The investigation of the origin of Southern Tunisians using HLA genes

Abstract

The south of Tunisia is characterized by marked ethnic diversity, highlighted by the coexistence of native Berbers with Blacks, Jews and Arab-speaking populations. Despite this heterogeneity, genetic anthropology studies investigating the origin of current Southern Tunisians were rarely reported. We examined human leukocyte antigen (HLA) class I (A, B) and class II (DRB1, DQB1) gene profiles of 250 unrelated Southern Tunisians, and compared them with those of Arab-speaking communities, along with Mediterranean and sub-Sahara African populations using genetic distances, neighbor-joining dendrograms, correspondence and haplotype analysis. In total, 137 HLA alleles were detected, which comprised 32 HLA-A, 52 HLA-B, 32 DRB1 and 21 DQB1 alleles. The most frequent alleles were HLA-A*02:01(18.02%), HLA-B*50:01 (9.11%), HLA-DRB1*07:01 (22.06%) and HLA-DQB1*02:01 (17.21%). All pairs of HLA loci show significant linkage disequilibrium. The four loci depict negative F (the normalized deviate of the homozygosity) values indicating an overall trend to balancing selection. Southern Tunisians appear to be closely related to others Tunisian populations including Berbers, North Africans and Iberians. On the contrary, Southern Tunisians were distinct from Palestinian, Lebanese and Jordanian Middle Eastern Arab-speaking population, despite the deep Arab incursions and Arabization that affected Southern Tunisia. In addition, Southern Tunisians were distant from many sub-Saharan communities, evidenced by genetic distance analysis. Collectively, this indicates a limited genetic contribution of Arab invasion and Black caravans on the makeup of Southern Tunisian gene pool.

The genetic heterogeneity of Arab populations as inferred from HLA genes

“…Using genetic distances, correspondence analysis and NJ trees, we showed earlier [ 61 , 62 ] and in this study that Palestinians, Syrians, Lebanese and Jordanians are closely related to each other and to Eastern Mediterranean Europeans (Turks, Cretans, Greeks), Egyptians and Iranians, and confirmed by HLA class I ( A , B ) and class II markers ( DRB1 and DQB1 ) analysis. However, Levant Arabs are distant from North African Arabs (Tunisians, Algerians, Moroccans and Libyans) and Iberians (Basques, Spaniards).…”

“…The relatedness between North Africans and Iberians was previously discussed [ 29 , 59 – 62 , 69 , 78 , 79 , 86 , 88 ]. Using correspondence analysis, NJ trees and genetic distances, our results show that North Africans are genetically close to Iberians, which is supported by historical events.…”

Association of HLA Class II Alleles and Haplotypes with Type 1 Diabetes in Tunisian Arabs

“…DRB1 * 08, * 09, * 12, * 14, * 16, and DQB1 * 04 were found to be rare in the sample of Tunisian population tested. It is noteworthy that this allelic distribution in controls was comparable to those previously described in healthy Tunisian population [31][32][33].…”

Genetics and genomic medicine in Tunisia

“…This resulted in a low admixture between them and the Arab tribes. This fact was further confirmed by the HLA typing data that demonstrated the low contribution of Arabs to the southern genetic pool (Hajjej et al., ).…”

“…DRB1*07:01-DQB1*02:02 was found to be the most frequent haplotype in Southern Tunisians (18.02%). This haplotype was also present in Tunisian Berbers (16.03%) (Hajjej, Almawi, Hattab, El-Gaaied, & Hmida, 2016). In fact, the HLA class II allele DRB1*07:01 was present at 22.06% in the southern population, and was detected at high frequencies in Tunisian Berbers (17.6%) and in Ghannouchians (28.7%) occupying a village situated at the eastern south of Tunisia and characterized by high endogamy, behaving like an isolate .…”