Inter- and extra-Indian admixture and genetic diversity in reunion island revealed by analysis of mitochondrial DNA.

Reunion Island is a French territory located in the western Indian Ocean. The genetic pattern of the Reunionese population has been shaped by contributions from highly contrasting regions of the world. Over the last 350 years, several migration waves and cultural and socio-economic factors have led to the emergence of six main ethnic groups in Reunion. India is one of the principal regions that contributed to the setting up of the Reunionese population. Diversity, demographic and admixture analyses were performed on mtDNA variation of the Reunionese of Indian ancestry, including the Malbar and Zarab ethnic groups, in order to question their history. Using a phylogeographical approach, we generated and analysed quantitative data on the contribution of the Indian parental populations. Furthermore, we showed that the settlement of Reunion Island by Indians did not involve a founder effect, except in the very beginning of the Reunionese settlement (at the end of the 17(th) century). The accuracy of our results was optimised by a re-evaluation of the classification of the Southern Asian mtDNA haplogroups. Finally, by comparing our results to a previous study dealing with the Reunionese population, we highlighted how ethno-historical data are critical for reconstructing the complex history of multiethnic populations.

Admixture and sexual bias in the population settlement of La Réunion Island (Indian Ocean).

La Réunion, one of the three Mascarene islands located in the Indian Ocean, remained devoid of inhabitants until it was first colonized by the French in the middle of the 17th century. The continuous flow of foreign-born slaves and immigrant workers from Africa, India, Southeast Asia, and China to work on coffee and sugar cane plantations led to the island becoming a melting pot of people of multiple ethnic origins. To establish the impact of the different incoming ethnic groups on the present Reunionese gene pool, we have sequenced both hypervariable regions I and II of the mitochondrial DNA molecule, the 9 bp COII/tRNA(Lys) deletion, and four SNPs located in the coding region in a total of 41 samples of the general population, and a further 18 STRs and 35 SNPs on the Y chromosome in 26 of these samples. Our results show that there was a strong sexual bias (asymmetrical gene flow) in the peopling of La Réunion, where admixture events were mainly between male settlers and females from the incoming slave groups. Most of the Y-chromosome gene pool is of European/Middle Eastern ancestry (85%), whereas the mtDNA gene pool is mainly of Indian and East Asian ancestry (70%). The absence of genetic diversity within these two major components of the mtDNA gene pool suggests these populations may have witnessed strong founder effects during the colonization process.

Comparison of TAP2 frequencies in type 1 diabetes patients and healthy controls from three ethnic groups indicates an African origin for the TAP2 G allele.

In order to determine the ethnic origin of the transporter associated with antigen processing 2 (TAP2) G allele, initially discovered by us in a group of type 1 diabetes (insulin-dependent diabetes mellitus) patients living on Reunion Island, HLA TAP2 typing was performed using the polymerase chain reaction-amplification refractory mutation system (PCR-ARMS) method in type 1 diabetes patients and unrelated healthy controls of three different ethnic groups (Caucasians, Indians and black Africans from Senegal and Mauritius). The comparison of TAP2 allele frequencies in controls showed significant racial (ethnic) differences. The TAP2*0101 and TAP2 C alleles were increased, respectively, in the Caucasian (50% in Caucasians vs. 40% in other groups) and Senegalese (27% in Senegalese vs. 10% in other groups) populations. In comparison with Caucasians, the TAP2*0201 variant was significantly increased in the Indian population and decreased in the Senegalese black population. In addition, the TAP2 G allele was observed in the two African populations studied but not in the Caucasian or Indian population. This observation is consistent with the view that this allele is restricted to populations of African origin. In addition, we have determined the large extended haplotype DQA1-DQB1-DRB1 associated with TAP2 G. We found that this allele is preferentially associated with the large conserved haplotype HLA DQA1*0501-DQB1*0201-DRB1*0301.