Allelic polymorphisms of human fcgamma receptor IIa and Fcgamma receptor IIIb among distinct groups in Brazil.

BACKGROUND

The FcgammaRIIA gene is expressed in two polymorphic forms, R131 and H131, which differ by the replacement of histidine by arginine at position 131. The FCGR3B (FcgammaRIIIB) gene exists in two allelic isoforms, known as FCGR3B1 (FcgammaRIIIB-NA1) and FCGR3B2 (FcgammaRIIIB-NA2), which differ in nucleotides 141, 147, 227, 277, and 349. An additional polymorphism is the SH antigen that is associated with the FCGR3B3 (FcgammaRIIIB-SH) allele.

STUDY DESIGN AND

METHODS

By use of a PCR with allele-specific primers, the allelic polymorphisms of FcgammaRIIA and FcgammaRIIIB were determined among 263 unrelated Brazilian subjects, including Amazon Indians (n = 92), blood donors (n = 85), and patients with sickle cell disease (SCD) (n = 86).

RESULTS

Amazon Indians had a significantly higher frequency of the R131 allele than did blood donors and SCD patients (0.91 vs. 0.55 vs. 0.55; p<0.001). NA1 and NA2 gene frequencies were found to be 0.67 and 0.21 for Amazon Indians, 0.58 and 0.42 for blood donors, and 0.61 and 0.39 for SCD patients, respectively. The FcgammaRIIIB-SH allele was absent from the Amazon Indians, but 9 (10.6%) blood donors and 10 (11.6%) SCD patients expressed this allele.

CONCLUSION

Overall, the data indicate that the distribution of the FcgammaRIIIB alleles is significantly different in Amazon Indians from the distribution in Brazilian blood donors or African Brazilian patients with SCD, but that it is similar to the distributions reported in Asian populations. Moreover, the distribution of the FcgammaRIIA and FcgammaRIIIB alleles among Brazilian blood donors and SCD patients is comparable to the distributions reported in whites from the United States and Europe.