Genetic model for observed distributions of proportions of haemoglobin in sickle-cell trait

Haemoglobin D Punjab. Interaction with alpha thalassaemia and diagnosis by gene mapping

A family which illustrates the inheritance of Hb D Punjab (a beta globin chain variant) and alpha thalassaemia is described. Interaction between Hb D Punjab and alpha thalassaemia is observed since levels of Hb D vary according to the number of alpha globin genes deleted. The technique of gene mapping has been utilised in the current study to provide definitive evidence of alpha thalassaemia and also demonstrates a novel way to identify Hb D Punjab.

Molecular and cellular pathogenesis of hemoglobin SC disease

Solution and cell studies were performed to ascertain why individuals with hemoglobin (Hb) SC have disease whereas those with Hb AS do not. The polymerization of deoxygenated mixtures containing sickle cell Hb (Hb S; alpha 2 beta 2(6)Glu leads to Val) and Hb C (alpha 2 beta 2(6)Glu leads to Lys) was investigated by measurements of delay times and solubilities. In mixtures containing more than 40% Hb S, polymerization takes place by the same mechanism as in solutions of Hb S alone, with no evidence for independent crystallization of Hb C. A detailed comparison of Hb S/Hb C and Hb S/Hb A mixtures with identical concentrations and proportions of Hb S show that there is no significant difference in the tendency of Hb C and Hb A to copolymerize with Hb S. In 50:50 Hb S/Hb C mixtures, polymerization is about 15 times more rapid than in 40:60 Hb S/Hb A mixtures at the same total Hb concentration. Measurements on density-fractionated erythrocytes show that SC cells contain a higher total Hb concentration and a more uniform distribution of reticulocytes compared to normal (AA) or sickle trait (AS) cells. The concentration distribution for C trait (AC) cells is much closer to that of SC cells than to AS or AA cells. It appears, therefore, that the presence of Hb C results in the SC cell beginning its life with an abnormally high Hb concentration. From these findings we conclude that both the larger proportion of Hb S and the higher intracellular Hb concentration contribute to the pathogenesis of Hb SC disease.

Hemoglobin E diseases: hematological, analytical, and biosynthetic studies in homozygotes and double heterozygotes for alpha-thalassemia

Two families with Hb E diseases are described. In the Laotian family S, three homozygous Hb E were found. In the Vietnamese family H, double heterozygous Hb E-alpha-thalassemia-2 and Hb E-Hb H diseases were found. Anemia or hemolysis was absent in Hb E carriers, unless complicated by iron deficiency, the presence of severe alpha-thalassemia gene (Hb H disease), or oxidative drug (paraaminosalicylic acid). Moreover, iron deficiency or concurrent alpha-thalassemia genes resulted in a decreased amount of Hb E in its heterozygous carriers. Mild microcytosis and hypochromia were observed in Hb E heterozygotes, whereas the microcytosis and hypochromia were more pronounced in Hb E homozygotes. Globin chain synthesis studies yielded unbalanced alpha/non-alpha ratios in both heterozygotes and homozygotes (average ratios were 1.13 and 1.56, respectively). The unbalanced biosynthetic ratios with microcytosis and hypochromia in Hb E carriers represented a beta-thalassemia phenotype, which could be a result of reduced synthesis of beta E-globin mRNA, as suggested by recent hybridization studies.

The laboratory evaluation of microcytic red blood cells

Microcytic red blood cell states are common clinical problems in both adult and pediatric age groups. The recent widespread availability of electronic blood cell counters for performing routine blood counts has increased the detection of microcytic red blood cells. Physicians must workup both symptomatic and asymptomatic patients with microcytic red blood cells before they can initiate proper therapy and/or counseling. The purpose of this review is threefold: (1) to discuss the causes of microcytic red blood cells in terms of disorders of decreased heme production vs. disorders of decreased globin production, (2) to review the clinical laboratory tests useful in differentiating microcytic red blood cell states, and (3) to present a practical approach for the laboratory workup of microcytic red blood cells.

Two different molecular organizations account for the single alpha-globin gene of the alpha-thalassemia-2 genotype

The alpha-thalassemia-2 (alpha-thal-2) genotype or mild alpha-thalassemia gene consists of a single structural alpha-globin gene on the chromosome that normally bears two alpha-globin genes. We used blot hybridization to investigate variation in the molecular organization of this genotype and to determine the distributions of these variations in the world population. Two different patterns of gene organization responsible for the alpha-thal-2 genotype were found: the first was the result of a 4.2-kilobase pair deletion involving the normal 5' alpha-globin gene (leftward deletion alpha-thal-2 genotype), and the second probably the result of a crossover deletion of a DNA fragment bridging the two normal alpha-globin genes (rightward deletion alpha-thal-2- genotype). The rightward deletion was found in all 9 Black subjects, all 8 Mediterranean subjects, and 4 of 13 Chinese subjects. The leftward deletion was found in four and the nondeletion alpha-thalassemia lesion was found in five of the nine remaining Chinese subjects. It is likely that these deletions are related to specific DNA sequences that determine DNA recombinational events.

Genetics of cat hemoglobins: a quantitative polymorphism

Blood samples from domestic cats, representing the parents (26) and offspring (91) from 33 matings, were analyzed to determine the proportions of hemoglobins A and B. Evidence is presented that the proportions of the two hemoglobins are genetically determined and that cats may be divided into three groups on the basis of this characteristic. Family data and Hardy-Weinberg analysis support the hypothesis that the three groups represent the possible combinations of an allelic gene pair. In an attempt to explain the observed phenotypic differences, possible points of action of this gene pair are discussed, including effects on rates of synthesis or epigenetic modification of globin chains.

Sickle cell anemia and trait in southern India: further studies

Population surveys and family studies among 568 members of nine ethnic groups in southern India identified 15 homozygotes for sickle hemoglobin (HbS)who had mild clinical and hematological manifestations with high levels of fetal hemoglobin (mean=20%, range 8-36%) in a heterogeneous red cell distribution. In one family, the heterozygous mother had a hemoglobin pattern consistent with a form of the heterocellular hereditary persistence of fetal hemoglobin. Sickle cell trait was found in 153(27%) of those studied. Chromatographic quantitation of the hemoglobin fractions in these heterozygotes showed a trimodal distribution of the proportion of HB Sexplicable by a genetic model postulating the presence of genotypes with two (-alpha/-alpha), three (-alpha/alpha alpha) and four (alpha alpha/alpha alpha) active alpha-globin genes. Globin synthesis studies in four heterozygotes believed to have two active alpha-globin genes demonstrated an alpha/non-alpha total activity ratio (0.57) consistent with this model.