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The genetic heterogeneity of Arab populations as inferred from HLA genes
The genetic heterogeneity of Arab populations as inferred from HLA genes
PLoS One. 2018; 13(3): e0192269.
Published online 2018 Mar 9. doi: 10.1371/journal.pone.0192269
PMCID: PMC5844529
PMID: 29522542
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.
Subsequent spread of Islam involved swift invasion of Persia (637-651AD), Iraq, Levant, and Egypt (639 AD), which extended into North Africa (640–709), and to Spain, Portugal, and France (Poitiers) in 8th century AD. Eastwards, Arab expansion to Central Asia, Bukhara (Uzbekistan), Afghanistan (637–709), and the Indus border (664–712) followed. Northwards, Arab invaders were in contact with the Byzantine Empire, and the Caspian and Caucasus to the north [15, 16]. With the Islamic expansion from 7th century, social and political groups were gradually Arabized. The spreading of Arab-Muslim culture was at the expense of local languages (as Berber, Kurdish), especially in Middle East and North Africa, resulting in the Arabized population speaking variants of Arabic, mixed with original languages (dialect). The extent of gene Arab exchange with these autochthonous groups is undetermined but is thought to be lower than religious/cultural influence.
Results of HLA-B locus are presented in Table 3. B*35 was the most frequent B* allele in Palestinians (20.3%) [29] and Lebanese-Armenians (19.8%) [27]. B*35 was found at varied frequencies in Iraqi Kurds (15.6%) [23], Omanis (15.3%) [30], Jordanians (14.9%) [31], and Arab Emirati (11.1%) [23] populations. B*51 was the second most frequent allele, and high frequencies were recorded for Saudis (19.3%) [23], Omanis (17.5%) [30], and Arab Emirati (15.6%) [23] populations. B*50 was also a frequent B* allele in most Arabs, including Saudis (18.8%) [23], and Libyans (16.1%) [31], along with B*08, and B*44 among the Tunisian Berbers of Zrawa (32.8%) [24], the latter being the highest frequency worldwide. Similarly, the frequency of B*27 is the highest among Jordanians (27.1%) [31]. In contrast, B*37, *42, *46, *47, *48, *54, *59, *67, and *78 alleles are extremely rare or virtually in all Arab populations.
The most common DRB1 and DQB1 alleles among Arabs are shown in Table 4. DRB1*07:01 was the most frequent allele among Tunisians from Ghannouch (28.6%) [33], Jordanians (26.9%) [31], and Saudis (26.6%) [23], while Egyptians (8.3%) and Sudanese had the lowest frequencies of DRB1*07:01. DRB1*03:01 was the second most frequent DRB1* allele in some Arabs, such as Tunisians of Tunis (21.9%) [34] and Moroccans of Metelsa (20.2%) [23], but rare in Jordanians (2.4%) [31]. DRB1*11:01 was also frequent among some Arabs, such as Lebanese (36.8%) [35], but rare among Saudis (4.8%) and Moroccans of Chayoua (2.5%) [23]. Furthermore, DRB1*13:01, *13:02, and *15:01 alleles are relatively frequent among Arabs. High frequency of DRB1*13:01 were recorded for Sudanese (23.3%), while DRB1*13:02 was virtually absent in Bahraini [35] and Sudanese [23]. All DRB1*09, *12, and *14 subtypes are extremely rare among Arabs. In addition, DRB1*16 subtypes are rare in all Arab populations except for Bahrain, where DRB1*16:01 is found at a high frequency (13.9%) [35].Haut du formulaire.
Comparison at the generic level was made using genetic distances based on DRB1* and DQB1* allelic frequencies. Four groups can be interpreted from Fig 3. The first group comprises North African Arabs (Tunisians, Algerians, Moroccans, Libyans), Western Mediterranean Europeans (Iberians, French), Arabian Peninsula Arabs (Saudis, Kuwaitis, Yemenis), and Arab minority of Iran (Khuzestani). The second group is formed by Eastern Mediterranean Europeans (Greeks, Cretans, Albanians, Turks, Macedonians), Italians, Levant Arabs (Palestinians, Lebanese, Syrians), Iraqi-Kurds, Tunisian Berbers (Djerba), and Iranians. The third group comprises Sub-Saharan Africans (Fulani, Mossi, Rimaibe, Bubi, Mandenka, and Senegalese). Omanis, Bahrainis, Egyptians, and Sudanese form a heterogeneous group containing Asians and Sub-Saharan Africans. Similar results but with notable differences, were observed in dendrograms built with standards genetic distances (SGD) based on generic DRB1(S1 Fig) and generic B loci (S2 Fig).
High-resolution DRB1 correspondence analysis (Fig 4) demonstrated the clustering of the studied populations into three groups. The first containing North Africans (Tunisians, Algerians, Moroccans, and Libyans), Iberians (Basques, Spaniards, Portuguese, Murcians), French, Saudis, Yeminis-Jews, and Khuzestani Arabs. The second contains Eastern Mediterraneans (Greeks, Cretans, Lebanese, Palestinians, and Macedonians), Berbers of Djerba, Italians, Iraqi-Kurds, Iranians, Egyptians, Ashkenazi-Jews, and Moroccan-Jews. The last cluster consists of Sub-Saharan populations. It should be noted that Jordanians, Bahrainis, and Sudanese were outside these main groups. Similarly, correspondence analysis using class I (A and B) identified three main clusters (Fig 5). The first cluster contained all Sub-Saharan Africans along with Sudanese. The second cluster contains Eastern Mediterranean populations (Albanians, Greeks, Cretans, Lebanese, Palestinians, and Macedonians), Italians, Iraqi-Kurds, Ashkenazi-Jews, and Jordanians-A. The last cluster includes North Africans (Tunisians, Algerians, Moroccans, and Libyans), Iberians (Basques, Spaniards), French, and Saudis.
Correspondence analysis based on generic DRB1 data, and using only Arab populations shows that Arabs can cluster into four groups (Fig 6). The first contains the North Africans (Tunisians, Algerians, Moroccans, and Libyans), Saudis, Yemenis, Kuwaitis, and Khuzestanis (Iranian Arabs). The second cluster includes the Arabs of Levant (Palestinians, Jordanians, Lebanese, Syrians), Egyptians, Iraqi Kurds, and Moroccans Jews. The third group consists of Bahrainis, Omanis, Emiratis and Famoori (Iranian Arab). The fourth is composed of Sudanese, Sudanese from Nuba, and Comorians.
Syrians are genetically close to Eastern Mediterranean, as Cretans (-0.0001) and Lebanese Armenians (0.0050), while Tunisians are closed to Western Mediterraneans as North Africans and Iberians, and Saudis. The populations most related to Tunisians are the other Tunisian populations (Gabesians, -0.0139), Moroccans (Agadir; -0.0080), and Algerians (-0.0055). Sub-Saharans such as Congolese (0.0519) and Nigerians (0.0828), and Greeks (0.0836) showed the closest genetic distances to Comorians. It is noteworthy that Arab minority in Khuzestan (Iran) displayed close relatedness with North Africans [as Gabesians from Tunisia (-0.0086) and Orans from Algeria], and Saudis (0.0231).
Iberians, North Africans, and Arabian Peninsula inhabitants
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. First, this relatedness is attributed to the Berber migration from the African Sahara northwards in 10000–4000 BC, because of hyper-arid conditions [69]. It may also be explained by the similar history between Iberians and North Africans, both of whom were invaded by Phoenicians, Romans, Germans, Muslim Arabs [89]; the respective invading armies had a mixed genetic complexity; indeed, most of them were mercenaries recruited in recent conquests like in the case of Phoenicians [90] and Muslim who invaded Iberia had troops that were mostly Berbers. The invasion of Iberia by Muslims in the 8th century AD may have had a role in the relatedness between North Africans and Iberians for two reasons: first, most Muslim invaders recruits were North African Berbers, and the second is explained by the 8 centuries period of settlement of the Muslims in Iberia, although more ancient and continuous gene exchange since prehistoric times between Iberia and North Africa may have been induced the main exchange [86]; massive mixed marriages and breeding across religious Iberian groups under Muslim rule is not documented.
The analyses performed showed that current North Africans are closely related to Tunisian (Zrawa and Matmata) and Moroccan (Sousse-Agadir and Eljadida) Berbers, suggesting that North Africans have a genetic Berber profile. On the contrary, North Africans displayed a greater distance from the Arabs of Levant (Palestinians, Syrians, Lebanese, and Jordanians), indicating low genetic contribution of Phoenician and Levant Arab invasion of North Africa. These observations based on HLA markers prompted the conclusion that all Berbers of North Africa constitute a homogeneous genetic unit, except for small isolates, such as the Berbers of Djerba, who display a Berber genetic profile.
Saudi populations used in this study originated from Eastern Saudi Arabia, especially from Riyadh province. There is no reliable HLA data on Eastern Saudi Arabia that shed light on pre-Islamic history; some ancient people may have originated from old Persians, but quantification is difficult and undetermined [91]. The genetic heterogeneity between Eastern and Western Saudi Arabia is very possible, and should be taken into account in further interpretation. All analyses performed here, using HLA-A,-B, -DRB1, and DQB1 markers support the notion that Saudis along with the Kuwaitis and Yemenis are closely related to North Africans.
The most plausible explanation for West Arabia and Yemen clustering with Iberian/North Africans is a possible important massive migration that occurred when Sahara underwent desiccation in all directions [92, 93]. Cultural and language relatedness of many Mediterranean languages, including old Iberian and Basque [92], with Berber language are concordant with our genetic findings and Saharan origin hypothesis; also a part of Arabian Peninsula inhabitants (including Yemen) may had been reached by Saharan people. In fact, Malika Hachid who has been studying Saharan and North African Archaeology, culture and rock painting/writing of prehistoric Sahara, even suggests that first known writing alphabet was originated in Sahara. Proto-Berber writing rock characters have been used (very similar to present day used Berber scripts). This Proto-Berber language could have appeared 5,000 years BC [94, 95].
Explanation to HLA Kuwait genetic similarity to this group seems more difficult to achieve but interaction between Arabian Peninsula and Mesopotamia through this strategic Kuwait area is documented since 6,500 years BC (Ubard Period) [96].
Arabs of Levant
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 strong relatedness between Levant Arab populations is explained by their common ancestry, the ancient Canaanites, who came either from Africa or Arabian Peninsula via Egypt in 3300 BC [97], and settled in Levant lowlands after collapse of Ghassulian civilization in 3800–3350 BC [98]. The relatedness is also attributed to the close geographical proximity, which constituted one territory before 19th century British and French colonization.
The close relatedness of Levant Arabs to Egyptians, as confirmed genetic distances using HLA markers, may be due to three reasons. First, Egypt is a neighbor to Levant Arab countries, and historically part of the Levant. Second, the Egyptians invaded the Levant several times throughout history; the most significant was 1468 BC invasion, where they settled for 12 centuries [99]. Third, the Canaanites, the likely ancestors of Levant Arabs, may have originated from Africa through Egypt, where they settled for a long period, suggesting likely admixture between Canaanites and Egyptians.
Historically, Levant is a wider region that included countries along the Eastern Mediterranean with its islands, and extended from Greece to Cyrenaica [100]. Broadly, Levant was historically characterized by high migratory flow between its sub-regions in all directions. For example, present-day Levant comprising Palestine, Lebanon, Syria, and Jordan has undergone successive invasions by populations originating from the great Levant, including Egyptians (1468 BC), Horites, Amorites, Hitites (Turks), Greeks (1200 BC), Assyrians (1090 BC) [99], and more recently the Ottomans. This has favored admixture, reduced distances and homogenized Great Levant populations, thus explaining the close relatedness of Levant Arabs to Eastern Mediterranean populations. On the other hand, Levant Arabs are distant from Saudis, Kuwaitis, and Yeminis, an indication that the contribution of the Arabian Peninsula populations to Levantine gene pool is low, probably due to the absence of the demographic aspect of 7th century invasion.
Clustering and genetic distances analyses demonstrated that Iraqi and Iranian Kurds are not genetically different from Iranians or neighboring populations, including Levant Arab, and are close to Turks and other Eastern Mediterranean populations. This suggests that Kurds originate from the region, and are in genetic harmony with neighboring populations, despite the clear cultural differences. This suggests that Kurds, Syrians, Jordanians, Palestinians, Iraqis, Lebanese, and Iranians probably share the same genetic profile, with few differences. Accordingly, our findings confirm the results of an earlier study of Arnaiz-Villena on Iraqi Kurds [54].
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.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5844529/
So..what's your opinion or analysis on that?
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Originally Posted by Sikeliot
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