The twin-family method in psychiatric genetics illustrated from the investigations of Franz J. Kallmann.

Abstract

The present paper is aimed to celebrate Franz J. Kallmann's memory, by illustrating the twin-family method, which he developed. His phenomenal powers of organization are testified to by his extensive samples. Their representative nature has the built-in check of the ratio of MZ: DZ twins. He brought a refinement of his own to the existing methods of calculating expectancy from nett figures, that permits comparison of studies of varying age distributions relative to manifestation period. His investigative design allows not only for the standard global concordance comparisons between DZ and MZ twins as well as for those reared together and apart, but exploits the implications of the hitherto neglected comparison of the categories of sibs and DZ twins also. Further, his combined twin-family method comprehends in its extended range the powerful analytical tool of comparative figures for the series step-sibs, half-sibs, sibs, DZ twins and MZ twins (Kallmann and Sander, 1947; Kallmann, 1953). Kallmann (1954a, 1954b) has moreover given minute attention to controversies concerning legitimate inferences from twin studies, and has drawn attention to a point made by Darlington (1953), which is often overlooked by the best of geneticists. Discordance between MZ twins is not a measure merely of postnatal or even of prenatal environmental effects: it may also have a genetic component through the action of genes sensitive to cytoplasmic asymmetry.