Genetic studies have emphasized the contrast between North African and sub-Saharan populations, but the particular affinities of the North African mtDNA pool to that of Europe, the Near East, and sub-Saharan Africa have not previously been investigated. We have analysed 268 mtDNA control-region sequences from various Northwest African populations including several Senegalese groups and compared these with the mtDNA database. We have identified a few mitochondrial motifs that are geographically specific and likely predate the distribution and diversification of modern language families in North and West Africa. A certain mtDNA motif (16172C, 16219G), previously found in Algerian Berbers at high frequency, is apparently omnipresent in Northwest Africa and may reflect regional continuity of more than 20,000 years. The majority of the maternal ancestors of the Berbers must have come from Europe and the Near East since the Neolithic. The Mauritanians and West-Saharans, in contrast, bear substantial though not dominant mtDNA affinity with sub-Saharans.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1469-1809.1998.6260531.x

Mitochondrial DNA analysis of northwest African populations reveals genetic exchanges with European, near-eastern, and sub-Saharan populations.

Summary Background Several genes have been implicated in the pathogenesis of Parkinson's disease (PD). The aim of this study was to define the clinical symptoms and age-associated cumulative incidence of the most frequent mutation associated with PD, LRRK2 Gly2019Ser. Methods 238 patients with sporadic PD and 371 unrelated control participants from the Arab–Berber population were screened at the Institut National de Neurologie, Tunis. Symptoms of PD were assessed using the Hoehn and Yahr scale, the unified Parkinson's disease rating scale, and the Epworth scale. Genotyping for LRRK2 6055G→A, which causes the Gly2019Ser mutation, was done in all participants, and the age-specific cumulative incidence of PD was calculated by Kaplan-Meier analysis. Findings 30% of patients with PD in this case-control sample were carriers of LRRK2 Gly2019Ser. The age of onset of symptoms and the clinical presentation of patients with LRRK2 Gly2019Ser were similar to those of patients with idiopathic PD. Carriers of LRRK2 Gly2019Ser were 22·6 times (95% CI 10·2–50·1) more likely to be affected by PD than non-carriers. Tremor was the predominant symptom in LRRK2 Gly2019Ser carriers (92% [homozygotes] vs 75% [heterozygotes] vs 69% [non-carriers]; Cochran–Armitage trend test p=0·0587). Disease severity, response to treatment, and disease duration were similar among LRRK2 Gly2019Ser homozygotes, heterozygotes, and non-carriers (p=0·85). Disease penetrance in LRRK2 Gly2019Ser carriers ranged from less than 20% in those younger than 50 years to greater than 80% at 70 years. Interpretation The LRRK2 Gly2019Ser mutation in patients with PD is a useful aid to diagnosis. LRRK2 Gly2019Ser penetrance can vary but in most carriers PD seems an inevitable consequence of ageing. LRRK2 Gly2019Ser considerably increases susceptibility to neuronal degeneration, although the process might be mediated by many triggers. By contrast, idiopathic PD is rare before 50 years and the prevalence only increases to 4% in the oldest members of the population. Funding GlaxoSmithKline; National Institutes of Health; and Mayo Foundation.

https://www.thelancet.com/pdfs/journals/laneur/PIIS1474-4422(08)70116-9.pdf

LRRK2 Gly2019Ser penetrance in Arab–Berber patients from Tunisia: a case-control genetic study

Summary Berbers live in groups scattered across North Africa whose origins and genetic relationships with their neighbours are not well established. The first hypervariable segment of the mitochondrial DNA (mtDNA) control region was sequenced in a total of 155 individuals from three Tunisian Berber groups and compared to other North Africans. The mtDNA lineages found belong to a common set of mtDNA haplogroups already described in North Africa. Besides the autochthonous North African U6 haplogroup, a group of L3 lineages characterized by the transition at position 16041 seems to be restricted to North Africans, suggesting that an expansion of this group of lineages took place around 10500 years ago in North Africa, and spread to neighbouring populations. Principal components and the coordinate analyses show that some Berber groups (the Tuareg, the Mozabite, and the Chenini-Douiret) are outliers within the North African genetic landscape. This outlier position is consistent with an isolation process followed by genetic drift in haplotype frequencies, and with the high heterogeneity displayed by Berbers compared to Arab samples as shown in the AMOVA. Despite this Berber heterogeneity, no significant differences were found between Berber and Arab samples, suggesting that the Arabization was mainly a cultural process rather than a demographic replacement.

Mitochondrial DNA Heterogeneity in Tunisian Berbers

Parkinson's disease (PD) is a common neurodegenerative disorder, for which environmental and/or genetic factors are postulated as possible causes. Over the past decade there has been a substantial increase in the knowledge of the genetics of PD. Mutations in Leucine-rich repeat kinase 2 (LRRK2) are the most frequent genetic causes of PD, and the common G2019S mutation has been identified in various ethnic groups with variable frequency. The aim of this article is to review the literature relating to LRRK2 G2019S in the North African population, which is composed of two main ethnic groups - the Berbers and the Arabs. The frequency of LRRK2 G2019S is 30-41% in familial PD and 30-39% in apparently sporadic PD in North Africa. Within healthy controls, Moroccan Berbers appear to have the highest carrier frequency at 3.3%. The majority of the available studies do not draw a clear distinction between the two ethnic groups, despite the distinct possibility that their ancestral origins are different. Further research looking at the respective prevalences of LRRK2 G2019S in Berbers and Arabs, and in different Arab populations, seems justified.

/pdf/lrrk2-g2019s-in-the-north-african-population-a-review-1ortbw8nqw.pdf

LRRK2 G2019S in the North African population: a review.

During successive historical periods, Tunisia has been a crossroads of multiple civilizations and their corresponding key population movements. The aim of this study was to provide genetic information relating to the mixed origin of the Tunisian population, and to analyze its genetic relationship with other North African and Mediterranean populations. A set of 16 Alu and 3 Alu/STR compound systems has been analyzed in 268 autochthonous Tunisians from the north-center and the south of the country. Our two sampled populations showed no significant differentiation from one another in any of the three Alu/STR compound systems, whereas the analysis of the 16 Alu markers revealed a significant genetic differentiation between them. A sub-Saharan component shown by the three Alu/STR combinations is more noticeable in our north-center sample than in that of the south. The presence of two Alu/STR combinations specific to North African ancestral populations also suggests that the ancient Berber component is relatively more substantial in the north and center regions than in the south. Our Tunisian samples cluster together with other Berber samples from Morocco and Algeria, underpinning the genetic similarity among North Africans regardless of their current linguistic status (Berber or Arabic).

/pdf/mixed-origin-of-the-current-tunisian-population-from-the-5ftsusffye.pdf

Mixed origin of the current Tunisian population from the analysis of Alu and Alu /STR compound systems

Blood samples from 120 Tunisian Berbers of Gallala village were typed for Gm and Km immunoglobulin allotypes, alpha-1-antitrypsin variants and ABO blood groups. The results were compared with those of

H. Chaâbani

Papers

Genetic Characterization and Origin of Tunisian Berbers