We have studied 42 homozygous 3-thalassemia patients from Algeria and 34 sickle cell anemia patients from Senegal and Benin, determinin* the relationship between haplotypes, Hb F, and G7yglobin/ -globin ratios. Populations selected have a high frequency of haplotype homozygotes because of consanguinity (Algeria) and geographic homogeneity (West Africa). We find in (-thalassemia In addition, haplotypes IX, m, and Senegalese sickle cell anemia patients exhibit hematological amelioration of their disease. Conversely, haplotypes I, V, and A in thalassemia pa-
To test the hypothesis advanced by Gilman and Huisman that the -158 site 5′ to the G gamma gene determines the G gamma expression after the first 4 months of life, we have examined DNA from sickle cell anemia (SS) patients from Africa and beta-thalassemic homozygotes from Algeria. We find that the Xmnl site is strongly linked to the Senegal haplotype among SS patients, to haplotype IX (most probably identical to the Senegal haplotype), and to haplotype III among the Algerian thalassemics. Thalassemics with haplotypes I/I and V/V have no Xmnl site and low G gamma expression. In contrast, beta-thalassemia- associated haplotype II (also characterized by high G gamma expression) fails to exhibit the Xmnl site. We conclude that, although highly correlated, the -158 C----T substitution does not perfectly predict the presence of high G gamma expression. These findings also exclude the possibility that the Xmnl site is solely involved in the determination of high G gamma expression and suggest that either several different site substitutions in the area 5′ to the gamma gene might have the same effect or that, alternatively, the Xmnl site and its surrounding area is not involved in G gamma expression and may be only in linkage disequilibrium with a controlling sequence elsewhere.
An epidemiological molecular study was carried out to evaluate the spectrum and allelic frequency of alpha-thalassemia (alpha-thal) defects in Algeria. A series of 153 randomly selected blood donors was screened for 10 alpha-thal alleles described in the Mediterranean area. In addition, six unrelated cases with hematological and biochemical data suggestive of Hb H disease were investigated. Our data revealed an allele frequency of 4.6%. The presence of alpha(0)-thal determinants (-alpha(20.5) and --MED I) was observed both in Hb H patients and in the randomly collected samples. Overall, the -alpha(3.7) deletion was the most prevalent allele (2.9%), followed by the alpha(Nco I)alpha (HBA2:c.1A>G) allele (0.6%) and by the alpha(Hph I)alpha (HBA2:c.95 + 2_95 + 6delTGAGG), -alpha(20.5), --(MED I) alleles (0.3% each). The -alpha(4.2) deletion was observed in only one Hb H patient. These results outline the heterogeneity of the alpha-thal alleles in Algeria which reflects the anthropological history of the country. Because of their frequency, alpha-thal alleles are probably frequent modulators of prevalent beta-globin gene-related hemoglobinopathies in Algeria.
We report here on the final results of an epidemiological survey involving 177 beta-thalassaemic chromosomes in Algeria. Four common mutations account for 86% of the chromosomes, the other ones carrying nine other rare mutations. Combination of these results with those of other smaller regional epidemiological studies indicates the existence of still a wider range of mutations. The nature and frequencies of these mutations, their linkage with RFLP-haplotypes, agree well with the history of the region. Knowledge of this spectrum of mutations enables the design of a diagnosis strategy that takes into account the local economical constraints.
An evaluation of beta thalassaemia mutations and the associated chromosomal haplotypes has been made among Algerian thalassaemic patients in this extended series. The major features of our findings are: (i) due to elevated proportion of consanguinity, the frequency of true homozygotes for a defect is high; (ii) Despite this high homozygosity within families, the number of molecular defects resulting in beta thalassaemia are very heterogeneous within this population. This is exemplified not only by the high heterogeneity of haplotypes and associated mutations, but also by the definition of several new haplotypes, among which two of them were found to be associated with novel mutations. Family studies have been performed in parallel to evaluate the degree of feasibility of antenatal diagnosis in this population.
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