Duffy Antigen System - Population Genetics

Population Genetics

Differences in the racial distribution of the Duffy antigens were discovered in 1954, when it was found that the overwhelming majority of blacks had the erythrocyte phenotype Fy(a-b-): 68% in African Americans and 88-100% in African blacks (including more than 90% of West African blacks). This phenotype is exceedingly rare in whites. Because the Duffy antigen is uncommon in those of Black African descent, the presence of this antigen has been used to detect genetic admixture. In a sample of unrelated African Americans (n = 235), Afro-Caribbeans (n = 90) and Colombians (n = 93), the frequency of the -46T (Duffy positive) allele was 21.7%, 12.2% and 74.7% respectively.

Overall the frequencies of Fya and Fyb antigens in Caucasians are 66% and 83% respectively, in Asians 99% and 18.5% respectively and in blacks 10% and 23% respectively. The frequency of Fy3 is 100% Caucasians, 99.9% Asians and 32% Blacks. Phenotype fequencies are:

• Fy(a+b+): 49% Caucasians, 1% Blacks, 9% Chinese
• Fy(a-b+): 34% Caucasians, 22% Blacks, <1% Chinese
• Fy(a+b-): 17% Caucasians, 9% Blacks, 91% Chinese

While a possible role in the protection of humans from malaria had been previously suggested, this was only confirmed clinically in 1976. Since then many surveys have been carried out to elucidate the prevalence of Duffy antigen alleles in different populations including:

• The mutation Ala100Thr (G -> A in the first codon position—base number 298) within the FY*B allele was thought to be purely a Caucasian genotype, but has since been described in Brazilians. However, the study's authors point out that the Brazilian population has arisen from intermarriage between Portuguese, Black Africans, and Indians, which accounts for the presence of this mutation in a few members of Brazil's non-Caucasian groups. Two of the three Afro-Brazilian test subjects that were found to have the mutation (out of a total of 25 Afro-Brazilians tested) were also related to one another, as one was a mother and the other her daughter.

• This antigen along with other blood group antigens was used to identify the Basque people as a genetically separate group. Its use in forensic science is under consideration.

• The Andaman and Nicobar Islands, now part of India, were originally inhabited by 14 aboriginal tribes. Several of these have gone extinct. One surviving tribe—the Jarawas—live in three jungle areas of South Andaman and one jungle area in Middle Andaman. The area is endemic for malaria. The causative species is Plasmodium falciparum: there is no evidence for the presence of Plasmodium vivax. Blood grouping revealed an absence of both Fy(a) and Fy(b) antigens in two areas and a low prevalence in two others.

• In the Yemenite Jews the frequency of the Fy allele is 0.5879 The frequency of this allelle varies from 0.1083 to 0.2191 among Jews from the Middle East, North Africa and Southern Europe. The incidence of Fya among Ashkenazi Jews is 0.44 and among the non-Ashkenazi Jews it is 0.33. The incidence of Fyb is higher in both groups with frequencies of 0.53 and 0.64 respectively.

• In the Chinese ethnic populations—the Han and the She people—the frequencies of Fya and Fyb alleles were 0.94 and 0.06 and 0.98 and 0.02 respectively.

• The frequency of the Fya allelle in most Asian populations is ~95%.

• In Grande Comore (also known as Ngazidja) the frequency of the Fy(a- b-) phenotype is 0.86.

• In a survey of 115 unrelated Tunisians using both serological and DNA based methods gave the following results: FY*X frequency 0.0174; FY*1 = 0.291 (expressed 0.260, silent 0.031); FY*2 = 0.709 (expressed 0.427; silent 0.282). FY*2 silent is the most common allele in West African blacks and the high prevalence in this sample was interpreted as historical admixture.

• The incidence of Fy(a+b-) in northern India among blood donors is 43.85%.

• In Nouakchott, Mauritania overall 27% of the population are Duffy-positive. 54% of Moors are Duffy antigen positive, while only 2% of black ethnic groups (mainly Poular, Soninke and Wolof) are Duffy positive.

• A map of the Duffy antigen distribution has been produced. The most prevalent allele globally is FY*A. Across sub-Saharan Africa the predominant allele is the silent FY*BES variant.

• In Iran the Fy (a-b-) phenotype was found in 3.4%.

There appears to have been a selective sweep in Africa which reduced the incidence of this antigen there. This sweep appears to have occurred between 6,500 and 97,200 years ago (95% confidence interval)

The distribution within India has been studied in some detail.