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Biomedical subjects

D Labie

Publications and source records attributed to D Labie.

At least 19 recordsLinked to original sources
PubMed1992

[Genetic aspects of sickle cell anemia].

The genetics of sickle cell anemia may be considered as a model. Its mendelian transmission was hypothesized even before the molecular era. Once the mutation identified, it could be studied at the protein and DNA level; a consistent pathophysiological mechanism was proposed; the various genetic forms of the disease could be identified; the way by which a balanced polymorphism with Plasmodium falciparum malaria is obtained was analyzed. More recently, investigations were run in order to understand how modulating, or epistatic factors could modify the pathophysiological mechanism and contribute to the high clinical diversity of the disease. Several factors have been identified, among which a concomitant alpha-thalassemia, an overproduction of fetal hemoglobin, due either to an activation of the gamma genes or to an increase of the F-cell number, and finally a quantitative control of the beta s chains themselves. Such a high number of genetic active factors questions the concept itself of a monogenic disease.

Anemia, Sickle Cell↗
PubMed1992

DNA sequence variation in a negative control region 5' to the beta-globin gene correlates with the phenotypic expression of the beta s mutation.

The clinical diversity of sickle cell anemia is strongly related to the degree of intracellular hemoglobin S (Hb S) polymerization, which in turn is dependent on the intracellular concentration of Hb S. We have recently defined a region of DNA approximately 500 bp 5' to the human beta-globin gene that acts as a silencer for the transcription of this gene and have shown that a polymorphism in this sequence is associated with a thalassemic phenotype of the beta-globin gene. In this work we have examined the correlation of DNA sequence polymorphisms in this silencer with binding of a previously identified putative repressor protein, BP1, and with the expression of Hb S in individuals heterozygous for the beta s allele. It was found that specific configurations of the motif, (AT)x(T)y, are homogeneous for the major haplotypes of the beta-globin gene cluster described on beta s chromosomes. Binding of BP1 was measured to DNA of three haplotypes: Indian, Benin, and Bantu. BP1 binds most tightly to DNA of the Indian haplotype, and these patients produce less beta s protein than Benin patients, whose DNA exhibits weaker affinity for BP1. Binding of BP1 is the weakest to DNA of the Bantu haplotype, which is associated with clinically more severe sickle cell symptoms. These data are consistent with the hypothesis that these polymorphisms may not be neutral and that the DNA sequence at this site may affect the expression of the beta s gene. Such an effect may be synergistic with other genetic variables, such as fetal hemoglobin levels, F-cell numbers, and the number of alpha-globin genes, in determining intracellular polymerization and, thus, the severity of the sickle cell syndromes.

Africa↗
PubMed1992

Presence of an African beta-globin gene cluster haplotype in normal chromosomes in Sicily.

African admixture in Sicily has been long suspected because of the presence of the sickle gene. Nevertheless, the degree of African admixture cannot be derived from the study of HbS frequency, since this gene was most likely expanded by the selective pressure of malaria, for a long time endemic to the region. We have examined 142 individuals from the Sicilian town of Butera (12% sickle trait) to search for other markers of the globin gene cluster less likely to be selected for by malaria. The TaqI polymorphism in the intervening sequences between the two gamma genes is informative. We have found only two instances of this African marker (TaqI(-)) among 267 normal chromosomes, demonstrating that the admixture occurred at a much lower level than previously thought.

Adolescent↗
PubMed1992

A novel sickle cell mutation of yet another origin in Africa: the Cameroon type.

The sickle cell mutation (beta s) arose as at least three independent events in Africa and once in Asia, being termed the Senegal, Benin, Bantu and Indian types respectively. An investigation in Cameroon was carried out to determine whether the atypical sickle genes observed in the neighboring countries are the result of recombination or the presence of a sickle cell mutation of a different genetic origin. It was conducted on 40 homozygous SS patients followed at the Blood Transfusion Center in the capital city of Yaoundé. On 80 beta s chromosomes, 13 exhibited a novel polymorphic pattern that was observed three times in the homozygous state. This chromosome contains an A gamma T gene. The restriction fragment length polymorphism haplotype is different from all the other beta s chromosomes in both the 5' and 3' regions, but has previously been reported in sporadic cases. The (AT)8(T)5 sequence in the -500 region of the beta gene is specific and different from that of the Senegal, Benin, Bantu or Indian beta s genes. All the carriers of this specific chromosome belong to the Eton ethnic group and originate from the Sanaga river valley. This observation strongly argues for yet another independent origin of the sickle cell mutation in Africa, here referred to as the "Cameroon type". The Benin haplotype and a Benin/Bantu recombinant haplotype have been observed in the other studied populations: Ewondo, Bamiléké, Bassa, Yambassa and Boulou.

Anemia, Sickle Cell↗
PubMed1992

A haplotype-linked four base pair deletion upstream of the A gamma globin gene coincides with decreased gene expression.

During normal human development, a switch is classically observed in the relative expression of the two gamma globin genes, the G gamma/A gamma ratio varying from 70/30 at birth to 40/60 by the end of the first year. An exception to this developmental pattern is linked to the presence of an XmnI restriction site at a position -158 to the Cap site of the G gamma gene. Another exception is observed in individuals homozygous for two easily detectable variations of the A gamma gene: the presence of a threonine residue at codon 75 and a HindIII site within the second intron. A 4-bp deletion has been described around position -225 in some thalassemic patients presenting with these variations. In this study, we find this deletion to be haplotype-linked in a series of 156 individuals of various ethnic origins and presenting with various normal and pathological phenotypes. In sickle cell patients heterozygous for this 4-bp deletion, the relative expression of the A gamma genes on the two chromosomes can be measured by estimating the A gamma T and A gamma I chains, the former always being synthesized at a lower rate. These results suggest a functional role for the deleted sequence.

Base Sequence↗
PubMed1992

Importation route of the sickle cell trait into Portugal: contribution of molecular epidemiology.

To elucidate the origin and spread of the sickle cell trait into the Portuguese population, we examined nine polymorphic DNA markers within the beta globin gene cluster defining the haplotype. The population sample included 64 sickle-cell-gene-bearing individuals from defined Portuguese-speaking white, black, and Asian Indian populations. The nature and geographic distribution of the different beta S haplotypes in Portugal suggest that the sickle cell trait has been imported twice: between the eighth and the thirteenth centuries from the Mediterranean basin (in association with the Benin haplotype) and after the fifteenth century from black Africa over an Atlantic route (Senegal and Bantu haplotypes).

Genetics, Population↗
PubMed1992

Rapid and direct detection of the most frequent Mediterranean beta-thalassemic mutations by multiplex allele-specific enzymatic amplification.

A rapid nonradioactive method for the diagnosis of the most frequent Mediterranean beta-thalassemic mutations is described based on a multiplex allele-specific polymerase chain reaction (PCR). This method allows direct detection of normal or mutated alleles on genomic DNA. We have used this approach to detect the most frequent Mediterranean mutations: IVS-1 nt 110 (G----A) and 39 nonsense (C----T). For each mutation three allele-specific oligonucleotides were used: one common upstream primer and two downstream primers differing in their terminal 3' nucleotide (one specific for the normal allele and one for the mutant allele). For each sample two PCR reactions were performed in parallel using in one case IVS-1 nt 110 and codon 39 normal primers and in the second case using the corresponding mutated primers. In both cases the different PCR fragments were visualized. After optimization these primers directed only amplification of their complementary allele. A single blind study was performed on the DNA of 18 individuals who were homozygous or heterozygous for these mutations. In comparison with a parallel investigation, using oligonucleotide probes, all the results were unambiguous. This diagnosis method, which is rapid, easy, direct, and inexpensive, allows the screening of a population group, including heterozygotes, which is required from an epidemiological and anthropological point of view. It could be extended to the large series screening of haplotypes before targeted diagnosis of various genetic diseases.

Algeria↗
PubMed1991

Increased protein binding to a -530 mutation of the human beta-globin gene associated with decreased beta-globin synthesis.

Although some cases of the syndrome of hereditary persistence of fetal hemoglobin (HPFH) have been correlated with mutations causing a change in the binding of trans-acting factors to DNA sequences flanking the gamma-globin gene, this mechanism has not been described in beta-thalassemias upstream of the canonical promoter of the beta-globin gene. In this report we describe such a change in binding of a protein that may explain a silent carrier phenotype of beta-thalassemia. We have previously demonstrated the binding of a protein (BP1) derived from a nuclear extract of human K562 cells to DNA 5' to the human beta-globin gene in a region having a negative regulatory function. The binding of BP1 in this region can be detected by DNAse I footprinting and by gel mobility shift analysis. We have now compared binding of BP1 to the normal sequence and a mutated sequence (+ATA/-T at -530 bp from the cap site) from the silent carrier of beta-thalassemia. Using mobility shift assays we show that BP1 binds about nine times more strongly to the mutated sequence than the normal sequence. These results suggest the possibility that the decreased expression of the beta-globin gene exhibited by the carrier may be due, at least in part, to tighter binding of a protein which functions as a negative control element or repressor.

Base Sequence↗
PubMed1991

Preliminary report on the use of desferrioxamine in the treatment of Plasmodium falciparum malaria.

The administration of 0.5 g (IM) of desferrioxamine every 12 hr for 3 days with 25 mg/kg (total dose for three days) of chloroquine abated the parasitemia of Plasmodium falciparum infected individuals more rapidly than chloroquine alone. Two patients with in vitro evidence of total or partial resistance to chloroquine also were successfully treated with the combination of drugs, and were free of parasitized red cells by day 7. Further clinical trials and development of desferrioxamine in the treatment of P. falciparum are warranted.

Animals↗
PubMed1991

Origin and spread of beta-globin gene mutations in India, Africa, and Mediterranea: analysis of the 5' flanking and intragenic sequences of beta S and beta C genes.

Nucleotide polymorphisms of both the 5' flanking and intragenic regions of the human beta-globin gene were investigated by directly sequencing genomic DNA after amplification by the polymerase chain reaction in 47 subjects homozygous for the beta S or the beta C mutation. The sickle-cell mutation was found in the context of five different haplotypes defined by eight nucleotide substitutions and various structures of a region of the simple repeated sequence (AT) chi Ty. All subjects from the same geographic origin bear an identical chromosomal structure, defining the Senegal-, Bantu-, Benin-, Cameroon-, and Indian-type chromosomes. These results strengthen our previous conclusions about the multiple occurrence of the sickle-cell mutation. The Benin-type chromosome was also found among Algerian and Sicilian sickle-cell patients, whereas the Indian-type chromosome was observed in two geographically distant tribes, illustrating the spread of these sickle-cell genes. We also found that the intragenic sequence polymorphisms (frameworks) are not always in linkage disequilibrium with the BamH I polymorphism downstream from the beta-globin gene, as had been previously observed. Finally, we present a tentative phylogenetic tree of the different alleles at this locus. Some polymorphisms of this sequence might be contemporary with our last common ancestor, the great apes, that is, about 4-6 millions years old.

Africa↗
PubMed1989

[Treatment of homozygote beta thalassemia in Algiers. A 5-year follow-up of 66 patients].

During the years 1982-1987, 66 patients with homozygous beta-thalassaemia were treated at the blood transfusion centre of Algiers. The patients, aged from 1 to 23 years in 1982, came from 48 families, 30 of which were issued from consanguinous unions. The patients fell into three groups according to the early institution and quality of treatment (blood transfusions, antibiotic therapy, desferrioxamine given when available). The beneficial clinical effects observed (satisfactory growth and development, reduction of splenomegaly and hypersplenism, attenuation of craniofacial malformations, performance at school) seemed to be directly related to the mean haemoglobin level prior to transfusion and to the early institution of treatment. Four patients died of anaemia and haemochromatosis. The incidence of viral contamination was 27.5 per cent for the hepatitis B virus and nil for the human immunodeficiency virus.

Adolescent↗
PubMed1989

[Intermediate homozygous beta-thalassemia with high fetal hemoglobin synthesis. Molecular analysis].

The intermediate character of beta-thalassaemia may be due to a molecular cause capable of reducing the unbalance between alpha and non-alpha chains. We report the case of a child born of consanguineous parents and homozygous for beta-thalassaemia. The patient was irregularly transfused until puberty. His haemoglobin level was around 10 g/dl, and in his erythroid line only foetal haemoglobin was synthesized, except for small amounts of haemoglobin A2. An in vitro study of globin chains biosynthesis confirmed the total absence of beta chains synthesis, and the molecular defect was characterized. This was deletion of a colon 6 nucleotide on both chromosomes, making the messenger RNA unstable and non-traducible. The initial diagnostic approach in this patient included the indirect determination of restriction polymorphism (Orkin's halotype IX), a search for the presence or absence of a nonsense codon 39 often associated with haplotype IX, and the demonstration of a frameshift in the reading phase of codon 6. The very high synthesis of foetal haemoglobin in this patient seems to be linked with a C----T substitution in -158 of the G gamma gene creating an Xmnl site and a gamma phi beta (+-++) subhaplotype which appears to be related in all haemoglobinopathies to an increased synthesis of foetal haemoglobin with predominant G gamma chain.

Adult↗