Genetic studies in mental subnormality.

Date:
1973
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Genetic studies in mental subnormality. Source: Wellcome Collection.

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    CHAPTER m Patterns of Distribution of Cases of Idiopathic Severe Mental Defect by Sex in 141 Families In 141 families severe mental defect in at least two individuals was considered to be idiopathic. These families were classified according to whether only males (50), only females (21) or both males and females (70) were affected (Table II). The families were further sub- grouped when there was pedigree evidence suggestive of X-linkage, the parents of affected individuals were consanguineous, or affected sibs had certain physical anomalies in common but which were not known to be due to any identifiable syndrome. Summarized information on these families is given in Appendix II. Data of the type indicated in Table III are not easy to analyse. Two-generation data can only be considered on first principles by pedigree analysis and, unless the data are very extensive and the mode of ascertainment can be strictly defined, there are pitfalls in attempting formal analyses of sibships in isolation. Bearing in mind that the aim of this study was to find whether there was evidence to suggest a contribution to male cases by X-linked recessive genes, a number of approaches seemed possible. In general, if all causes of defect applied equally to both sexes, then (a) equal numbers of males and females would be affected, (b) there would be approximately equal numbers of families with only males and only females affected, and (c) they would be outnumbered by the families with both sexes affected. The excess of families with both sexes affected would depend on the average number of affected per family. If, as we know, there is a marked excess of males with severe mental subnormality, then we should expect there to be more families with males only affected than those with females only affected. However, there is no satisfactory method, with the amount of data available, of estimating the proportion of all-male families expected for a given male/female ratio. This proportion could only be estimated if a large amount of data were available with varying numbers of affected and unaffected individuals. There are, however, other facets of the data which can be examined separately, and this will be done as follows. First, the families where only males were affected will be examined for Table II Classification of 141 families with idiopathic severe subnormality by clinical findings and sex No. of families No. of families No. of families with both males with only males with only and females Total affected females affected affected (a) Pedigree evidence suggestive of X-linkage ......... 8 — — 8 (b) Parents of at least two members were consanguineous . . . . . . i — 4 5 (c) Affected members had clinical similarities in common .... 6 3 2 11 (d) Remaining families ...... 35 18 64 117 Total ..... 50 21 70 141 7