New insights into the genetic history of Tunisians: Data from Alu insertion and apolipoprotein E gene polymorphisms

Alu insertion polymorphisms in the African Sahel and the origin of Fulani pastoralists

BACKGROUND

The origin of Western African pastoralism, represented today by the Fulani nomads, has been a highly debated issue for the past decades, and has not yet been conclusively resolved.

AIM

This study focused on Alu polymorphisms in sedentary and nomadic populations across the African Sahel to investigate patterns of diversity that can complement the existing results and contribute to resolving issues concerning the origin of West African pastoralism.

SUBJECTS AND METHODS

A new dataset of 21 Alu biallelic markers covering a substantial part of the African Sahel has been analysed jointly with several published North African populations.

RESULTS

Interestingly, with regard to Alu variation, the relationship of Fulani pastoralists to North Africans is not as evident as was earlier revealed by studies of uniparental loci such as mtDNA and NRY. Alu insertions point rather to an affinity of Fulani pastoralists to Eastern Africans also leading a pastoral lifestyle.

CONCLUSIONS

It is suggested that contemporary Fulani pastoralists might be descendants of an ancestral Eastern African population that, while crossing the Sahara in the Holocene, admixed slightly with a population of Eurasian (as evidenced by uniparental polymorphisms) ancestry. It seems that, in the Fulani pastoralists, Alu elements reflect more ancient genetic relationships than do uniparental genetic systems.

Association between an angiotensin-converting enzyme gene polymorphism and Alzheimer's disease in a Tunisian population

BACKGROUND

The angiotensin-converting enzyme gene (ACE) insertion/deletion (I/D or indel) polymorphism has long been linked to Alzheimer's disease (AD), but the interpretation of established data remains controversial. The aim of this study was to determine whether the angiotensin-converting enzyme is associated with the risk of Alzheimer's disease in Tunisian patients.

METHODS

We analyzed the genotype and allele frequency distribution of the ACE I/D gene polymorphism in 60 Tunisian AD patients and 120 healthy controls.

RESULTS

There is a significantly increased risk of AD in carriers of the D/D genotype (51.67% in patients vs. 31.67% in controls; p = .008, OR = 2.32). The D allele was also more frequently found in patients compared with controls (71.67% vs. 56.25%; p = .003, OR = 2.0). Moreover, as assessed by the Mini-Mental State Examination, patient D/D carriers were more frequently found to score in the severe category of dementia (65%) as compared to the moderate category (32%) or mild category (3%).

CONCLUSIONS

The D/D genotype and D allele of the ACE I/D polymorphism were associated with an increased risk in the development of AD in a Tunisian population. Furthermore, at the time of patient evaluation (average age 75 years), patients suffering with severe dementia were found predominantly in D/D carriers and, conversely, the D/D genotype and D allele were more frequently found in AD patients with severe dementia. These preliminary exploratory results should be confirmed in larger studies and further work is required to explore and interpret possible alternative findings in diverse populations.

Spatial principal component analysis points at global genetic structure in the Western Mediterranean

Many studies have tackled the existence of a genetic barrier in the Strait of Gibraltar between Iberian and North African populations, often with controversial conclusions. Here, we address this issue using a collection of Western Mediterranean populations and two dimensionality reduction methods: principal component analysis (PCA) and spatial PCA (sPCA). Our four different data sets consisted of (i) 16 polymorphic Alu insertions in 12 populations; (ii) 35 single-nucleotide polymorphisms in 13 populations; (iii) 13 short tandem repeats in 11 populations; and (iv) all 64 markers in 9 populations. In all PCA plots, South European and North African samples were visually distinguishable along the first PC. Several smaller clusters were also identifiable, especially on the African side of our geographical setting. sPCA indicated a single global structure for each of the marker sets and no local structures. These results are more compatible with a clinal distribution of allele frequencies rather than with abrupt changes, suggesting that isolation-by-distance, rather than a barrier to gene flow, is a more likely mechanism of genetic differentiation in the Western Mediterranean. An alternative/complementary explanation is progressive introgression from North African to Southwestern European populations.

An investigation of the genetic diversity of the Kerkennah islands and Mahdia (Tunisia) using biparental markers

BACKGROUND

Kerkennah is one of the main inhabited islands of Tunisia. The origin of the population of Kerkennah has not been established and no well-defined ethnic groups have been identified nor are genetic studies available. Mahdia, a Tunisian coastal city, has a long history dating back to ancient times.

AIM

To discover the genetic diversity of the two studied populations and analyse their relationships with other Mediterranean populations.

SUBJECT AND METHODS

Seven human-specific Alu insertion polymorphisms were typed in 99 individuals born in Kerkennah and Mahdia.

RESULTS

A neighbour-joining tree and MDS multidimensional scaling analysis showed that these Tunisian populations are scattered amongst North African and Europeans populations, indicating their high genetic diversity and mosaic aspect. The important finding of this study was the proximity of Kerkennah to Moroccans. Hence, the actual gene pool of this insular population may descend from the ancestral population known to be of Moroccan origin. Concerning Mahdia, its closeness to Eurasian populations and some Tunisian groups reflected a high Eurasian genetic component for North African populations and confirmed their heterogeneity.

CONCLUSION

The strategic location of the two studied populations and their fortifications have allowed them to play a leading role in the Mediterranean basin.

Analysis of HLA-A, -B, -C, -DR, -DQ polymorphisms in the South Tunisian population and a comparison with other populations

BACKGROUND

The Human Leucocyte Antigen (HLA) system is often used as a genetic marker for analysing populations. HLA antigen distribution among the Tunisian population is not well defined because of the lack of a general population study.

AIM

The aim of the present study was to investigate the polymorphism of HLA-A, -B, -C, -DR and -DQ loci in the South Tunisian population.

SUBJECTS AND METHODS

This study has investigated HLA-A, -B, -C, -DR and -DQ polymorphisms in 123 unrelated healthy individuals originating from the south of Tunisia. HLA class I was studied by serology and completed by polymerase chain reaction-sequence specific primer (PCR-SSP). HLA class II was performed using PCR-SSP.

RESULTS

The most common alleles were A-2 (0.2154), B-44 (0.1179), C7 (0.2114), DR4 (0.1626) and DQ2 (0.313). A1-B-8-C7-DR3-DQ2 (2.84%) was the predominant haplotype in this population. Comparisons with data of other worldwide populations based on phylogenetic tree and multidimensional scaling analysis were done. This study suggests that both HLA class I and class II polymorphism specificities demonstrate a high diversity in this South Tunisian population, which reflects ancient and recent admixture with neighbouring populations.

CONCLUSION

The results provide useful information for further studies of Tunisian population evolution, anthropology and for resolving HLA frequencies when searching for HLA-compatible donors in transplantation and for the analysis of disease associations.

Founder mutations in Tunisia: implications for diagnosis in North Africa and Middle East

Background

Tunisia is a North African country of 10 million inhabitants. The native background population is Berber. However, throughout its history, Tunisia has been the site of invasions and migratory waves of allogenic populations and ethnic groups such as Phoenicians, Romans, Vandals, Arabs, Ottomans and French. Like neighbouring and Middle Eastern countries, the Tunisian population shows a relatively high rate of consanguinity and endogamy that favor expression of recessive genetic disorders at relatively high rates. Many factors could contribute to the recurrence of monogenic morbid trait expression. Among them, founder mutations that arise in one ancestral individual and diffuse through generations in isolated communities.

Method

We report here on founder mutations in the Tunisian population by a systematic review of all available data from PubMed, other sources of the scientific literature as well as unpublished data from our research laboratory.

Results

We identified two different classes of founder mutations. The first includes founder mutations so far reported only among Tunisians that are responsible for 30 genetic diseases. The second group represents founder haplotypes described in 51 inherited conditions that occur among Tunisians and are also shared with other North African and Middle Eastern countries. Several heavily disabilitating diseases are caused by recessive founder mutations. They include, among others, neuromuscular diseases such as congenital muscular dystrophy and spastic paraglegia and also severe genodermatoses such as dystrophic epidermolysis bullosa and xeroderma pigmentosa.

Conclusion

This report provides informations on founder mutations for 73 genetic diseases either specific to Tunisians or shared by other populations. Taking into account the relatively high number and frequency of genetic diseases in the region and the limited resources, screening for these founder mutations should provide a rapid and cost effective tool for molecular diagnosis. Indeed, our report should help designing appropriate measures for carrier screening, better evaluation of diseases burden and setting up of preventive measures at the regional level.

Genetic differentiation and origin of the Jordanian population: an analysis of Alu insertion polymorphisms

AIM

Although much of Jordan is covered by desert, its north-western region forms part of the Fertile Crescent region that had given a rich past to Jordanians. This past, scarcely described by historians, is not yet clarified by sufficient genetic data. Thus in this paper we aim to determine the genetic differentiation of the Jordanian population and to discuss its origin.

METHODS

A total of 150 unrelated healthy Jordanians were investigated for ten Alu insertion polymorphisms. Genetic relationships among populations were estimated by a principal component (PC) plot based on the analyses of the R-matrix software.

RESULTS

Statistical analysis showed that the Jordanian population is not significantly different from the United Arab Emirates population or the North Africans. This observation, well represented in PC plot, suggests a common origin of these populations belonging respectively to ancient Mesopotamia, Arabia, and North Africa.

CONCLUSION

Our results are compatible with ancient peoples' movements from Arabia to ancient Mesopotamia and North Africa as proposed by historians and supported by previous genetic results. The original genetic profile of the Jordanian population, very likely Arabian Semitic, has not been subject to significant change despite the succession of several civilizations.

Research of the origin of a particular Tunisian group using a physical marker and Alu insertion polymorphisms

The aim of this study was to show how, in some particular circumstances, a physical marker can be used along with molecular markers in the research of an ancient people movement. A set of five Alu insertions was analysed in 42 subjects from a particular Tunisian group (El Hamma) that has, unlike most of the Tunisian population, a very dark skin, similar to that of sub-Saharans, and in 114 Tunisian subjects (Gabes sample) from the same governorate, but outside the group. Our results showed that the El Hamma group is genetically midway between sub-Saharan populations and North Africans, whereas the Gabes sample is clustered among North Africans. In addition, The A25 Alu insertion, considered characteristic to sub-Saharan Africans, was present in the El Hamma group at a relatively high frequency. This frequency was similar to that found in sub-Saharans from Nigeria, but significantly different from those found in the Gabes sample and in other North African populations. Our molecular results, consistent with the skin color status, suggest a sub-Saharan origin of this particular Tunisian group.

Polymorphism FXII 46C>T and cardiovascular risk: additional data from Spanish and Tunisian patients

BACKGROUND

Previous studies showed an association between Coagulation Factor XII 46C>T polymorphism and variation in FXII plasma levels, as 46C>T seems to affect the translation efficiency. Case-control studies in Spanish samples indicated that genotype T/T is an independent risk factor for venous thrombosis, ischemic stroke and acute coronary artery disease. In this study, we tried to reaffirm the importance of 46C>T in two samples from Spain and Tunisia.

FINDINGS

A Transmission Disequilibrium Test (TDT) based on 101 family trios from Barcelona with one offspring affected by ischemic heart disease and a classical case-control study based on 76 patients with IHD and 118 healthy individuals from North and Centre-South Tunisia were conducted. Subjects were genotyped for 46C>T and data were analyzed accordingly, revealing no association in any of the two samples (TDT: P = 0.16, relative risk 1.17; case-control study: P = 0.59, odds ratio 1.36).

CONCLUSION

The results suggest that 46C>T is not a risk factor for ischemic heart disease in any of the two analyzed samples and therefore the polymorphism seems not to be a universal risk factor for cardiovascular diseases.

Apolipoprotein gene polymorphisms and plasma levels in healthy Tunisians and patients with coronary artery disease

Aim

To analyze apolipoprotein gene polymorphisms in the Tunisian population and to check the relation of these polymorphisms and homocysteine, lipid and apolipoprotein levels to the coronary artery disease (CAD).

Methods

In healthy blood donors and in patients with CAD complicated by myocardial infarction (MI) four apolipoprotein gene polymorphisms [APO (a) PNR, APO E, APO CI and APO CII] were determined and plasma levels of total homocysteine, total cholesterol (TC), triglycerides (TG), HDL-cholesterol (HLD-C) and apolipoproteins (apo A-I, Apo B, Apo E) were measured.

Results

Analysis of the four apolipoprotein gene polymorphisms shows a relative genetic homogeneity between Tunisian population and those on the other side of Mediterranean basin. Compared to controls, CAD patients have significantly higher main concentrations of TC, TG, LDL-C, apo B and homocysteine, and significantly lower ones of HDL-C, apo A-I and apo E. The four apolipoprotein gene polymorphisms have not showed any significant differences between patients and controls. However, the APO E4 allele appears to be associated to the severity of CAD and to high levels of atherogenic parameters and low level of apo E, which has very likely an anti-atherogenic role.

Conclusion

Although APO (a) PNR, APO CI and APO CII genes are analyzed in only few populations, they show a frequency distribution, which is not at variance with that of APO E gene and other widely studied genetic markers. In the Tunisian population the APO E 4 appears to be only indirectly involved in the severity of CAD. In the routine practice, in addition of classic parameters, it will be useful to measure the concentration of apo E and that of Homocysteine and if possible to determine the APO E gene polymorphism.