[The problem of sickle cell disease in Africa]. / La drépanocytose: problème de l'Afrique.

Sickle cell disease is a genetic blood disorder caused by a glutamic to valine acid substitution in the beta chain of the hemoglobin protein. It was first reported in the United States where most research has been carried out on subjects of African descent. It is diffused throughout the world. Epidemiological data show that the highest incidence of sickle cell anemia is in sub-Saharan Africa where the severest forms are often fatal in children under the age of 5 years. The clinical course of the disease in Africa is comparable to that described in industrialized countries. The three cardinal symptoms are hemolytic anemia, painful episodes, and susceptibility to infection. Genotype and phenotype variations have been observed from one zone to another in Africa. Greater severity is due to a combination of various factors including constant coexistence with Plasmodium falciparum malaria and omnipresence of pyogenic factors as well as to the unfavorable demographic setting involving endogamy, poor healthcare facilities, and poor socio-economic conditions. A hundred years of research has provided a good understanding of the pathophysiological mechanisms that can sometimes be improved by to primary hydroxyurea therapy. Sickle cell disease remains a major health problem in Africa where patients do not currently benefit from the same treatment as in industrial countries.

[Pathophysiology of sickle cell disease]. / Physiopathologie de la drépanocytose.

It has been 100 years since Herrick published the first medical case report of sickle cell disease. In 1949, Pauling discovered hemoglobin S (HbS). As early as the 1960-70s, emerged a coherent detailed molecular-level description of pathophysiology of sickle disease. It involved polymerization of deoxyhemoglobin S with formation of long fibers inside red blood cells (RBC) causing a distorted sickle shape and shortened lifespan. These changes constitute the basic disease process and account for hemolytic anemia and for obstructive events underlying vasoocclusive crises (VOC). However, they do not explain the mechanisms that trigger VOC. The purpose of this review is to present recent data on dehydration of sickle cell RBC, abnormalities in RBC adhesion to the vascular endothelium, the role of inflammatory events and of activation of all cells in the vessel, and abnormalities of vascular tone and carbon monoxide metabolism. These data provide new insight into the pathophysiology of the first molecular disease.

Erythroid adhesion molecules in sickle cell disease: effect of hydroxyurea.

In sickle cell disease, the complex scenario of vaso-occlusive crisis (VOC) typical of this disease is clearly multifactorial and not fully understood. Cell-cell and cell-cell matrix interactions mediated by adhesive molecules present on blood cells and endothelial cells (ECs) are thought to play an important role. Early studies have shown that sickle red blood cells (RBCs) are abnormally adherent to ECs and some of the molecules involved in these interactions have been identified, such as the alpha4beta1 integrin and CD36, exclusively present on stress reticulocytes, and CD47 on mature RBCs. More recently, attention focused on Lu/BCAM, the unique RBC receptor for laminin, and on ICAM-4, a red cell-specific adhesion receptor, which is a ligand for a large repertoire of integrins (alphaLbeta2, alphaMbeta2, alphaxbeta2, alphaVbeta3). The counter-receptors on ECs and the role of plasma proteins forming bridges between blood cells and ECs have been clarified in part. It has also been shown that reticulocytes from SCD patients express higher levels of alpha4beta1 integrin and CD36, and that under hydroxyurea (HU) therapy, both cell adhesion to ECs or extracellular matrix proteins and the levels of these adhesion molecules are reduced. These findings are consistent with the view that enhanced adhesion of blood cells to ECs is largely determined by the membrane expression level of adhesion molecules and could be a crucial factor for triggering or aggravating vaso-occlusion. In SCD patients, membrane expression of Lu/BCAM (and perhaps ICAM-4) is enhanced on RBCs whose adherence to laminin or ECs is also increased. Interestingly, Lu/BCAM- and ICAM-4-mediated adhesion are enhanced by the stress mediator epinephrine through a PKA-dependent pathway initiated by a rise in intracellular cAMP and leading to receptor activation by phosphorylation according to the same signaling pathway. More recently, studies based on quantitative expression analysis of adhesion molecules on RBCs and during erythroid differentiation in patients undergoing HU therapy, surprisingly revealed that Lu/BCAM level was enhanced, although alpha4beta1, CD36 and ICAM-4 (to a lower extent) levels were indeed reduced. CD47 and CD147 expression were also enhanced in HU-treated patients. Based on these findings we suggest that the signalization cascade leading to receptor activation rather than the expression level only of adhesion molecules may be the critical factor regulating cell adhesion, although both mechanisms are not mutually exclusive.

Determination of coronary flow reserve by digital angiography: validation of a practical method not requiring power injection or electrocardiographic gating.

Although coronary flow reserve is a well established measure of the physiologic significance of atherosclerotic stenosis, cumbersome methodology has prevented its widespread clinical application. This study evaluated a new simplified method of measuring coronary flow reserve based on indicator-dilution analysis of hand-injected digital coronary arteriograms. In five dogs, the circumflex artery was instrumented with an angiographic catheter, an electromagnetic flow probe and a pneumatic occluder. For each of 18 stenoses of varying severity, arteriograms were obtained under basal conditions and during papaverine-induced hyperemia. A pair of background-corrected arterial time-density curves was generated for each stenosis by off-line computer analysis of the circumflex artery arteriograms. Coronary flow reserve was calculated from the measured areas of the time-density curves and the known volume of contrast medium used to produce each curve. Angiographic flow reserve ranged from 0.9 to 6.1 (mean 2.99), whereas electromagnetic flow reserve ranged from 0.7 to 6.9 (mean 3.02). Angiographic and electromagnetic measurements of coronary flow reserve correlated well (r = 0.86). This study establishes that indicator-dilution analysis of 30 frames/s digital coronary arteriography permits the accurate determination of coronary flow reserve. The technique described employs hand injection of small doses of radiographic contrast medium using conventional catheters, and should be readily applicable to the study of human coronary artery disease.

Left heart opacification with peripheral venous injection of a new saccharide echo contrast agent in dogs.

Opacification of the left heart chambers after venous injection of echo contrast agents with transpulmonary capabilities has been difficult to achieve because of a lack of availability of a biodegradable nontoxic agent that produces uniformly small microbubbles. SHU-508 is a new saccharide echo contrast agent that produces bubble sizes from 2 to 8 microns in diameter, capable of traversing the pulmonary capillary bed and resulting in left heart contrast. The echo intensity produced by this agent was compared with that of agitated saline solution, indocyanine green and SHU-454 (another experimental saccharide agent for right-sided contrast) during 136 injections in eight dogs. Videotaped two-dimensional echographic images were digitized and analyzed with the use of videodensitometry for peak right and left ventricular intensity, pulmonary transit times and time of persistence of contrast. The highest right ventricular intensity value (3,594 +/- 1,393) was achieved with SHU-508 (p less than 0.05 compared with the other agents). The right ventricular contrast seen with SHU-508 also persisted for a longer period (22.8 +/- 12 s) than with the standard agents (p less than 0.001). Left ventricular contrast with SHU-508 was visually evident in all 42 injections, whereas the peak left ventricular intensity was 35% as bright as that produced in the right ventricle by the same agent. Peak left ventricular intensity values from SHU-508 were compared with those from agitated saline solution injected from the pulmonary capillary wedge position in four dogs. SHU-508 produced brighter left ventricular intensity (1,281 +/- 607) compared with that obtained with the saline-wedge technique (p les than 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitation of aortic regurgitation by computer analysis of digital subtraction angiography.

Digital subtraction angiography provides the potential to determine aortic regurgitant fraction by computer analysis of time-intensity curves generated from regions of interest positioned over the aorta and left ventricle after aortography. To validate this ability, we studied six dogs instrumented with an electromagnetic flow probe on the ascending aorta. Aortic regurgitation of varying severity was produced by a basket catheter introduced through the right carotid artery. Aortograms were performed using continuous fluoroscopy at 30 frames/s and stored in digital format in a 256 x 256 pixel matrix. An image-processing computer was utilized to plot summated pixel intensity versus time for both the aortic and the left ventricular regions of interest. Regurgitant fraction was calculated from the time-intensity curves using an algorithm analogous to that employed by dye-dilution methods. Regurgitant fraction determined from digital angiography was compared with that obtained by electromagnetic flow and was found to correlate well (r = 0.94, SEE = 7.4%) over a wide range of values. Thus, these data indicate that aortic regurgitant fraction can be accurately determined from computer analysis of digitally acquired aortograms in an animal model of acute aortic regurgitation.

Correlation of continuous wave Doppler velocities with cardiac catheterization gradients: an experimental model of aortic stenosis.

The purpose of this study was to use a canine preparation of experimental aortic stenosis to compare estimates of pressure gradient derived from continuous wave Doppler ultrasound with gradients measured directly by catheterization. Aortic stenosis was created in six mongrel dogs by placing an elastic band around the aorta. Eighty-eight different pressure gradients, ranging from 5 to 160 mm Hg, were produced by variable tightening of the aortic band. Pressure gradients were measured by micromanometer-tipped catheters placed in the left ventricle and aorta. Doppler spectral signals were simultaneously obtained using a 2.0 MHz nonimaging transducer placed directly on the surface of the ascending aorta. Doppler and pressure recordings were analyzed using a custom-designed software program to measure maximal instantaneous, mean and peak to peak gradients, as well as ejection and acceleration times. Maximal instantaneous Doppler gradient showed an excellent linear correlation with maximal instantaneous catheterization gradient (r = 0.98, SEE = 5.3 mm Hg). The correlation of Doppler-estimated maximal gradient to peak to peak catheterization gradient was also linear (r = 0.97, SEE = 6.2 mm Hg) but resulted in a systematic overestimation of pressure drop (mean overestimation = 9.0 mm Hg). Measurement of the Doppler gradient at mid-systole resulted in a more accurate correlation with the peak to peak catheterization gradient (r = 0.98, SEE = 6.1 mm Hg) and eliminated the problem of overestimation.(ABSTRACT TRUNCATED AT 250 WORDS)

Contrast echo washout curves from the left ventricle: application of basic principles of indicator-dilution theory and calculation of ejection fraction.

Time-intensity curves can be obtained from contrast echocardiography of the left ventricle. The purposes of this study were: 1) to verify whether these curves conform to the basic principles of indicator-dilution theory; and 2) to derive indexes of left ventricular ejection fraction from curve analysis. In seven closed chest dogs, 31 doses of the polysaccharide agent SHU-454 were injected into the left ventricular cavity during apical four chamber two-dimensional echocardiography. Data were obtained at different levels of ejection fraction, which were induced by changes in preload, afterload and contractility, and measured by single plane Simpson's rule analysis of digital subtraction left ventriculograms. In a subset of two dogs, eight incremental doses (from 1 to 8 ml) of SHU were injected in the basal state. Contrast echocardiograms were digitized off-line, the mean gray level/pixel of a region of interest inside the left ventricular cavity was measured, and the average value for three systolic frames of each beat was used to obtain time-intensity curves. A good correlation was observed between the peak of the time-intensity curve and the quantity of contrast injected (correlation coefficient r = 0.91 by a logarithmic fit). The echo intensities observed in each animal were subsequently transformed in quantity of contrast according to these functions and their natural logarithm was calculated both with and without background subtraction. All curves relating time and the natural logarithm of the corrected intensity exhibited a descending rectilinear portion (washout) in which the correlation was very good (r = 0.97 +/- 0.02 = mean +/- SD) and which was not significantly affected by background subtraction. The validity of this fit was also unaffected by heart rate (55 to 158 beats/min) and angiographic ejection fraction (22 to 74%), and only minimally influenced by duration of contrast washout (3.3 to 14.6 seconds). Ejection fraction was calculated by an algorithm derived from indicator-dilution theory: ejection fraction = [1 - e(-bd)] X 100, where b = slope of the curve and d = cardiac cycle duration. Linear regression analysis between values of ejection fraction derived by angiography and contrast echo yielded r = 0.73. A second index, based on b and d, was derived by multiple regression analysis. Linear regression analysis of this index and angiographic ejection fraction yielded a correlation of r = 0.87.(ABSTRACT TRUNCATED AT 400 WORDS)

ACC policy statement. Recommended guidelines for training in adult clinical cardiac electrophysiology. Electrophysiology/ Electrocardiography Subcommittee, American College of Cardiology.

Training in clinical cardiac electrophysiology should take place in an Accreditation Council for Graduate Medical Education accredited cardiology program, and the electrophysiology training program itself should be accredited by the Council. Each trainee must be eligible for board certification in Internal Medicine and either eligible for certification in Cardiovascular Diseases or in a program leading to eligibility. Training faculty should be certified in clinical cardiac electrophysiology or demonstrate equivalent credentials. At least two training faculty members are preferred. The faculty must be dedicated to teaching, active in performing or promoting research and must spend a substantial portion of their time in research, teaching and practice of clinical electrophysiology. A curriculum of training should be established. Faculty experts in the related basic sciences should be available and involved in teaching. The institution should have a fully equipped clinical electrophysiology laboratory and complete noninvasive capabilities. A close working relation with a cardiac surgery faculty member skilled in surgical treatment of arrhythmias is required. Training in application of pharmacologic and all current nonpharmacologic therapies, in the outpatient and inpatient setting, is necessary. The clinical exposure must include all facets of arrhythmia diagnosis and treatment and must be quantitatively sufficient to allow the trainee to develop proficiency. The period of training should not be less than one year in addition to the period of cardiology fellowship required by the ABIM for board eligibility. A continuous period of training is preferred.

A low rate of loss of heterozygosity is found at many different loci in childhood B-lineage acute lymphocytic leukemia.

We have carried out a screening for loss of heterozygosity (LOH) in 51 children with B-lineage acute lymphoblastic leukemia (ALL). Forty-six highly polymorphic microsatellite markers located in subtelomeric areas of every chromosome arm were analyzed in each patient. Allelic losses were encountered at 21 of the 46 loci tested (46%). The frequency of LOH at a given locus was usually < 10% and fractional allelic loss, calculated as the ratio of chromosomal arms displaying loss among all informative arms for each patient, ranged from 0.025 to 0.31 (mean, 0.063). This study provides further evidence that deletional events are a major type of genetic alteration found in childhood ALL. The diversity of the loci displaying LOH suggests that, as in solid tumors, numerous tumor suppressor genes are likely to participate in leukemogenesis. However, the overall low frequency of LOH, as well as the absence of microsatellite instability suggest that the genetic instability is lower in childhood ALL than in most of the solid tumors.

[Molecular epidemiology of cystic fibrosis in Tunisia]. / Epidémiologie moléculaire de la mucoviscidose en Tunisie.

Cystic fibrosis is the most frequent autosomal recessive genetic disease in North European population. This pathology seems to not be rare in Tunisia. On another hand, development of molecular biology techniques has largely contributed to implement the study of the different mutations in the CFTR gene where over 1,300 mutations were reported. Herein, we describe the strategy used to detect molecular defects responsible of cystic fibrosis on 390 children (383 families) in Tunisian population. Several techniques were performed for genotype diagnosis: DNA extraction was from peripheral blood. Polymerase chain reaction (PCR) and polyacylamide gel electrophoresis, and reverse dot blot procedures were used to detect known point mutations. Denaturant gradient gel electrophoresis (DGGE) were used in a next step searching for the unknown point mutations that are later identified by automated sequencing on ABIprism 310. This strategy allowed us to detect 17 different mutations located on the different exons of the CFTR gene. The most frequent was the F508del (50.74%) followed by three other mutations (G542X, W1282X and N1303K) known to be common in the Mediterranean area. For mutations (T665S, 2766 del8, F1166C, L1043R) were exclusively found, up to now, in the Tunisian population. Our results permitted to establish cystic fibrosis mutations and their distribution in Tunisia and to implement an appropriate prevention program of these diseases through the genetic council and prenatal diagnosis.

Genotype determination at the survival motor neuron locus in a normal population and SMA carriers using competitive PCR and primer extension.

Precise quantitation of SMN1 copy number is of great interest in many clinical applications such as direct detection of SMA carriers or detection of an SMA-affected patient with a hemizygous deletion of the SMN1 gene. We describe a method that combines two independent nonradioactive PCR assays: determination of the relative ratio of the SMN1 and SMN2 genes using a primer extension assay and of the total SMN copy number using competitive PCR. Consistency of the results of two independent approaches ensures the reliability of the deduced genotype and thus avoids false interpretation of borderline results that can occur in quantitative assays. In all, 135 subjects were tested, including 91 normal controls and 44 SMA-affected children or SMA carriers. Two main genotypes were observed in controls: 2T/2C (45%) and 2T/1C (32%). A wide variability at the SMN locus is observed with nine different genotypes and up to six SMN genes. SMA carriers showed three frequent genotypes, 1T/2C (50%), 1T/3C (29%), and 1T/1C (18%). Normal chromosomes with two SMN1 genes per chromosome are not infrequent and thus, about 3% of SMA carriers are not detected using SMN1 copy number quantitation. Finally, as this method does not detect point mutations (4% of SMN1 gene mutations), reliability ranges from 93% to 100% depending on data available from the propositus.

Influence of thyroid status on hemoglobin A2 expression.

We studied the electrophoretic pattern of hemoglobin (Hb) and red blood cell indices in 128 women divided into four groups: group I, 36 nonanemic hyperthyroid women, divided in two subgroups: 36 with untreated hyperthyroidism (subgroup IA) and 9 made euthyroid by antithyroid drug therapy (subgroup IB); group II, 12 nonanemic women with untreated hypothyroidism; group III, 30 women known to be heterozygous for beta-thalassemia; and group IV, 50 healthy women. The mean (+/- SEM) HbA2 level was higher (P less than 0.001) in subgroup IA (3.21 +/- 0.06%) than in subgroup IB (2.42 +/- 0.09%) and group IV (2.48 +/- 0.04%), but lower (P less than 0.001) than in group III (5.26 +/- 0.12%). The mean HbA2 level was lower (P less than 0.001) in group II (1.99 +/- 0.08%) than in group IV. Hb fetal was detectable in eight patients of subgroup IA and undetectable in subgroup IB and groups II and IV. The mean cellular volume was lower (P less than 0.001) in subgroup IA than in other nonanemic groups. The mean cellular volume was higher (P less than 0.001) in group II than in group IV. Follow-up of nine patients who became euthyroid with treatment showed the normalization of these erythrocyte parameters. These results suggest that thyroid hormones can modulate the synthesis of delta- and gamma-globin chains.

Distribution of CFTR mutations in cystic fibrosis patients of Tunisian origin: identification of two novel mutations.

Cystic fibrosis (CF), the most common lethal genetic disease in the Caucasian population, is caused by mutations in the CF transmembrane conductance regulator gene (CFTR). More than 500 molecular defects have been reported to date. The distribution of these mutations is both heterogeneous and population related. In Mediterranean populations, 20-30% of CF alleles remain unidentified. We have studied a sample of 39 CF patients of Tunisian origin and have used a GC clamp DGGE assay to scan the CFTR gene. Two novel mutations have been found, but we have been unsuccessful in finding any mutation in 40% of these alleles. These results suggest that, in this Mediterranean population, additional mutations may lie elsewhere in the promoter region or in introns not yet analyzed.

N219Y, a new frequent mutation among mut(degree) forms of methylmalonic acidemia in Caucasian patients.

Mutations in the MUT locus encoding for the methylmalonyl-CoA mutase (MCM) apoenzyme are responsible for the mut forms of methylmalonic acidemia (MMA). To date, 49 different mutations have been identified in mut MMA. Only two frequent mutations have been reported in the Japanese population and in African-Americans. Here we report a new missense mutation N219Y (731 A-->T) which we found in five unrelated families of French and Turkish descent. All the patients exhibited a severe mut(degree) phenotype and three of them were homozygotes for N219Y. Direct involvement of the mutation in the loss of enzyme activity was demonstrated by mutagenesis and transient expression study. Mapping of the mutation onto a three-dimensional model of human MCM constructed by homology with the Propionibacterium shermanii enzyme shows that it lies in a highly conserved secondary structure motif and might suggest impaired folding and/or poor stability compatible with the mut(degree) phenotype. Finally, a 1% N219Y carrier frequency was observed in a French anonymous control population. Thus, N219Y is the first frequent mut mutation to be reported in the Caucasian population.

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.

Genetic polymorphism of the mannose-binding protein gene in children with sickle cell disease: identification of three new variant alleles and relationship to infections.

Mannose-binding protein (MBP) is a serum lectin that participates in the innate immune response. MBP deficiency may constitute a risk factor in the development of infections. Three MBP structural variants have been identified with a dominant effect on MBP serum concentration. Similarly, polymorphisms in the promoter of the corresponding gene (HSMBP1B) have been related to variations of MBP concentration in serum. Children with sickle cell disease (SCD) have an increased susceptibility to infections with encapsulated organisms resulting in meningitis, septicaemia, and osteomyelitis. We have investigated the HSMBP1B genotype in 242 children with SCD living in Paris. Apart from the known variant alleles, we identified three novel ones and report their distribution in our sample population. In addition, we found rather unexpectedly an increased frequency of the variant alleles in patients who had not suffered severe infections.

Complete sequence of the major outer membrane protein-encoding gene of Chlamydia trachomatis serovar Da.

The complete nucleotide sequence of the gene omp1 encoding the major outer membrane protein (MOMP) of Chlamydia trachomatis serovar Da was determined following amplification by the polymerase chain reaction. The most closely related complete sequence published to date is that encoding the C. trachomatis L1 MOMP. When the L1 and Da MOMP deduced amino acid (aa) sequences were compared, 16 single-aa differences located mostly in the variable domains I, II, and IV were detected. These regions contain the B-cell epitopes. Additional differences were found in the constant domains I and II, thought to participate in the T-cell response.

A simple strategy to amplify specifically the HLA-DQ beta gene region with genomic DNA as template.

The nature of codon 57 in the HLA-DQ beta gene was recently reported as a potential marker of genetic susceptibility to insulin-dependent diabetes mellitus. When exploring the relevance of this marker by using genomic DNA amplification, we encountered difficulties resulting from the coamplification of the homologous DX beta region. A simple strategy is proposed to amplify the DQ beta region exclusively. It involves the preliminary digestion of genomic DNA with a restriction enzyme which cleaves DX beta specifically, leaving intact the DQ beta sequence. The amplified material is suitable for dot blot analysis and restriction enzyme digestion. This strategy is of general interest when homologous sequences impair the specificity of enzymatic DNA amplification.

Ca++ binding properties of human prothrombin.

The binding of Ca++ to human prothrombin has been investigated by equilibrium dialysis. The protein exhibited a positive cooperativity phenomenon for the first three Ca++ bound. Eleven to twelve Ca++ binding sites have been found. They could be differentiated in terms of two classes of sites with respect to their Ca++ affinity: 5 strong binding sites (log Kassoc = 3.9) and 7 weak binding sites (log Kassoc = 2.9). We attempted to determine the Hill coefficient of the strong binding sites responsible for cooperativity. Results have been compared to data previously reported for bovine prothrombin.