A case of the abnormal hemoglobin C.
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The authors studied 31 cases of coronary artery disease with normal or minimally diseases coronary arteries in black Africans, 29.8% of 104 coronary patients undergoing coronary angiography in this series. These 31 cases comprised 16 cases of infarction, 10 cases of angina, 3 ventricular aneurysms and 2 cases of silent ischemia in diabetic patients. Twenty-five patients were men (80.6%). There were 6 women (19.3%) two of whom presented in the post-partum period. The average age of these patients was 45 years (males: 47.7 years; females: 41.8 years). The following risk factors were noted: smoking (60%), hypertension (25.8%), obesity (29%), diabetes (12.9%), serum cholesterol (average 2.15 g/l), serum triglycerides (average 1.25 g/l). The risk index per patient was 1.29. In comparison with coronary patients with angiographic coronary lesions (n = 73), the patients with normal angiography were significantly younger, comprised more females and had fewer risk factors (especially hypertension and diabetes), though this was not statistically significant. The prevalence of inaugural infarction was 81.2% in the cases of infarction with normal coronary arteries. These infarcts may be complicated by ventricular aneurysm formation. Spontaneous spasm was observed in 3 out of 31 patients (9.6%) at coronary angiography. A provocative test was performed in only 2 cases and 1 was positive. This deserves further study and may have therapeutic implications. The authors emphasise the high incidence of hemoglobin S or C traits (57.1%). These heterozygotic hemoglobinopathies could be a risk factor in these coronary patients with normal coronary angiography.
Thalassemias are a group of genetic disorders caused by unbalanced synthesis of alpha- and non-alpha chains of globins due to impaired globin genes. Clinical characteristics of the thalassemias are ineffective erythropoiesis and hemolytic anemia with microcytic-hypochromic erythrocytes. Surplus polypeptide chain synthesized by normal globin gene causes harmful effects to skeleton proteins of erythrocyte membrane, such as spectrin, ankirin and 4.1 protein, via a few different ways and normal integrity of membrane is disturbed. Basic mechanism of pathophysiology of thalassemias have been made clear but many problems remain to be overcame in clinical practice. Several methodological improvements in diagnosis have been coming out using DNA amplification technique and applied to prenatal diagnosis and mass-screening of thalassemias. In therapeutic methods, little improvement has been observed for last decade since introduction of bone marrow transplantation.
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On routine electrophoretic analyses on filter paper and starch gel in an alkaline or neutral medium, no abnormal hemoglobin fractions were found in the blood of 600 newborn infants or their mothers. Trace amounts of hemoglobin Barts were noted in many of the blood samples from newborns when the starch gels (phosphate buffer pH 7.0) were stained with a benzidine/H(2)O(2) reagent. In one infant, precocious cessation of synthesis of hemoglobin F was postulated to account for the small amounts of this hemoglobin found in a cord-blood specimen. Analysis of 15,000 blood samples from adults revealed two instances in which the hemoglobin F level was 20 and 35%, respectively. The former was attributed to a hereditary persistence of hemoglobin F, while the latter was associated with acute leukemia.In an addendum, the finding of an infant with an abnormal hemoglobin variant, resembling in many of its properties hemoglobin F Texas, is reported.
A survey of nearly 250,000 citizens of Georgia and South Carolina conducted during the past twenty years has led to the detection of over 40 abnormal hemoglobins and several additional hemoglobinopathies. The presence of some of these hemoglobin abnormalities cause (severe) clinical symptoms but others remain undetected unless a specific search is initiated. The incidence of Hb S varies slightly among the populations of different areas, and appears to be the highest in the coastal counties of Georgia and South Carolina. A survey of over 17,000 persons of mainly high school and college age has shown that a significant number of cases with clinically significant hemoglobinopathies will remain undetected unless such surveys are actively promoted.
Hemoglobin E is very common in parts of Southeast Asia. The possible malaria protective effects of this and other inherited hemoglobin abnormalities prevalent in Thailand were assessed in a mixed erythrocyte invasion assay. In vitro, starting at 1% parasitemia, Plasmodium falciparum preferentially invaded normal (HbAA) compared to abnormal hemoglobin (HbH, AE, EE, HCS, beta-thalassemia E) red cells (HRBCs). The median (range) ratio of parasitization of HRBCs (n = 109) compared to the controls of different major blood groups was 0.40 (0.08, 0.98), less than half that of the normal red cells (NRBCs) compared to their controls 0.88 (0.53, 1.4; P =.001). The median (range) parasitemia in the HRBCs was 2% (0.1%-9%) compared to 5.2% (1.2%-16.3%) in the NRBCs (P =.001). The proportion of the RBC population that is susceptible to malaria parasite invasion can be described by a selectivity index (SI; observed number of multiply invaded RBCs/number predicted). The heterozygote AE cells differed markedly from all the other cells tested with invasion restricted to approximately 25% of the RBCs; the median (range) SI was 3.8 (1-15) compared with 0.75 (0.1-0.9) for EE RBCs (P <.01). Despite their microcytosis, AE cells are functionally relatively normal in contrast to the RBCs from the other hemoglobinopathies studied. These findings suggest that HbAE erythrocytes have an unidentified membrane abnormality that renders the majority of the RBC population relatively resistant to invasion by P falciparum. This would not protect from uncomplicated malaria infections but would prevent the development of heavy parasite burdens and is consistent with the "Haldane" hypothesis of heterozygote protection against severe malaria for hemoglobin E.
Screening of the university students for hemoglobinopathies detected 153 patients with various hemoglobin abnormalities; 69 with Hb AS, 3 with Hb S-beta-thalassemia, 4 with Hb S-alpha-thalassemia, 3 with hb SC, 1 with Hb SK, 1 with Hb CC, 38 with Hb AC, 1 with Hb A O Arab, 4 with Hb EE, 25 with Hb AE, 1 with Hb AD, 1 with Hb AI, 1 with beta-thalassemia major, and 1 with beta-thalassemia minor. The most grave disease was observed in a child with Hb S-beta-thalassemia and in a youth with beta-thalassemia major. The patterns of Hb SC disease varied. The majority of heterozygote carriers of Hb S, Hb C, Hb E, etc. were healthy. A total of 7000 students were screened by express electrophoresis on cellulose acetate films. more than 400 subjects with abnormal hemoglobins were detected, the most numerous of which were heterozygote carriers of Hb S (Hb AS).
Abnormal human hemoglobins (HBs) with amino acid substitutions in the alpha 1 beta 2 interface have very high oxygen affinity and greatly reduced cooperativity in O2 binding compared to normal human Hb. In such abnormal Hbs with mutations at position beta 99, the intersubunit hydrogen bonds between Asp-beta 99 and Tyr-alpha 42 and between Asp-beta 99 and Asn-alpha 97 are broken, thus destabilizing the deoxyquaternary structure of these Hbs. A molecular dynamics method has been used to design compensatory amino acid substitutions in these Hbs that can restore their allosteric properties. We have designed a compensatory mutation in a naturally occurring mutant Hb, Hb Kempsey (Asp-beta 99-->Asn), and have produced it using our Escherichia coli expression plasmid pHE2. We have determined the O2 binding properties of this recombinant double mutant Hb, Hb(Asp-beta 99-->Asn and Tyr-alpha 42-->Asp) and have used 1H NMR spectroscopy to investigate the tertiary structures around the heme groups and the quaternary structure in the alpha 1 beta 2 subunit interface. Our results clearly show that the Tyr-alpha 42-->Asp replacement can substantially compensate for the functional defect of Hb Kempsey caused by the Asp-beta 99-->Asn substitution. The structural and functional information derived from this recombinant Hb provides insights into the structural basis of allosterism and the design of compensatory amino acid substitutions to restore the functional properties of other abnormal HBs associated with hemoglobinopathies.
A healthy Thai male was found to have an abnormal hemoglobin moving faster than Hb A in starch-gel electrophoresis, in addition to the normal hemoglobin constituents. The abnormal hemoglobin constituted 28% of the whole hemoglobin. The subject was asymptomatic and had normal hematologic findings. Structural characterization revealed that the amino acid substitution was alpha 56 Lys leads to Thr. This variant has never been described previously and it is named Hb Thailand.
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