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.

    13/100 (page IX)
    FOREWORD Both these papers start with an admirable method for distinguishing those cases of mental subnormality by which relevant aetiological factors are most likely to be identified. This is to select cases in which more than one member of the family group is affected. Dr. Davison's paper includes a very large number of cases carefully and meticulously identified. She starts with the well-known fact that the incidence of mental subnormality in males is higher than in females and that the disproportion increases as the intellectual level falls. Her conclusions are cautious, but impres¬ sive. She finds a remarkable excess of pedigrees which are compatible with X-linked inheritance, and goes on to point out something that might be expected, namely, that the data fit the hypothesis that there are two types of sibship, namely, those in which males are especially at risk and those in which the risk is equal for the two sexes. An important point she makes is that the data do not appear to fit the hypothesis of multifactorial inheritance, which would imply a higher threshold of susceptibility for females than males. A very interesting finding is that dermato- glyphic investigations show that the total ridge counts in the male affected families only are appreciably lower than in the families where both sexes are affected. Dr. Davison's conclusion is that there is a considerable contribution to the determination of severe mental subnormality by X-linked recessive genes. Apart from her findings and interpretations this publication will be of very great value to other workers because the basic data are set out at great length and in full detail. It is to be hoped that her work will stimulate other investigations, and it is certain that her findings will be discussed at length. The second contribution, by Dr. Peter N. Swift, Dr. Philip F. Benson and Dr. John D. Studdy, refers to a more minutely selected group. They studied cases at Leybourne Grange Hospital where the patient had an I.Q^. of 50 or less and a full sib with an I.Q,. of 60 or less. The total number, after appropriate exclusions, amounted to 30 sibships. In 10 families the siblings had similar physical abnormalities, for example, in one it was cerebral diplegia and in another probably Tay-Sachs disease. In no less than 5 of the remaining families the siblings had similar biochemical abnormalities. In one of these it was phenylketonuria but, in the other four, two or more of the retarded siblings excreted excessive amounts of the same amino acid. These are new entities, and it is remark¬ able that a study of this size should have picked up no less than four new biochemical abnor¬ malities associated with severe mental retarda¬ tion. It may well be that as knowledge grows the proportion of cases of presumable recessive inheritance which will be identified as due to a biochemical abnormality will increase. Once again, the sex difference appears. In the original 66 index cases (before the exclusion of six) there were 40 males and 26 females. Furthermore, of the 10 index patients whose heights were at least four standard deviations below the mean, all were males. One does feel, venturing a guess, that the influence of sex in mental subnormality will in the future require a lot of elucidation. In this paper, too, the individual findings are repeated at length and will be of the greatest value to future investigators. J. A. Fraser Roberts, C.B.E., M.D., D.Sc., F.R.c.p., F.R.s. Geneticist, Paediatric Research Unit, Cameron House, Guy's Hospital Medical School, London SE I gRT. ix