ETHNIC VARIATION IN FREQUENCY OF AN ALLELIC POLYMORPHISM OF HUMAN FC-GAMMA-RIIA DETERMINED WITH ALLELE-SPECIFIC OLIGONUCLEOTIDE PROBES

We have genotyped 53 individuals from three ethnic groups (Japanese, C hinese, Asian Indian) for an allotypic polymorphism of a widely expres sed low affinity Fc receptor for IgG (Fc gamma RIIA). The method, requ iring PCR amplification of genomic DNA and Southern analysis with alle le specific oligonucleotide probes, detects a single nucleotide differ ence (G or A) at base 494 which results in an arginine (R) or histidin e (H) at amino acid 131 of the Fc gamma RIIA protein. This polymorphis m has been shown to determine the affinity of the receptor for hIgG2; Fc gamma RIIA-H131 has a high affinity for hIgG2 while Fc gamma RIIA-R 131 binds hIgG2 weakly. We found that the Japanese and Chinese groups have an increased frequency of the H/H131 allotype (61 and 50% respect ively) as compared to the Caucasian group (23%), in agreement with pre viously reported phenotype data. The genotype distribution of the Asia n Indian group was not different from our Caucasian group. The shifts in frequency of the R131 and H131 alleles in different populations may have implications for disease susceptibility when the hIgG2 antibody isotype predominates.