Genetics
Review of New Aspects of Human Genetics, edited by C. E. Ford and Harry Harris. British Medical Bulletin, vol. 25, n. 1, Jan. 1969
British Journal of Psychiatry, 115, 1969, p. 736
This paper‑backed volume of reviews of recent advances in human genetics contains many papers of interest to psychiatrists. An over‑view of the ground covered is provided by L. S. Penrose in his introduction, and he points out some of the lessons that we may learn: the difficulty of separating the effects of heredity from those of the environment, the applicability of models in which an extreme of quantitative variation may lead to pathological effects, the need to pass beyond the polygenic explanation if the data for analysis are available: 'Whenever a locus is found with a great many alleles, which have quantitative measurements, it is difficult to distingush its effects from a continuous distribution resermbling the Gaussian model… there are twenty difleent variant forms of glucose‑6‑phosphate dehydrogenise enzyme, which are equivalent to twenty alleles in traditional genetics. Consequently some apparently polygenic traits may be controlled by single loci.'
This statement bases itself on the work of Harry Harris, who has shown in some beautiful studies the immense number and variety of genetical differences, such that one can assume each one of us has a unique enzyme constitution as much as a unique antigeisic one.
Of special interest to the reviewer are the papers of J. H. Edwards and C. O. Carter. Carter's discussion of the genetics of common disorders is highly relevant to our views about the hereditary contribution to the aetiology of schizophrenia and manic‑depression. Polygenic causation can be taken as proven in several fairly common congenital abnormalities, not least from Carter's own work, and highly probable in others. An exceedingly interesting feature of these conditions, which is as yet unexplained, is that there is a marked sex preponderance in one sex or the other. Thus there is a male preponderance in pyloric stenosis (sex ratio m/f 5•0), talipes equinovarus (2•0) and cleft lip (1•8), and a female preponderance in spina bifida cystica (0•8), anencephaly (0•4) and congenital dislocation of the hip (0•15). This would suggest that polygenic inheritance is more probable in manic‑depression, with a marked female preponderance, than in schizophrenia, with sex equality. Carter discusses the tests that may be applied to familial data to distinguish expectations based on a polygeniic from those based on a monogenic model. These possibilities are fruitful in ideas for future research.
The paper by Edwards has wit as well as wisdom, and is an important discussion along mathematical lines of the polygenic model, and what one means by the concept of heritability which is derived from it. His ideas will be of particular interest to workers concerned with any of the common disorders (such as the psychiatric ones) which unfortunately are a good deal more refractory to genetical analysis than conditions which are rare or very rare.