DNA analysis of Duffy genes in American blacks

Background: Because limited studies have shown that the Duffy genotype is not accurately reflected by the erythrocyte phenotype, we used PCR-RFLP to determine the true FY1 and FY2 gene frequencies in blacks. Methods: Genomic DNA was extracted from 81 randomly selected black individuals, amplified using PCR, digested with BanI and electrophoresed in 1.8% gels. Direct DNA sequencing of the FY regulatory region was done on a sample which had weak Fy(b) antigens. Standard serological techniques were used to type the erythrocytes for Fy(a) and Fy(b). Results: The most common genotype (83%) in blacks was Fy(a-b+) but almost all of the samples serologically typed as Fy(a-b-). The new gene frequencies are 0.08 for FY1 and 0.92 for FY2. Two donors whose erythrocytes typed weakly positive for Fy(b) and appeared to be Fy(x) were homozygous for FY2 by DNA testing. DNA sequencing of the regulatory region for Duffy found a mutation in an Spl binding site in the Fy(x) donor. Conclusions: We conclude that (1) the FY2 gene occurs in a much higher frequency in blacks than previously reported which may explain the lack of anti-Fy(b) in this ethnic group and (2) Fy(x) appears to be a the product of a mutant FY2 gene giving a quantitative variation in expression.