Evidence for genetic admixture as a determinant in the occurrence of insulin-dependent diabetes mellitus in U.S. blacks

In recent years, it has been proposed that genetic admixture may have played a role in the increased frequency of insulin-dependent diabetes mellitus (IDDM) in young U.S. blacks relative to African blacks. In support of this proposal, the similar associations of specific markers of the major histocompatibility complex (MHC) with IDDM in U.S. blacks with respect to U.S. whites have been cited. To determine whether racial admixture was a factor in the increased prevalence, we did three analyses of admixture. In the first we used nine genetic markers (ABO, Rh, Fy, Hp, Gc, Pl, OR, Tfr, and Gm) and determined that there was significantly greater than zero genetic contribution from whites in our sample of U.S. black IDDM patients (9.6 +/- 2.3%, P less than 0.01) when a sample of U.S. blacks without IDDM was used as one "parental" population. In the next two analyses, we estimated the amounts of genetic contribution from whites in the U.S. blacks with and without IDDM using reported gene frequencies for West African blacks for four genetic markers (ABO, Rh, Fy, and Hp). The estimate of admixture (21.4 +/- 2.8%) for the black IDDM sample was greater than that for the U.S. black controls (17.9 +/- 2.3%), although the difference was not significant. Our estimate of genetic contribution from whites, 21.4% for black IDDM patients, supports the assumptions of 20% admixture which MacDonald and Rotter and Hodge used to test their respective models for the inheritance of IDDM. These results support the hypothesis that admixture with the white population is, in part, responsible for the increase in prevalence of IDDM seen in U.S. blacks.

Associations of properdin factor B with melanoma

We investigated 98 melanoma patients and 135 normal controls for differences in phenotype and genotype frequencies at the properdin factor B locus. A significant negative association with the Bf-F allele and melanoma was found, resulting in an estimated relative risk of 0.5. The estimated relative risk for developing melanoma among people with the Bf-FF genotype is 0.07. The Bf-S phenotype was significantly increased among the melanoma sample, with an estimated risk of 6.5. The data suggest association of the Bf locus with a melanoma protection and/or susceptibility gene(s).

Properdin factor B polymorphism in Black Americans

Properdin factor B is a genetically-controlled polymorphism that can be demonstrated by agarose gel electrophoresis. The Bf gene frequencies were determined for 194 blacks from the south-eastern United States. The frequencies for Bf-F, Bf-S, Bf-F1, and Bf-S1 are 0.626, 0.034, and 0.013, respectively. The south-eastern blacks have similar Bf frequencies to the South African blacks; however, both these groups are different from blacks from Boston. The frequency differences between south-eastern blacks and Boston blacks may be due to racial admixture differences found in the two populations.