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La drepanocytose resulte d'une mutation unique et son mecanisme physiopathologique a ete minutieusement explore ; elle constitue donc un modele de choix pour aborder le probleme de la variabilite d'expression clinique des maladies monogeniques. Peuvent etre la cible de phenomenes modificateurs : (1) la polymerisation de l'hemoglobine S (diminuee par l'hemoglobine fœtale) ; (2) la concentration intra-erythrocytaire en hemoglobine S, si existe une α-thalassemie concomitante, ou une modification de l'action de facteurs transregulateurs sur l'expression respective des genes foetaux γ-globine et du gene adulte β S -globine ; (3) le profil particulier d'expression de proteines autres que l'hemoglobine dans les reticulocytes de drepanocytaires, car la drepanocytose est aussi une maladie cellulaire et rheologique: anomalies des constituants de la membrane erythrocytaire et de sa permeabilite, phenomenes d'adherence aux parois vasculaires, activation de la cascade de la coagulation, sont tous des processus faisant intervenir des proteines partenaires qui sont, ou pourraient etre, polymorphes.

Previous work has demonstrated that the HbS gene has appeared and expanded three times in Africa in three separate geographic locations and that these three distinct mutational events can be identified by linked DNA polymorphic sites (haplotypes) surrounding the abnormal gene. We have reported that the Senegalese and Beninian haplotypes differ in G gamma expression, mean percentage of HbF, and percentage of dense cells. We now report on the third haplotype, the Bantu, and find that it has intermediate features, namely, the high mean percentage of HbF and low percentage of dense cells associated with the Senegalese haplotype, but with a low percentage of G gamma expression similar to the Beninian haplotype. The distribution of percent HbF is quite different from Senegal haplotype-bearing sickle cell anemia patients since it covers a much wider range. The low G gamma expression is also different from the Beninians since it contains a significant and unique cluster of individuals with lower than 38% G gamma. Interestingly, among the Bantu there is a strong correlation between HbF levels and G gamma expression, which is not seen with the other haplotypes. These findings open the possibility that among the Bantu haplotype-bearing individuals two chromosomal types exist that define different levels of G gamma and HbF expression. Further structural exploration of these two potential subhaplotypes is needed.

Haemoglobin Belfast was initially observed in an Irish patient. The second case, found in a French patient suffering from a metastatic carcinoma, is here described. Both observations are compared from clinical, haematological and biochemical points of view. Functional and spectrophotometrical studies confirmed the slight abnormalities already described.

Hemoglobin D Los Angeles α 2 β 2 121 Gln was found in three members of a French family. The usual technical procedure was modified to exclude acid pH at all stages. The final Edman degradation demonstrated that the residue in the N-terminal position definitely was glutamine.

Summary The application to «unstable hemoglobins of X-ray studies by Dr. Perutz and his coworkers, together with the large number of mutants, have given a new look on this problem. Some years ago, several mechanisms had been proposed to explain the functional troubles, such as increased release of the heme group, weakening of the contacts between unlike subunits and changes in the conformation of the whole molecule. It has become clear that the term itself of «unstable hemoglobins it now obsolete and that the stereochemical explanation, in correlation with the study of physiological data in each different case, is the only one which comes at the molecular level. We made some observations concerning «heat labile hemoglobins, all mutated in the heme pocket. Hemoglobin Koln has been the first «unstable hemoglobin described in 1966 and the best studied since then. All the observed troubles can be explained by the loss of two hemes normally linked to the β chains. It resembles the artificial semi-hemoglobins carrying only two hemes on the α chains. Hemoglobin Hammersmith is a non-cooperative hemoglobin with low oxygen affinity, whose tertiary structure of the β chain is fixed in the deoxy state. Instability in this case is not due to loss of heme but to the formation of abnormal oxidized hemichromes. Hemoglobin Santa Ana is a partially deheminized hemoglobin. It has a high oxygen affinity and a low interaction coefficient. The disruption of the F helix by a new introduced proline, close to the C terminal end of the chain, must be responsible for this feature. Hemoglobin Genova was not possible to isolate from normal hemoglobin A. It does not lose its heme. We have arguments to think, from intraerythrocytic studies, that it has a high oxygen affinity. Hemoglobin Toulouse has a spontaneous tendency to oxidation into a normal ferrihemoglobin. This is due to acidification of the heme pocket. In the well known hemoglobin M Saskatoon, there is a permanent bond between the new introduced tyrosine and the ferric iron of the heme. Intraerythrocytic oxygen equilibrium studies would be explained by an interaction between the normal and the mutated proteins. Comparing all these results makes obvious that each case has a specific disorder pattern. Since this kind of disease is relatively frequent, such studies provide a quick approach of the problem and perhaps a way of diagnosis.

Analysis of the restriction endonuclease Hpa 1-beta globin gene linkage has been performed in a predominantly Arab population of North Africa possessing the sickle (beta A) gene is found associated with a 7.6 kilobase) or 7.0 kb Hpa 1 fragment (54/54 assignable beta A genes), whereas the beta S gene is found associated with a 13 kb Hpa 1 fragment (42/42 assignable beta S genes). The results demonstrate a very tight linkage of the beta S gene to the 13 kb Hpa 1 fragment as well as a very low probability that a beta A gene will be found on a 13 kb Hpa 1 fragment. Thus, the North African population presents a nearly ideal opportunity for prenatal diagnosis solely by Hpa 1-beta globin gene linkage analysis. Additionally, the evidence supports the hypothesis that the beta S gene flowed from West Africa rather than from Arab populations in the Middle East.

Haemoglobin Belfast was initially observed in an Irish patient. The second case, found in a French patient suffering from a metastatic carcinoma, is here described. Both observations are compared from clinical, haematological and biochemical points of view. Functional and spectrophotometrical studies confirmed the slight abnormalities already described.

A great deal of work has been in the recent years concerning sickle cell anemia, both its theoretical aspects and its medico-social consequences being involved. From the pathophysiological point of view, investigations have resulted in a better knowledge of the mechanism of the hemoglobin S polymerization. Other factors such as the role of the membrane, the ionic environment, the rheologic conditions have also been emphasized. These known disorders may explain the high clinical polymorphism of the disease. They are also the basis of a research for a potential specific treatment. Two factors have been specially investigated as potentially responsible for a benign course of the disease, namely fetal hemoglobin and an associated alpha-thalassemia. As a new field of investigation, a DNA polymorphism close to the beta-gene and linked to the mutation itself has been demonstrated. It proves the pluricentric origin of this mutation. It is also a tool for antenatal diagnosis of the homozygous forms of the disease using amniotic fluid cells. Finally the possible direct culture of P. falciparum as allowed a better understanding of the equilibrium between malaria and sickle cell anemia.

The molecular evolution is considered in several protein families. It can be studied with the data of an entirely known structure, like in hemoglobin or cytochrome, or of only partial structural data, as for proteases or immunoglobulins. In the case of isozymes the study of physico-chemical and kinetic properties is more indirect. Finally, it is shown that the molecular mechanisms are always the same, happening probably at the same frequency, the differences being due to a variable selection by molecular constraints and adaptation to the environment.

A new variant, Hb Barcelona (beta 94 Asp leads to His) found in a Spanish family presenting with a mild polycythemia, is described. Its increase in oxygen affinity is explained by the rupture of the salt-bridge between beta 94 Asp and beta 146 His which normally stabilizes the deoxystructure and accounts for approximately half of the Bohr effect. A comparison between the estimated oxygen transport to the tissues by the blood from a patient with Hb Kempsey and that of the patients with Hb Barcelona showed, in the latter cases, that an almost normal oxygen delivery was obtained by the increase of the hemoglobin level.

Hemoglobin J Mexico has been found in five generations of a large Algerian family. Nine subjects have 55% Hb J although their parents, siblings and offspring may have 31%, the usual quantity found in heterozygotes. Those with 55% Hb J are considered to be homozygous for a chromosome carrying both a normal alpha chain locus and a locus for alphaJ. The proportion of the abnormal hemoglobin in all the subjects is in favor of an unequal expression of both loci, the amount of protein synthesis directed by the alpha J gene being greater than that directed by the alpha A. In two heterozygotes a slightly higher proportion of the Hb J (38%) suggests the presence of a single normal alpha chain locus in trans. An associated alpha-thalassemia was excluded by biosynthetic studies in this family.

We have determined the frequency of deletional alpha-thalassemia in black populations in the USA and Africa that harbor sickle cell anemia. In normals, the frequency of the chromosome bearing a deletion of one of the two normal alpha gene loci, designated (-alpha), ranged from 0.12 to 0.16, and in sickle trait subjects, the frequency ranged from 0.18 to 0.20. By contrast, in sickle cell anemia subjects, the frequency was significantly greater and ranged from 0.22 to 0.33. Analysis demonstrated that the greater frequency in the last group was primarily a result of an increased number of subjects with alpha- thalassemia trait (also called homozygous alpha-thalassemia-2). In addition, the frequency of the (-alpha) chromosome was found to increase progressively with age, supporting the hypothesis that alpha- thalassemia is favorable to the survival of subjects with sickle cell anemia. Thus, individuals who inherit alpha-thalassemia and sickle cell anemia may represent a subgroup of patients with a longer life expectancy.