-thalassemia in the American Negro

Haemoglobin-H disease presenting with microcytic hypochromic anaemia in an 81 year old woman

Over an 11 year period, the diagnosis of haemoglobin-H (Hb-H) disease was missed in a Caucasian woman of British stock who first presented with microcytic hypochromic anaemia at the age of 81. The diagnosis was confirmed at the age of 92, when the typical inclusions of Hb-H disease were demonstrated in erythrocytes stained with brilliant cresyl blue, and the presence of Hb-H was documented by haemoglobin electrophoresis. She subsequently developed biliary obstruction due either to an inflammatory polyp associated with choledocholithiasis or ampullary carcinoma.

Linkage of alpha G-Philadelphia to alpha-thalassemia in African-Americans

We have studied the inheritance of the alpha-chain hemoglobin variant Hb G-Philadelphia (alpha 2(68 Asn leads to Lys)Beta 2) in two African-American families. Expression of the alpha-globin loci was monitored by the percentage of Hb G in these individuals. The variant represented approximately 33% of the total adult hemoglobin in some and 50% in others. alpha-Globin gene fragments were analyzed by using restricton endonucleases that cleave outside (EcoRI), within (HindIII), and between (Bgl II) the normal duplicated alpha-globin loci (alpha alpha/alpha alpha). Individuals having 33% variant lack one functioning alpha gene (alpha G/alpha alpha); those with 50% variant lack two genes, one missing on each chromosome (alpha G/alpha). Inheritance of alpha G was therefore linked to that of a chromosome with only one functional alpha-globin gene locus. This locus is probably the result of a nonhomologous crossover. Our results also suggest equal expression of the alpha-globin loci in humans because the percentages of the variant could be explained solely on the basis of the total number of alpha genes present. The percentages of Hb G as well as other hematologic data all were consistent with the number of alpha-globin genes identified by restriction endonuclease mapping. Gene mapping yields a more precise determination of the number of alpha-globin genes than does study of globin synthesis.

Determination of alpha thalassaemia phenotypes by messenger RNA analysis

The possibility of using alpha/beta globin messenger RNA (mRNA) ratios to distinguish between the carrier states for different forms of alpha thalassaemia has been explored. Alpha/beta globin mRNA ratios were determined in the red cells of a series of normal individuals and in members of four Cypriot families, one Thai and one Chinese family in which at least one person has haemoglobin H disease. It was found that there was a clear distinction in the ratios between normals, alpha thalassaemia 1 carriers, alpha thalassaemia 2 carriers, and those with haemoglobin H disease. This method should be a valuable addition to haematological analysis, haemoglobin synthesis and restriction mapping of DNA for the further elucidation of the genetics of alpha thalassaemia.

Clinical features of thalassemia

The thalassemia syndromes are an important group of diseases in childhood, frequently encountered in many ethnic groups worldwide. Heterozygotes are frequently misdiagnosed as having iron deficiency anemia, and the more severely affected homozygotes present major problems in management. Advances in prenatal diagnosis offer hope for prevention, while progress in transfusion therapy, accuracy of prediction of value of splenectomy, and chelation therapy offer improved quality and, perhaps, duration of life.

Alpha thalassaemia in Sicily: haematological and biosynthetic studies

Eight Sicilian patients with Hb H disease and their families have been studied. The standard haematological tests and the alpha/beta chain synthesis ratios showed significantly different results in the patients with Hb H disease as compared with alpha thalassaemia carriers, except for Hb A2 values. There was no significant difference in the mean RBC, MCV, Hb A2, Hb A1 and Hb F of alpha thalassaemia carriers compared with normal controls. On the contrary significant difference was found between the mean alpha/beta chain synthesis ratio of alpha thalassaemia carriers and that of the normal controls; however, the extensive overlapping of alpha/beta values between these two conditions make this parameter insufficiently discriminant. No correlation was found between MCV, MCH, RBC and alpha/beta chain synthesis ratio in patients with alpha thalassaemia trait, suggesting that the ratio cannot be used to distinguish between carriers of a mild gene ('silent' carrier) and carriers of the more severe alpha thalassaemia gene. A possible genetic model for alpha thalassaemia in Sicily is presented.

Modification of hemoglobin H disease by sickle trait

The rarity of hemoglobin (Hb) H disease in combination with sickle trait may be due in part to the absence of actual Hb H in individuals who, nonetheless, have inherited the deletion of three alpha-globin genes. We describe here a boy with persistent microcytic, hypochromic anemia despite adequate iron stores, who exhibited splenomegaly with a normal reticulocyte count and only rare inclusions in circulating erythrocytes. Starch gel electrophoresis and isoelectric focusing at age 5 yr showed 21% Hb S, persistent Hb Bart's, but no Hb H. Recticulocyte alpha/non-alpha globin chain synthesis ratio was 0.58 at age 5. The mother (Asian) had laboratory evidence of alpha-thalassemia trait and the father (Black) had sickle trait. The nature of alpha-thalassemia in this patient was investigated both by liquid hybridization and by the Southern method of gene mapping, in which DNA is digested with restriction endonucleases and the DNA fragments that contained the alpha-globin structural gene identified by hybridization with complementary DNA. The patient had only one alpha-globin structural gene, located in a DNA fragment shorter than that found in normal or alpha-thalassemia trait individuals, but similar to that present in other patients with Hb H disease. Morphologic studies of bone marrow by light and electron microscopy revealed erythroid hyperplasia with inclusions in polychromatic and orthochromatic erythroblasts, suggesting early precipitation of an unstable hemoglobin. The lack of demonstrable Hb H may be the result of both diminished amounts of beta(A) available for Hb H formation (since one beta-globin gene is beta(S)) and the greater affinity of alpha-chains for beta(A) than beta(S)-globin chains leading to the formation of relatively more Hb A than Hb S. The presence of a beta(S) gene may thus modify the usual clinical expression of Hb H disease.

Alpha-thalassemia in blacks is due to gene deletion

We used molecular hybridization to test if alpha-thalassemia is due to gene deletion in the black. In 10 families with clinically well-defined alpha-thalassemia-1 (alpha-thal-1), hydribization of alpha-globin cDNA was reduced to the same level as that found in Asians with alpha-thal-1, where two of the four normally present alpha-globin genes are deleted. A black child with hemoglobin H (Hb H) disease also has three globin genes deleted, as do Asian patients with Hb H disease. We conclude that alpha-thalassemia in the black is most commonly due to gene deletion.

The molecular basis of alpha-thalassemias: frequent occurrence of dysfunctional alpha loci among non-Asians with Hb H disease

Study of Asians has previously indicated that deletion of alpha-globin structural genes is the predominant lesion in alpha-thalassemias and that Hb H disease occurs when three of four normal alpha loci per cell are deleted. To test the generality of this model, Hb H disease DNAs of both Asian and non-Asian origin were analyzed by restriction endonuclease mapping using the technique of Southern (1975). Whereas in normal DNA, alpha sequences are present in a single Eco Rl fragment of cellular DNA approximately 22.5 kb long, fragments of 22.5, 20 and 2.6 kb were found in various Hb H disease DNAs. The 20 kb Eco Rl fragment alone, in which a single alpha-globin structural locus resides, was found in Asian Hb H disease DNA. This finding is consistent with the deletion model of alpha-thalassemia. In contrast, seven of eight non-Asian Hb H disease DNAs displayed a more complex molecular composition. The fragment patterns observed were 22.5 kb alone, 22.5 plus 2.6 kb, 20 plus 2.6 kb and 20 kb alone. Non-Asian Hb H disease DNAs contained one, two or three alpha loci per cell in contrast to the one locus predicted by the simple deletion model of alpha-thalassemia. The data are best explained by the existence of defective alpha loci in certain individuals with alpha-thalassemia, particularly outside the Asian population. Restriction mapping of the 20 kb Eco Rl fragment found in Asian and some non-Asian Hb H disease DNAs demonstrated a striking similarity in the placement of restriction sites about the single alpha gene compared with sites about the two genes in the 22.5 kb Eco Rl fragment seen in normal DNA. These data are consistent with origin of the 20 kb fragment from the 22.5 kb normal Eco Rl fragment by either unequal crossing-over or a deletion event. The molecular heterogeneity and frequent occurrence of defective alpha loci in non-Asian Hb H disease DNAs described here may explain, in part, the clinical heterogeneity of alpha-thalassemias and the absence of the homozygous deletion state (hydrops fetalis) in non-Asians. Further study of cellular DNA fragments containing the defective alpha loci identified in this work may indicate the types of specific mutations responsible for abnormal globin gene expression and complement similar studies on abnormal beta genes in beta-thalassemias.

Alpha thalassaemia in American blacks: a study of a family with five cases of haemoglobin H disease

Five cases of HbH disease were discovered in a large family of American Blacks. Anaemia was mild with PCV ranging from 0.275 to 0.405. The amount of HbH was 2--6%. Studies of haemoglobin synthesis in peripheral blood reticulocytes demonstrated marked deficits in alpha globin production with an average alpha/beta ratio of 0.31 (range 0.22--0.36). Eighteen additional family members had evidence of thalassaemia trait and were provisionally classified as either alpha-thal-1 (average MCV 65.2 fl; range 59--70) or alpha-thal-2 (average MCV 79.6 fl; range 74--88). A subject with altha-thal-1 trait had an alpha/beta ratio of 0.56; the average for five cases of alpha-thal-2 was 0.73. One other family member was thought to be homozygous for alpha-thal-2 trait and exhibited an MCV of 65 fl with an alpha/beta ratio of 0.5. These data reconfirm that in Blacks with alpha thalassaemia the proportion of HbH is lower and the severity of anaemia is less than in certain other racial groups, e.g. Southeast Asians. However, the degree of hypochromia and microcytosis and the imbalance in alpha and beta globin synthesis appear to be similar in Blacks and other races. These results suggest that the milder clinical course of HbH disease in Blacks is not a result of greater alpha globin production in that population of thalassaemics.

Thalassaemia of intermediate severity resulting from the interaction between alpha- and beta-thalassaemia

A Sicilian family is described in which the alpha-thalassaemia gene is interacting in several members with beta-thalassaemia resulting in a balanced alpha/beta chain production ratio. In one patient, affected by homozygous beta-thalassaemia, the presence of alpha-thalassaemia resulted in a less severe clinical expression of the disease, less marked imbalance in the alpha/non-alpha ratio, and a lower level of HbF. Further studies of haemoglobin synthesis are needed to clarify the complex genetic picture that results from the interaction of different forms of thalassaemia.

Haemoglobin H disease in 2 Filipino families

Haemoglobin H disease is described in successive generations of 2 Filipino families. The condition was asymptomatic. The inheritance pattern of haemoglobin H disease in these families appeared to be like that described for Thais.

Prenatal diagnosis of hemoglobinopathies

Techniques are currently available at a few specialized centers for the antenatal detection of hemoglobinopathies such as beta thalassemia and sickle cell anemia. The risks are not yet clearly defined, but it seems reasonable to suggest that about 90 per cent of families may obtain useful information about the genotype of their fetus. Obtaining fetal blood as well as analyzing the sample requires considerable experience and skill. These factors continue to limit the availability of this procedure.

Hemoglobin H disease in Sardinia: phenotypic and genetic observations

In this study the clinical and hematological characteristics, the transmission pattern and the relative rates of globin chain synthesis were determined in the members of four Sardinian families with 14 patients affected by hemoglobin H disease. The severity of hemoglobin H disease in Sardinian subjects shows a high degree of variability. Clinically it usually appears intermediate between the hemoglobin H disease found in Oriental and Negro populations. The alpha/beta specific activity ratio was 0.42 +/- 0.10 indicating an analogous biochemical defect like that described in the Chinese. On the basis of hematological data and alpha/beta ratio, the genetics of hemoglobin H disease in Sardinians seem to follow a pattern similar to that observed in Orientals: one parent showing alpha-thalassemia-1 trait and the other alpha-thalassemia-2 trait. Parent offspring transmission of hemoglobin H disease did occur in 2 out of 6 hemoglobin H matings with spouses carrying the alpha-thalassemia-1 gene. This observation indicates either a high frequency of alpha-thalassemia trait in Sardinians or a high incidence of inbreeding. In one family the mating of a patient with hemoglobin H disease and a normal person produces 6/6 offspring with alpha-thalassemia-1. The genetic implications of this transmission pattern are discussed.

Alpha-thalassemia

The current concepts of alpha-thalassemia including incidence, genetics, clinical spectrum and diagnosis are reviewed. Speculation concerning clinical application of the molecular biology of alpha-thalassemia is also presented.

Studies of the proporation and synthesis of haemoblogin C Philadelphia in red cells of heterozygotes, a homozygote, and a heterozygote for both haemoglobin G and alpha thalassaemia

The proportion of Hb G Philadelphia (alpha68-Asn leads to Lys) in heterozygotes has been found to have a well-defined bimodal distribution around means of 33% and 46% Hb G. microcytosis and hypochromia are consistently associated with the latter group, who also have a decreased ratio of alpha/beta-chain synthesis in the peripheral blood, but these characters are not linked to the Hb-Galpha gene, because a parent with microcytosis and 46% Hb Galpha may have offspring with 33% Hb G without significant microcytosis. In one family a subject with Hb G and Hb G2 but no Hb A or Hb A2 is presumably a homozygote for alphaG. This subject has microcytosis and a decreased ratio of alpha/beta chain synthesis. In another family a subject with Hbs H, G and G2 but without Hbs A or A2 is heterozygous for both Hb G and alpha thalassaemia I. These findings are compatible with the hypothesis that the alphaG mutation occurs on a chromosome with only a single alpha-chain locus and that the expression in heterozygotes as 46% or 33% Hb G is determined by the homologous chromosome in trans having either one or two normal alphaA genes respectively. The significance of this polymorphism for chromosomes carrying alpha-chain genes is discussed.

Trimodality in the proportion of hemoglobin G Philadelphia in heterozygotes: evidence for heterogeneity in the number of human alpha chain loci

The extent of variability in the number of human hemoglobin (Hb) alpha chain loci has not yet been conclusively determined. There is evidence that in some populations individuals may possess two alpha-chain loci, while in other populations only one locus is present. Electrophoresis of peripheral blood from 53 heterozygotes for Hb G Philadelphia (alpha 68 Asn leads to Lys) revealed that the proportion of Hb G is trimodally distributed, with modes at approximately 20, 30, and 40% Hb G. Familial, hematologic, and statistical studies suggest that hte proportion of Hb G is not random but is genetically controlled and inversely correlated with mean cell volume. Two alternative genetic models are proposed to explain these findings: one assums alpha-thalassemia, while the other postulates variability in the number of alpha-chain loci in the American Black population. Biosynthetic studies of blood from 15 subjects revealed balanced synthesis of alpha and beta globin chains in heterozygotes from all three classes, strongly supporting variable gene dosage rather than alpha-thalassemia as the mechanism underlying the observed trimodality in the proportion of Hb G. Incompatibilities between out results and current concepts of alpha-thalassemia are discussed in the context of differences between Black compared with Oriental and Italian forms of Hb H disease.

Unbalanced globin chain synthesis in erythroid precursor cells of heterozygous alpha-thalassaemia

Globin biosynthesis was studied in both erythroid precursors and reticulocytes of three individuals with heterozygous alpha-thalassaemia. In contrast to the finding of equal or nearly equal alpha and beta chain synthesis in the marrow of patients with heterozygous beta-thalassaemia previously examined, our studies showed equal degrees of unbalanced globin synthesis in both reticulocytes and nucleated-erythroid cells of alpha-thalassaemia heterozygotes. Greater stability and less susceptibility to proteolysis of the excess beta-chain formed in alpha-thalassaemia may explain our findings.

The interaction of alpha-thalassaemia and haemoglobin G Philadelphia

An American Negro woman was found to have HbH disease in association with HbG Philadelphia (alpha68-asn leads to lys). Starch gel electrophoresis failed to reveal the presence of any HbA or HbA2 and studies of globin chain synthesis indicated absence of alphaA production. The alphaG/beta synthesis ratio was 0.63. The woman's son and her two half-sibs had alpha-thalassaemia trait with no HbH and alpha/beta synthesis ratios of 0.84, 0.84 and 0.76. The data indicate that there is no functioning alphaA gene linked to the alphaG gene. The absence of alphaA synthesis by the propositus also indicates that the alpha-thalssaemia gene trans to the alphaG gene completely suppresses alpha chain production, the first evidence for such a gene in Negroes.

Neonatal screening for haemoglobinopathy. Results in 7691 Manchester newborns

Over a period of one year the blood samples collected for phenylketonuria testing from 7691 Manchester newborns were screened by haemoglobin electrophoresis. An abnormality was detected in 47 (0-61%) of the babies. No cases of homozygous haemoglobinopathy were found. The overall incidence of sickle-cell trait was 0-38%, but for the Black population it was 10%. Four Black babies and one White baby had alpha-thalassaemia. No other haemoglobinopathies were found in the White babies and no Asian baby had alpha-thalassaemia. Haemoglobin A2 was precociously developed in three babies, two of whom were coloured--probably a further example of the earlier maturity of coloured babies. The screening programme was stopped when it became cleaasily be combined with screening for metabolic disease in places where the incidence of haemoglobinopathies is higher.

Hemoglobin synthesis studies of a family with alpha-thalassemia trait and sickle cell trait

The ratio of total globin alpha to beta chain synthesis was determined in reticulocytes isolated from the blood of the members of a black family, some of whom had sickle cell trait with low blood HbS concentrations (25-30%). The results support the hypothesis that sickle cell trait individuals with low HbS concentrations also carry a gene for alpha-thalassemia.

Haemoglobin synthesis in 28 obligatory cases for alpha-thalassemia traits

In the Far East two types of alpha-thalassemia genes, namely alpha-thalassemia, (alpha-thal1), and alpha-thalassemia2 (alpha-thal2) exist. Definite diagnosis of the alpha-thal1 and alpha-thal2 traits is very difficult because their hematological findings are minimally abnormal or normal. This study attempts to characterize the heterozygotes by hemoglobin chain synthesis in reticulocytes from obligatory cases of the alpha-thal1 and alpha-thal2 traits. Twelve parents of babies with hemoglobin Bart's hydrops fetalis (obligatory alpha-thal1 trait) had the mean total radioactivity alpha/beta ratio of 0.76 +/- SD 0.04, while that of 7 normal controls was 1.06 +/- SD 0.04. The alpha/beta globin chain ratios of 16 cases, who were either parents or offspring of patients with hemoglobin H disease, were found to segregate into 2 groups, i.e. 0.78 +/- SD 0.03 (10 cases) and 0.9l1 and alpha-thal2 traits respectively. The hematological data of the first group showed definite hypochromic microcytic red cells, similar to those of the parents of the hydrops. The second group had significantly higher mean corpuscular hemoglobin than the first group, compatible with alpha-thal2 trait. Our globin chain synthesis study thus appears to be capable of discriminating normal, alpha-thal1 and alpha-thal2 traits.

Alpha thalassaemia in adults with sickle-cell trait

Mild forms of alpha thalassaemia are difficult to detect in adults. Since alpha thalassaemia existing with structural defects of the beta chain of haemoglobin may lead to decreased levels of the abnormal haemoglobin, we examined individuals having sickle-cell trait for the possible coexistence of alpha thalassaemia. Patients with sickle-cell trait having haemoglobin-S (Hb-S) levels less than commonly expected were compared to two control groups--one with sickle-cell trait and the usual levels of Hg S and one with normal haemoglobin. Twenty-one patients with sickle-cell trait having Hb-S concentrations below 35% had 65.8% Hb A, 31.8% Hb S, and a mean corpuscular volume of 81.6 fl. Studies of the relative rates of alpha-, betaS- and betaA-chain synthesis in 14 of these individuals showed a mean alpha:beta ratio of 0.76. In patients with normal haemoglobin as well as in sickle-cell trait with Hb-S levels above 35%, this ratio was unity. These findings are consistent with the presence of alpha thalassaemia in patients with sickle-cell trait who have lower than usual levels of Hb S and microcytosis.

Thalassaemia in northern Liberia. A survey in the Mount Nimba area

A population survey in northern Liberia showed an average incidence of 9 percent of beta-thalassaemia trait. There was considerable tribal variation, the highest rates being mainly found in tribes having a low incidence of Hb S. A single example of deltabeta-thalassaemia trait was also found; the incidence of delta-chain variants was 1.8 percent. The effect of malaria on Hb A2 levels was investigated but appeared to be negligible. The problems of beta-thalassaemia and Hb S occurring in the same population are discussed. It is considered that, although made on a local sample, the results of this survey indicate a high incidence of beta-thalassaemia trait elsewhere in Liberia and that this is a suitable are for investigations of linkage at beta- and delta-chain loci. No conclusion is at present possible from the data on the presence of alpha-thalassaemia although 10 percent of neonates were found to have increased levels of Hb Barts.

Beta-thalassemia in the American Negro

In Italian patients with high hemoglobin A(2) beta-thalassemia trait, the synthesis of beta-chains of adult hemoglobin in the peripheral blood is approximately one-half that of alpha-chains. In this study the relative rates of beta- and alpha-chain synthesis were determined in 26 Negro heterozygotes and five homozygotes for beta-thalassemia in six families. The beta/alpha ratio of globin synthesis was decreased in only 15 heterozygotes, whereas in the other 11, beta/alpha globin synthesis was in the normal range or was slightly increased. These unusual findings did not appear to be due to the presence of alpha-thalassemia or a hyperactive "normal" beta-allele. This study demonstrates that the beta/alpha ratio of globin synthesis in the peripheral blood is normal in some patients with beta-thalassemia trait. In five Negro homozygotes with relatively mild clinical disease the beta/alpha ratios were similar to those of Caucasians with Cooley's anemia. Further studies are needed to explore the relationship between normal synthesis ratios in many Negro heterozygotes and milder clinical disease in homozygotes in the same families.

Benign obstetric history in women with sickle-cell anaemia associated with -thalassaemia

Two Ghanaian women with sickle-cell anaemia and alpha-thalassaemia were found to have an unusually benign obstetric history. In addition to two factors present which are known to moderate the clinical course of sickle-cell anaemia, good socioeconomic status and a relatively high Hb F level, it is suggested that alpha-thalassaemia may act among other things by lowering the haemoglobin concentration in the red cells and thereby lowering their tendency to sickle in vivo.