Abstract
In order to elucidate the genetic mechanism of the association between IDDM and HLA, through a comparison of expected frequencies and observed frequencies on the assumption of linkage equilibrium, it was assumed that the “deviation” between the two was due to the effect of epistasis and an attempt was made to estimate the epistatic variance. It was found that the ratio of epistatic variance to genotypic variance was 1/69 between IDDM and HLA-Bw 54, 1/59 between IDDM and HLA-DYT, and 1/33 between IDDM and HLA-DRw 4, all being comparatively low.
Since linkage disequilibrium is defined by the gamete frequency immediately prior to fertilization, even if epistasis were present, it does not necessarily imply that linkage disequilibrium would appear. The distance between these two loci must be smaller than a certain range.
Since the genetic character of man cannot be analyzed at the gamete level, in the present study genotypic epistasis is assumed and not linkage disequilibrium. Thus, linkage equilibrium, if actually present, can be detected. However, because epistasis and linkage disequilibrium make their appearance similar to a certain degree, this point should be given due consideration.
Elucidation of epistasis between IDDM and HLA is of extreme importance from the standpoint of clinical genetics. We therefore plan in the future to collect for review a larger volume of data under a more detailed plan.
