Genetics of psychoses
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The financial burden of the psychoses each year runs into the billions of dollars while the misery to everyone concerned is beyond calculation. It should be self-evident that the genetics of the psychoses is therefore a topic worth much more consideration than it has received. One egg twins are genetically identical but about half of the time when one of the twins has a psychosis the other one does not display it. The difference in expression must be due to environmental causes. However, the fact that identical twins are concordant for a psychosis about 4 times as often as fraternal twins indicates that there is an important genetic basis for the psychoses. The existence of a genetic basis for the psychoses is also demonstrated by a study of the relatives of a psychotic person. This is the major interest of this paper. Any study of the genetics of psychoses is complicated by numerous variables such as different ages of onset for the various disorders, the lower fertility of psychotic males compared with psychotic females, and our finding that the offspring of psychotic mothers have about twice as high a risk of developing a psychosis as do the offspring of psychotic fathers. A large variable category is that of the environment, though no clues emerged from our study as to what aspects of the environment are involved in the onset of the psychoses. The beneficial effects of tranquilizers and other improvements in treatment have reduced the length of time spent in hospitals by psychotic persons and have reduced their disadvantage in reproduction. Our model shows that if for schizophrenia the disadvantage disappeared there could be a maximum 10 per cent increase in the frequency of schizophrenia in the coming generation. However, it is unlikely that present treatments will result in completely normal reproductive rates for psychotic persons. If a completely preventative treatment for the psychoses should be discovered, there should be an increase in the frequencies of the genes for the psychoses. But this undesired increase in the genes for the psychoses would be balanced off by the reduction in the number of persons actually suffering from the miseries of their mental disorder. It is our conclusion that the functional psychoses have an important genetic basis, that it is multigenic and not strikingly different in nature from that for other quantitative genetic traits.