Biomedical subjects

A Sanchez-Mazas

Publications and source records attributed to A Sanchez-Mazas.

31 records · Page 2Linked to original sources

PubMed1994

HLA-DRB1, DQA1 and DQB1 DNA polymorphisms in healthy Algerian and genetic relationships with other populations.

This study presents the results of HLA-DRB1, -DQA1, and -DQB1 sequence-specific oligonucleotide probe (SSOP) typings for a population sample of 47 individuals originating from Western Algeria. Allele and haplotype frequencies, as well as linkage disequilibria are computed by the standard methods used for the XIth International Histocompatibility Workshop data. A total of 24 alleles are detected at the DRB1 locus, where a very high heterozygosity level (0.914) is found. The highest DRB1 frequencies are 0.160, DRB1*1101, and 0.138, for DRB1*0301 and DRB1*0701. The DQA1 and DQB1 loci are less polymorphic. Among the 8 DQA1 alleles detected, DQA1*0501 is highly predominant with a frequency of 0.383. Thirteen DQB1 alleles are observed among which DQB1*0301 and DQB1*0201 are the most frequent (0.351 and 0.245, respectively). Three haplotypes predominate clearly: DRB1*1101-DQA1*0501-DQB1*0301 (0.138), DRB1*0701-DQA1*0201-DQB1*0201 (0.128) and DRB1*0301-DQA1*0501-DQB1*0201 (0.117). The two latter are among the most frequent haplotypes found in European and North American Caucasoid populations, but the DQA1*0501-DQB1*0201 association is not significant in Algerians. The genetic distances computed for each locus among a set of populations from different continents are significantly correlated to geography. They indicate that the Algerians are very close to South European populations, particularly to Sardinians, Italians, Romanians and French, with some intermediate characteristics between Europeans and sub-Saharan Africans. These results may serve as reference for future studies of HLA and disease in the Algerian population.

Adult↗

PubMed1994

HLA-DPB1 DNA polymorphism in the Swiss population: linkage disequilibrium with other HLA loci and population genetic affinities.

Allelic diversity at the HLA-DPB1 locus was determined by PCR-oligotyping in a sample of 125 healthy Swiss individuals. A total of 17 alleles were detected among which four main alleles (DPB1*0401, *0201, *0301, *0402) reached a cumulative frequency of 74.8%. HLA-A and -B (by serology) and HLA-DRB1 (by oligotyping) allelic polymorphisms were analysed also. HLA-B and HLA-DRB1 loci were highly polymorphic with 25 and 28 alleles respectively and similar heterozygosity levels of 0.93 and 0.92. These two loci were found to be more polymorphic than expected under neutrality, while lower heterozygosity levels were found for HLA-A (0.87) and DPB1 (0.81) loci. This paper presents also a global comparison of DPB1 allelic frequencies among 15 populations from four continents. As opposed to the DRB1 locus, overall DPB1 is shown to have a lower level of polymorphism and may be considered as neutral in all tested populations. DPB1 genetic diversity is correlated significantly with geography also, as found previously for DRB1. Two- and four-locus haplotype frequencies were determined and the significance of their linkage disequilibrium tested by an original non-parametric method. A significant positive linkage disequilibrium was found for 11 A-B, 16 B-DRB1, 7 DRB1-DPB1 and 3 A-B-DRB1-DPB1 haplotypes. The overall linkage disequilibrium between DRB1 and DPB1 was much lower than expected from the physical distance and lower than for A-B and B-DRB1 pairs. The implications of these results for bone marrow transplantation and for the evolution of HLA loci are discussed.

Alleles↗

PubMed1994

Rhesus polymorphism in New Caledonia. I. Genetic structures of three local populations.

Rhesus phenotypes are presented for a total of 2,052 individuals belonging to three sympatric populations of New Caledonia: Kanaks (Melanesians), Wallisians (Polynesians) and Europeans born in New Caledonia. The maximum-likelihood gene frequency estimations reveal a significant deviation from Hardy-Weinberg equilibrium for the Kanak and Wallisian samples. As suggested on statistical grounds, this disequilibrium can be attributed to antigene mistypings, frequently encountered for this system. This hypothesis leads to new estimations of Rhesus haplotype frequencies for the two samples. They reveal a high degree of genetic similarity (89.6%) between Kanaks and Wallisians, with little or no evidence of admixture with Europeans from New Caledonia. The latter are genetically close to southern Europeans in having a very high R1 frequency.

Adolescent↗

PubMed1994

Rhesus polymorphism in New Caledonia. II. Genetic comparison with other Oceanians.

Rhesus haplotype frequencies computed for 804 and 546 Wallisians from New Caledonia are compared to the data collected for 13 Oceanian samples belonging to the same Austronesian linguistic family. Genetic distances are computed between the 15 populations and used for a principal coordinate analysis. Kanaks are genetically close to Fidjians, while the Wallisian sample share a high genetic similarity with the Tonga islanders. The results obtained for the whole area including the Wallis homeland for the Wallisian sample indicate a tight relationship between geographical and genetic differentiations in the Pacific, supported by a high correlation coefficient between the two distance matrices. However, the observed patterns are better explained by the history of migrations reconstructed from archaeological and linguistic data than by a pure isolation-by-distance model.

Black People↗

PubMed1994

New data for AG haplotype frequencies in Caucasoid populations and selective neutrality of the AG polymorphism.

We present the results of AG antigen typings of three Caucasoid population samples: Lebanese, Tunisians, and Finns. AG haplotype frequencies estimated by maximum-likelihood methods are compared with the frequencies observed in 13 world populations previously tested for AG specificities by computing a genetic distance matrix used in a multivariate analysis. A high degree of polymorphism characterizes the three samples, with 10 haplotypes detected in the Lebanese and 11 haplotypes detected in the Tunisians and Finns; high heterozygosity levels are also present in the three populations. The genetic distance analysis shows that the three populations possess a genetic structure intermediate between those observed in sub-Saharan Africans and in Caucasoids from the Near East and India. This tight correspondence between AG differentiation and geography is confirmed by a highly significant correlation coefficient found between genetic and geographic distances computed worldwide, suggesting that an isolation by distance model of evolution applies to the AG system. The Ewens-Watterson test for selective neutrality on all world populations tested for AG specificities also supports the hypothesis that the AG system behaves like a neutral polymorphism. Overall, the AG differentiation pattern appears to be close to the patterns observed for other serological polymorphisms, such as RH, GM, and HLA, whose evolutionary mechanisms are also discussed.

Antigens, Differentiation↗

PubMed1992

[Polymorphism of HLA class I loci HLA-A, -B, -C, in the Mandenka population from eastern Senegal].

A sample of 162 Mandenkalu from Eastern Senegal has been typed for three HLA class I loci: HLA-A, -B and -C. The Mandenka population presents a very high genetic variability with 15 alleles for locus A, 24 alleles for locus B, and at least 8 alleles for locus C. The calculated heterozygosities for the three loci A, B, and C are respectively 0.884, 0.944 and 0.829. The Mandenkalu allelic frequencies are close to that found in other sub-Saharan populations. They show, however, some peculiarities like the occurrence of the Bw 56 allele and the high frequencies of both B5 and B35.

Alleles↗

PubMed1992

HLA-DR polymorphism in a Senegalese Mandenka population: DNA oligotyping and population genetics of DRB1 specificities.

HLA class II loci are useful markers in human population genetics, because they are extremely variable and because new molecular techniques allow large-scale analysis of DNA allele frequencies. Direct DNA typing by hybridization with sequence-specific oligonucleotide probes (HLA oligotyping) after enzymatic in vitro PCR amplification detects HLA allelic polymorphisms for all class II loci. A detailed HLA-DR oligotyping analysis of 191 individuals from a geographically, culturally, and genetically well-defined western African population, the Mandenkalu, reveals a high degree of polymorphism, with at least 24 alleles and a heterozygosity level of .884 for the DRB1 locus. The allele DRB1*1304, defined by DNA sequencing of the DRB1 first-domain exon, is the most frequent allele (27.1%). It accounts for an unusually high DR13 frequency, which is nevertheless within the neutral frequency range. The next most frequent specificities are DR11, DR3, and DR8. Among DRB3-encoded alleles, DR52b (DRB3*02) represents as much as 80.7% of all DR52 haplotypes. A survey of HLA-DR specificities in populations from different continents shows a significant positive correlation between genetic and geographic differentiation patterns. A homozygosity test for selective neutrality of DR specificities is not significant for the Mandenka population but is rejected for 20 of 24 populations. Observed high heterozygosity levels in tested populations are compatible with an overdominant model with a small selective advantage for heterozygotes.

Base Sequence↗

PubMed1991

Spatial differentiation of RH and GM haplotype frequencies in Sub-Saharan Africa and its relation to linguistic affinities.

This study analyzes patterns of variation in eight GM and seven Rhesus (RH) haplotypes across sub-Saharan Africa. We examine the concordance with genetic patterns of both geographic and language-family relationships by spatial analysis and ordination techniques. The genetic variation has significant spatial structure, but positive autocorrelation declines neither asymptotically nor proportionally with increasing distance. Evidently, neither isolation by distance with increasing distance. Evidently, neither isolation by distance nor clinical migration-selection models account for the observed genetic structure. Language-family relationship is the best predictor of genetic relationship and may reflect historic migrations and expansions of ethnically different peoples within sub-Saharan Africa. Yet the greatest part of the genetic variance remains unexplained by the models we have tested.

Africa, Central↗

PubMed1990

A worldwide population study of the Ag-system haplotypes, a genetic polymorphism of human low-density lipoprotein.

The aim of this investigation is to examine the distribution of the Ag immunological polymorphism in human populations on a worldwide scale and to look for possible explanations of this distribution in the field of modern human peopling history and Ag-system evolution. Extensive Ag-antigene typings were carried out on 13 human population samples, including sub-Saharan African, European, west and east Asiatic, Melanesian, Australian aborigine, and Amerindian groups. Complete Ag-haplotype frequencies were estimated by maximum-likelihood-score procedures, and the data were analyzed by genetic distance computations and principal coordinate projections. With the exception of the Amerindian sample, the Ag polymorphism is shown to be highly polymorphic in all the populations tested. Their genetic relationships appear to be closely correlated to their geographical distribution. This suggests that the Ag system has evolved as a neutral or nearly neutral polymorphism and that it is highly informative for modern human peopling history studies. From the worldwide Ag haplotypic distributions, a model for the Ag molecular structure is derived. According to this model and to the most recent results obtained from molecular data, the establishment of the Ag polymorphism could be explained by several mutations and recombination events between the haplotypes most frequently found in human populations today. As a conclusion, genetic and paleontological data suggest that the genetic structure of caucasoid populations (located from North Africa to India) may be the least differentiated from an ancestral genetic stock. Worldwide genetic differentiations are properly explained as the results of westward and eastward human migrations from a Near East-centered but undefined geographical area where modern humans may have originated. The importance of Ag polymorphism analyses for the reconstruction of human settlement history and origins is discussed in the light of the main conclusions of the most recent genetic polymorphism studies.

Antigens↗

PubMed1990

Interethnic genetic differentiation: GM polymorphism in eastern Senegal.

Analysis of GM polymorphism has been performed on 1,806 individuals representing three sympatric ethnic groups--Bedik, Fulani, and Mandenkalu--of eastern Senegal. Haplotype frequencies estimated by maximum likelihood have been used to compute common genetic pools between the three samples and a number of other sub-Saharan African populations. Despite extreme linguistic and sociocultural differentiations and very high levels of endogamy, especially in the Bedik and Niokholo Mandenkalu, the three populations share about 90%-95% of their haplotype frequencies in a system which commonly provides strong genetic differentiations. This supports the view that, despite its importance at a large continental scale level, as it is discussed for a set of populations from many regions of sub-Saharan Africa, sociocultural differentiation usually has little effect on local genetic diversity.

Demography↗

PubMed1988

Common genetic pools between human populations.

A further inquiry on modern human origins, based on common genetic pool surveys of rigorously selected population samples and highly informative immunological polymorphisms, provides new evidence of an Occidental-Oriental population split as the origin of human gene pool divergences. The most likely ancestral genetic profile is discussed in the context of the debate raised by preliminary DNA restriction fragment length polymorphism studies, which contradict the conclusions drawn from classical blood group analyses.

Biological Evolution↗

PubMedDate not supplied

Genetic differentiation of Yemeni people according to rhesus and Gm polymorphisms.

For introducing Yemeni population in synthesis of genetic relationships of human populations, analysis of rhesus and Gm polymorphisms have been carried out for a population sample of 210 Yemenites. Rhesus haplotype frequencies were compared to those estimated in an original sample of 171 Tunisians and to available data for other populations. Gm haplotype frequencies were introduced in a wide synthesis of genetic relationships for 67 populations from Africa, Europe, the Near East and India. The genetic profile of Yemeni people would be close to that of a highly diversified ancestral population. The first inhabitants of North Africa, the Berbers and Yemenites have very likely a common origin and were not subject to important genetic drift after their geographic differentiation. While, the divergence between Yemenites and their neighbours of sub-Saharan Africa would have occurred with a founder effect and a long isolation. An important parallelism is observed for the Gm system between genetic and linguistic differentiations.

Black People↗

PubMedDate not supplied

Haemoglobin D-Ouled Rabah among the Mozabites: a relevant variant to trace the origin of Berber-speaking populations.

We have studied haemoglobin (Hb) variants and blood groups (ABO, RH, and Kell) in 598 children from the Berber population of the Mzab. Hb D-Ouled Rabah, considered as a private marker of the Kel Kummer Tuaregs, and Hb C were found at the same gene frequency (0.015). Haplotype analysis suggests a single origin to the Hb D mutation. Genetic distances calculated from the blood group data cluster Mozabites and Tuaregs with the other Berber-speaking groups, Arabic-speaking populations being more distant. But, we found no specific relationship between Mozabites and Kel Kummers. Tuaregs in general exhibit features that tend to differentiate them from other Berber-speaking groups. Hb D-Ouled Rabah may be specific of Berber-speaking populations.

Algeria↗