Implications of the Genetic Epidemiology of Globin Haplotypes Linked to the Sickle Cell Gene in Southern Iran

Human Biology, Dec 2006 by Rahimi, Zohreh, Merat, Ahmad, Gerard, Nathalie, Krishnamoorthy, Rajagopal, Nagel, Ronald L

The gene flow in this region of the Arab-Indian haplotype in present-day Iran can be traced to the Sassanian Empire (200-600 C.E.). The eastern limits of this empire included present-day Pakistan (Indus River) and Afghanistan (Daar et al. 2000). The southern limits of this Persian empire extended to the northern shores of the Arabian peninsula, including present-day Kuwait, Bahrain, Qatar, United Arab Emirates, and the northern portions of the Sultanate of Oman. The Arab-Indian haplotype linked to the sickle cell gene has been found in all the countries studied in this region.

It is likely that the influx of β^sup S^ genes linked to the Benin and Bantu haplotypes, of African origin, must have occurred during the Arab slave trade. The Arab slave trade brought slaves into the Middle East from Africa as house slaves and concubines, hence its bias toward females (3/1) over males (1/3). The Arab slave trade, based on Islamic law, followed the same tradition of slavery within Africa: The sons and daughters of slaves were emancipated and blended rapidly into the local society (Bernard 1990; Segal 2001). The Arab slave trade came to a halt when the British, French, and Italians obtained control of the Horn of Africa in the 19th century, depriving the slave traders of ports of embarkation to the Middle East.

Are the different haplotypes associated with the sickle cell gene ethnic group specific in southern Iran? In fact, we find similar frequencies of the ArabIndian and African haplotypes in both the sickle cell anemia patients from Fars (Farsi speakers and presumably Persian in origin) and Khuzestan (Arab in origin). It seems to be the same situation for other ethnic groups but with less certainty because of their low numbers.

We speculate that the individuals with African physical features found in enclaves in southern Iran came from this latter-day slave trade, and the process of ethnic assimilation did not take place to the extent that the previous influx of slaves had managed to complete. The slave trade was finally outlawed in Zanzibar in 1873 and the Great Slave Market was closed down.

Why do we find African haplotypes in the Iranian populations studied in individuals without African physical features? The custom of the Arab slave trade to emancipate the first descendants of slaves had a major consequence: significant admixture of individuals with some African ancestry into the mainstream population. In Iran this genetic admixture is bound to be not obvious, because the descendants of slaves (mostly women) frequently married members of the general Iranian population. Hence the phenotypic features (skin color, facial features, hair cross-section that defines the type of hair) tended to disappear with the high number of exogamous marriages. The fact that most of the African male slaves were eunuchs in this part of the world also helped with this dilution process (Bernard 1990; Segal 2001).

In contrast to the high prevalence of the Arab-Indian haplotype linked to the β^sup S^ gene in patients, the study of β^sup A^ haplotypes indicated that the Arab-Indian haplotype is less frequent (10.9%) among normal Iranians (Table 4). Our finding suggests that the β^sup S^ gene linked to the Arab-Indian haplotype might have originated elsewhere (Indus River valley) and then migrated to southern Iran under the stimuli of Aryan invasion (Nagel and Labie 1989). The Bantu A2 typical and atypical haplotypes were the most prevalent (43.5%). Because the 5' portion of the Bantu haplotype corresponds to haplotype I (Orkin et al. 1982), the high prevalence of the Bantu A2 haplotype in southern Iran could be due to this fact and the fact that haplotype I is the most prevalent haplotype (42.9%) among normal individuals from western Iran (Rahimi et al. 2006).