The Presence of FYA^null Alele of Duffy Blood Group System in Blood Donors and Individuals from a Malarial Endemic Region of Brazil.

BACKGROUND: Malaria is a virulent disease caused by the Plasmodium parasite. Innate resistance to malaria infections in humans is conferred by various blood group polymorphisms. The Duffy blood group system consists of Fy^a and Fy^b antigens which are encoded by codominant alleles FYA and FYB. Four phenotypes are defined: Fy(a+b+), Fy(a+b−), Fy(a−b+) and Fy(a−b−). Erythrocytes of Duffy-negative individuals are resistant to invasion by P. vivax. In Blacks the Fy(a−b−) phenotype is associated with a single point mutation (-33T-C) in the GATA-1 binding motif for the erythroid promoter of FYB.

STUDY DESIGN AND METHODS: We investigated the phenotypes and the genotypes of Duffy blood group system of 250 individuals living in a malarial endemic region (MER) in the state of Amazon (Brazil), and of 199 blood donors (BD) from a non-endemic region. The phenotyping was done by agglutination gel tests (DiaMed-Latino América) using anti-Fy^a and anti-Fy^b reagents. The molecular analysis for FYA, FYB, FYB^ES (GATA box mutation nt -33T-C), and FYB^Weak (mutations 265 C-T, and 298 G-A) alleles, were performed by PCR-RFLP. The PCR products were digested by Ban I for FYA and FYB identifications; by Sty I for GATA box mutation; Acy I and Mwo I for 265 C-T and 298 G-A mutations, respectively. Some samples that showed discrepancy between the phenotype and genotype results were examined by sequence analysis using the ABI PrismâBig Dyeä Terminator Cycle Sequencing Ready Reaction Kit” (Perkin Elmer), and the interpretation by the software ABI PRISMä 377 DNA Sequencer”, 3.3 version (Perkin Elmer).

RESULTS: We found that 34/250 (13.6%) of 250 persons living in the MER and 37/199 (18.6%) of BD had phenotype and genotype discrepant results [Fy(a+b−) FYA/FYB]. In addition, we found that 16/34 (47%) of people living in the MER, and 4/37 (10.8%) of BD did not present the -33T-C mutation, the 265 C-T, or the 298 G-A mutations. The sequence analysis of 2 samples from persons from MER indicated the presence of -33T-C mutation in the FYA allele in one individual (1 FYA/FYB and W/M; FYA/FYB and M/M). Additionally, we detected that 18/34 (53%) of people living in the MER, and 33/37 (89.2%) of BD presented the -33T-C mutation. The sequence analysis of 5 samples indicated the presence of -33T-C mutation in the FYA allele in 4 cases [2 persons from MER and 2 from BD (FYA/FYB e M/M)].

CONCLUSION: Recently the mutation responsible for erythrocyte Duffy antigen-negativity [Fy(a−b−)] was demonstrated in FYA allele in a malarial endemic region of Papua New Guinea. The present data demonstrated the presence of the FYA^null allele not only in persons living in a malarial endemic region but also in Brazilian blood donors from non-endemic areas. In contrast with that which happens with the FYB allele, our results indicated that the presence of the -33T-C mutation in the FYA allele does not abolish the expression of the Fy^a antigen in the erythrocyte.