Research Article: The genetic heterogeneity of Arab populations as inferred from HLA genes

Date Published: March 9, 2018

Publisher: Public Library of Science

Author(s): Abdelhafidh Hajjej, Wassim Y. Almawi, Antonio Arnaiz-Villena, Lasmar Hattab, Slama Hmida, Amr H Sawalha.

http://doi.org/10.1371/journal.pone.0192269

Abstract

This is the first genetic anthropology study on Arabs in MENA (Middle East and North Africa) region. The present meta-analysis included 100 populations from 36 Arab and non-Arab communities, comprising 16,006 individuals, and evaluates the genetic profile of Arabs using HLA class I (A, B) and class II (DRB1, DQB1) genes. A total of 56 Arab populations comprising 10,283 individuals were selected from several databases, and were compared with 44 Mediterranean, Asian, and sub-Saharan populations. The most frequent alleles in Arabs are A*01, A*02, B*35, B*51, DRB1*03:01, DRB1*07:01, DQB1*02:01, and DQB1*03:01, while DRB1*03:01-DQB1*02:01 and DRB1*07:01-DQB1*02:02 are the most frequent class II haplotypes. Dendrograms, correspondence analyses, genetic distances, and haplotype analysis indicate that Arabs could be stratified into four groups. The first consists of North Africans (Algerians, Tunisians, Moroccans, and Libyans), and the first Arabian Peninsula cluster (Saudis, Kuwaitis, and Yemenis), who appear to be related to Western Mediterraneans, including Iberians; this might be explained for a massive migration into these areas when Sahara underwent a relatively rapid desiccation, starting about 10,000 years BC. The second includes Levantine Arabs (Palestinians, Jordanians, Lebanese, and Syrians), along with Iraqi and Egyptians, who are related to Eastern Mediterraneans. The third comprises Sudanese and Comorians, who tend to cluster with Sub-Saharans. The fourth comprises the second Arabian Peninsula cluster, made up of Omanis, Emiratis, and Bahrainis. It is noteworthy that the two large minorities (Berbers and Kurds) are indigenous (autochthonous), and are not genetically different from “host” and neighboring populations. In conclusion, this study confirmed high genetic heterogeneity among present-day Arabs, and especially those of the Arabian Peninsula.

Partial Text

The human leukocyte antigens (HLA) system plays a key role in self-nonself recognition, and is divided into class I (HLA-A, -B, and -C) and class II (HLA-DP, -DQ, and -DR) loci, and comprises 220 genes in a 3.6 Mb region found on the short arm of chromosome 6. HLA system is highly polymorphic, and in excess of 17,000 alleles were detected. For example, there are 4,828 B, 3,968 A, and 3,579 C class I alleles, compared with 2,103 DRB1, and 1,142 DQB1 class II alleles. Several HLA alleles were associated with various auto-immune and infectious diseases [1]. HLA class I and class II loci are characterized by high (80–90%) heterozygosity, and thus constitute reliable genetic markers for phylogenetic study, and thus are useful for anthropological studies.

This meta-analysis is the first genetic anthropology study in MENA region, and included 100 populations from 36 Arab and neighbouring countries, and comprising in excess of 16,000 individuals. A main outcome of the study is the lack of striking differences in the distribution of HLA alleles and haplotypes between North Africans and Arabian Peninsula populations. On the contrary, key differences were noted between Levant Arabs (Lebanese, Palestinians, Syrians), and other Arab populations, highlighted by high frequencies of A*24, B*35, DRB1*11:01, DQB1*03:01, and DRB1*11:01-DQB1*03:01 haplotype in Levantine Arabs compared to other Arab populations. Class I haplotype frequencies are lower than Class II haplotypes, because of weak LD between A and B loci, due to long physical distance between them, compared to DRB1 and DQB1 loci. The identification of shared haplotypes between Arabs and other Mediterranean and Asian populations is attributed to the higher admixture of Mediterraneans and Asians in Arab populations.

This study supports the notion that Arabs are divided into four groups. The first consisting of North Africans (Algerians, Tunisians, Moroccans, and Libyans), Saudis, Kuwaitis, and Yemenis, with relatedness to Western Mediterraneans, including Iberians. The second includes Levantine Arabs (Palestinians, Jordanians, Lebanese, and Syrians), Iraqi, and Egyptians, who appear to be related to the Eastern Mediterranean and Iranians, who in turn belonged to ‘Great Levant’ historically described. The third consists of Sudanese and Comorians who associate with Sub-Saharan Africans. Finally, the fourth group of Arabs comprises Omanis, Emiratis, and Bahrainis. This group associates with heterogeneous populations (Mediterranean, Asian and sub-Saharan). Lastly, the two main indigenous minorities, Berbers and Kurds, are not genetically different from the ‘host’ and neighboring populations.

 

Source:

http://doi.org/10.1371/journal.pone.0192269

 

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