Properdin factor B polymorphism in Black Americans

Complotypes in individuals of African origin: frequencies and possible extended MHC haplotypes

We analyzed the frequency distribution of 106 complotypes [four allele sets of the major histocompatibility complex (MHC) genes for the complement proteins factor B, C2, C4A, and C4B] from 32 Black families residing in Boston and Washington, DC. Twenty-five different complotypes were identified, among which there were four complotypes that had not been previously observed in our large database of complotypes compiled from family studies of Boston Caucasians and that are, presumably, unique to individuals of African origin. These four African-derived complotypes are FC(1,90)0, FC63, S1C2, 17, and SC(3,2,90)0. The frequencies of two of these four unique Black complotypes, FC(1,90)0 and FC63, were increased significantly when compared to Caucasians (pcorr less than 0.00042, pcorr = 0.00294, respectively). The complotype FC(1,90)0 was in positive linkage disequilibrium with HLA-DR3 haplotypes containing the B locus antigens Bw42, Bw52, Bw53, and Bw58, while FC63 was associated with HLA-Bw70, -DR5. These findings demonstrate the extensive polymorphism of complotypes in Blacks, and also suggest that it may be possible to define unique extended haplotypes of African origin.

A method for subtyping group-specific component in bloodstains

A method is described for subtyping group-specific component (Gc) derived from human bloodstains. Bloodstained cuttings were extracted in 6 M urea. The extracts were subjected to ultrathin-layer polyacrylamide gel isoelectric focusing in the pH 4.5-5.4 range. After isoelectric focusing, Gc was detected by immunofixation in cellulose acetate membranes. This method permitted the successful typing of Gc in at least four-month-old bloodstains maintained at room temperature. Bloodstains from 266 liquid blood samples of known origin were subjected to both this method and immunofixation conventional agarose gel electrophoresis with no phenotypic discrepancies observed. The Gc population data for Whites from Baltimore, Maryland, were homogeneous with white sample populations from other geographical locations within the U.S.A.; while Gc data from northern U.S.A. black sample populations appeared to be heterogeneous compared with a southern United States black sample population.

Genetic predisposition to acute lymphocytic leukemia in American blacks. A Pediatric Oncology Group study

Recent reports have shown an association between genes lying within the major histocompatibility complex (MHC), particularly HLA and factor B (Bf), and acute lymphocytic leukemia (ALL) in white children. The frequencies of Bf and complement component C4 phenotypes in 90 black American children with ALL were examined to determine if a genetic association existed. The Bf and C4 results for the black children with ALL were compared with frequencies in healthy black Americans from the same geographic region. The BfF allele was carried by 95.6% of the black ALL patients compared with 86.1% of the controls (P = 0.017; relative risk = 3.5). In contrast, only 2.2% of the patients with ALL were homozygous for BfS compared with 9.8% of the controls (P = 0.043; relative risk = 0.2). These findings are similar to those observed in white American children. The C4A6 phenotype was found in 11.9% of the black children with ALL compared with 0.6% of the controls (P = 0.0026; relative risk = 22.7). These findings represent the first reported association of a particular allele whose gene lies within the MHC with ALL in black American children. The results suggest that the occurrence of ALL in black American children may be partially due to a genetic influence.

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).