that there is a much increased recurrence risk if either a parent or a sib has mental retardation. For example, Reed & Reed (1965) found that, having had one retarded child, the chance of a further retarded child was 6% if both parents and their sibs were ‘normal’, 13% if both parents were normal but one had a retarded sib, 20% if one parent was retarded, and 42% if both were retarded. A somewhat similar gradient was found in the more recent study by Bundey, Thake & Todd (1989). The appreciation that mild mental retardation was so strongly familial had led Lewis (1933) some years earlier to refer to it as ’subcultural‘ (meaning that it was a normal variation), in order to differentiate it from severe mental retardation, which was viewed as ‘pathological’. Penrose (1938, 1963) made the same classificatory distinction and the utility of a two-group approach became generally accepted (Burack, 1990).

Type
Session 3: Genetic Issues
Information
Journal of Biosocial Science , Volume 28 , Special Issue 4: Proceedings of the Galton Institute Symposium on Biological and Social Aspects of Intelligence , October 1996 , pp. 509 - 526
Copyright
Copyright © Cambridge University Press 1996

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