Dominique Labie

Hematologically and genetically distinct forms of sickle cell anemia in Africa. The Senegal type and the Benin type.

Patients with sickle cell anemia vary in the hematologic and clinical features of their disease, in part because of variability in the presence of linked and unlinked genes that modify the expression of the disease. The hemoglobin S gene is strongly linked to three different haplotypes of polymorphic endonuclease-restriction sites of the beta-like gene cluster (genes in the vicinity of the beta-globin gene)--one prevalent in Atlantic West Africa, another in central West Africa, and yet another in Bantu-speaking Africa (equatorial, East, and southern Africa). We have studied the differences in the hematologic characteristics of patients with sickle cell anemia from the first two geographical areas. We find that the Senegalese (Atlantic West Africa) patients have higher levels of hemoglobin F, a preponderance of G gamma chains in hemoglobin F, a lower proportion of very dense red cells, and a lower percentage of irreversibly sickled cells than those from Benin (central West Africa). We interpret these data to mean that the gamma-chain composition and the hemoglobin F level are haplotype linked and that the decrease in the percentage of dense cells and irreversibly sickled cells is secondary to the elevation in the hemoglobin F level. Patients with sickle cell anemia in the New World probably correspond to various combinations of these types, in addition to the still hematologically undefined haplotype associated with sickle cell anemia in the Bantu-speaking areas of Africa.

The amino acid sequence of the δ-β chains of hemoglobin LeporeAugusta = LeporeWashington

A hemoglobin Lepore (LeporeAugusta) from a subject of Italian origin has been studied by isolating the polypeptide chains, by determining their amino acid composition and that of tryptic peptides from the δ-β chains, and by examining the sequence of certain critical tryptic peptides. The results confirm the ideas of Baglioni that in this particular type of hemoglobin Lepore a non-homologous crossing over of the β and δ genes has occurred in such a way that the δ-β chain of Lepore hemoglobin has the sequence of the δ chain from residues I to 87 and of the δ chain from residues 116 to 146. Inasmuch as the β and δ chains have identical sequence between residues 88 and 115, the determination of sequence does not establish at what point between residues 87 and 116 the crossing-over occurred.

Long-term hydroxyurea treatment in young sickle cell patients.

Hydroxyurea is the first drug that, under well-organized, large-scale trials in adults, has shown a beneficial effect on the clinical course of sickle cell disease. Several small-scale trials have been conducted in children, but they used different therapeutic schedules, and only one was a single-blind crossover trial. Still, children are clearly good responders to the treatment because a rapid clinical improvement was observed, with decreased frequencies of vaso-occlusive crises, acute chest syndromes, and transfusion requirements. Despite large interindividual variations, virtually all the children studied increased their fetal hemoglobin, mean corpuscular volume, and total hemoglobin. Follow-up varied from 6 months to 59 months. More than in adults, the fetal hemoglobin increase was sustained, and few side effects were observed. Large-scale, placebo-controlled studies seem no longer needed. Guidelines concerning patient selection, dosing schedules, and monitoring protocols as well as exhaustive registries for the detection of long-term side effects are necessary.

Molecular basis of α-thalassemia in Sicily

Abstract To evaluate the allelic frequency and genetic diversity of α-thalassemia defects in Sicily, both epidemiological and patient-oriented studies were carried out. For the epidemiological study, phenotypic data were collected on more than 1000 Sicilian individuals. Among them, 427 were explored at the molecular level for nine α-thalassemic variants known to be common in the Mediterranean region. Our data reveal an allele frequency of 4.1% for α+-thalassemia matching that of β-thalassemia in this region. The presence of α°-thalassemia (––MEDI and ––CAL) was observed only in the group of referred patients. Newly acquired nucleotide sequence data on the deletional breakpoint of ––CAL allowed us to design a simple PCR-based procedure for exploring this allele. The data also provide additional information concerning the genetic mechanisms involved in such large deletions.

Two new hemoglobin variants with deletion: Hemoglobin tours: Thr β 87 (F3) deleted and hemoglobin St Antoine: Gly-Leu β 74–75 (E 18–19) deleted. Consequences for oxygen affinity and protein stability

Abstract Two new variants of abnormal hemoglobins with deletions have been identified. In Hemoglobin Tours, the deletion of residue Thr β 87 (F3) displaces Leu β 88 (F4) which appears to be very important in the heme-globin binding, and the consequence is a spontaneous loss of heme. In Hemoglobin St Antoine, the deleted segment Gly-Leu β 74–75 (E 18–19) is the end of helix E and close to a loose zone. Although it is in the vicinity of one of the 2,3-diphosphoglycerate binding sites, it has apparently only minor consequences for the functional properties of the molecule.

Functional properties of hemoglobin Hammersmith

Summary Hemoglobin Hammersmith β 42 (CD 1) Phe → Ser is an unstable hemoglobin with low oxygen affinity. From studies made in the intact cells, the main compensatory mechanism for the decreased oxygen affinity was found to be a Bohr effect, the 2.3 DPG being only moderately high. Moreover the molecular mechanisms of the instability seem to be due mostly to the formation of hemichromes. They appeared exceptionnally fast in vitro, and attained completion within one hour. Even though they were still chemically reducible, they were no longer reducible by a highly purified NADH-methemoglobin reductase preparation.

Dissection of the association status of two polymorphisms in the β-globin gene cluster with variations in F-cell number in non-anemic individuals

Expression of fetal hemoglobin (Hb F) is under polygenic control involving determinants both linked and unlinked to the β‐globin gene cluster on chromosome 11. Variations in the DNase I‐hypersensitive site 2 of the locus control region (LCR‐HS2) and a C → T change at position −158 from the Gγ‐gene (detected as an XmnI polymorphism) correlate with the high level of Hb F expression in patients with sickle‐cell anemia and β‐thalassemia. Interpretation of data under these conditions of anemic stress is difficult because the preferential survival of Hb F‐containing erythrocytes (F‐cells) may not reflect the true status of Hb F expression. We investigated the relationship between these markers and Hb F expression in terms of F‐cell levels in 48 unrelated non‐anemic AS heterozygotes from Sicily. The βS‐chromosome of all these individuals was of the Benin haplotype and they differed only by their βA chromosomes. We demonstrate that F‐cell expression is more strongly associated with LCR‐HS2 polymorphism than with XmnI polymorphism. The observed association between XmnI polymorphism and Hb F expression is very likely to be due to linkage disequilibrium with LCR‐HS2 sequences. Am. J. Hematol. 56:239–243, 1997.

Disturbed hemoglobin synthesis during erythroleukemia.

Summary Biosynthetic disturbance in human erythroleukaemia has been investigated for several years. A first noticeable feature was the permanent existence of two red cell populations easily separated according to their specific gravity; only the lighter fraction showed abnormalities, among them an exceptionnaly high proportion of hemoglobin H. A clonal origine of the abnormal cells is suggested. A large and very unusual pool of β 2 dimer could be demonstrated: they were no precursors of normal haemoglobin α 2 β 2 and did not seem to be in equilibrum with the tetramer β 4 but to be only its precursor. Some important differences with genetically determined α thalassemia were demonstrated. The abnormal cells seem to have a faster maturation than the normal ones; it is also likely that the trouble is essentially an increased β chain synthesis, rather than a diminished α chain synthesis. It has been ruled out that the trouble is at the rate assembly level. Moreover, as opposed to thalassemia, the unbalance decreases during erythrocytic maturation.

BCL11A represses HbF expression and varies during ontogeny

Signification du taux d’hemoglobine fœtale L’expression de differentes hemoglobines (Hb) au cours du developpement ontogenique correspond a l’activation successive des genes codant pour les chaines de globine, situes sur le chromosome 11p15 dans l’ordre de leur expression1. Au niveau du locus β-globine, deux commutations (switch) sont observees : la premiere, precoce au cours de la vie embryonnaire, correspond a l’activation des genes γ-globine ; la seconde, perinatale, correspond a l’extinction incomplete de ces derniers et a l’activation des genes adultes δet β-globine. Ce switch a fait l’objet de multiples travaux ; c’est, en effet, un modele d’etude, mais son importance physiopathologique est majeure, car le taux d’Hb fœtale (HbF) est un element essentiel modulant la gravite des hemoglobinopathies, drepanocytose et β-thalassemies. Ce taux d’HbF se presente en clinique comme un trait quantitatif dont on a cherche les facteurs de regulation. Dans un nombre limite de cas, on a observe l’existence concomitante d’une PHHF (hereditary persistance of fetal hemoglobin) de transmission mendelienne. Deux types de PHHF ont ete caracterises, soit des deletions impliquant tout ou partie du gene b-globine, soit des mutations (le plus souvent ponctuelles) dans la region promotrice de l’un des genes g-globine. L’existence d’une distribution inegale de l’HbF residuelle