Different types of alpha-thalassaemia and significance of haemoglobin Bart's in neonates

Clonal hematopoiesis and acquired genetic abnormalities of the red cell: An historical review

Several syndromes affecting the red cell that mimic those induced by germline mutations may result from a somatic mutation that accompanies a myeloid malignancy. These syndromes are most notable in cases of myelodysplastic syndrome, but they are not limited to any one category of myeloid neoplasm. Their occurrence in males exceed the male predominance that is evident in myeloid neoplasms. The syndromes include disorders of globin chain synthesis (α- and β-thalassemia), heme synthesis (erythropoietic porphyria and erythropoietic uroporphyria), red cell membrane structure (elliptocytosis and spherocytosis), red cell enzyme activity (pyruvate kinase deficiency, glucose-6-phosphate dehydrogenase deficiency) and lowered expression of red cell ABO blood group antigens. This historical review describes the path to uncovering these acquired syndromes and their causal somatic mutations, where known. These syndromes often go unrecognized because of the dominant concern of the primary neoplasm. They may add to the healthcare needs of the patient.

Thalassemia review: features, dental considerations and management

Thalassemia is a genetic disorder that involves abnormal haemoglobin formation. The two main categories of thalassemia are alpha and beta thalassemia that are then divided into further subcategories. While some mild forms of thalassemia might even go unnoticed and only cause mild anaemia and iron deficiency problems in patients, other more severe forms of thalassemia can even result in death. Individuals with thalassemia can get treatment according to the level of severity of their condition. The main oral manifestations of thalassemia are Class II malocclusion, maxillary protrusion, high caries index, severe gingivitis. Any dental surgical procedure for such patients should be done under antibiotic cover and immediately after transfusion. Caution should be exercised in thalassemia patients due to complications related to compromised immunity and cardiovascular issues. Multidisciplinary approach involving dental surgeon, haematologist and orthodontist is the best advised approach.

Biochemistry testing associated with pregnancy and the newborn period -- a lot has changed since you were a baby!

Everyone has been a newborn, and everyone's mother has been pregnant. Despite the commonality of these events, medical care and the clinical chemistry laboratory's role in it have changed remarkably over the last 50 years. This review is a historical overview of clinical chemistry testing that is related to pregnancy and the newborn period.

The relationship between Hb Bart's levels in cord blood and the deletions of alpha-globin genes

A relationship between Hb Bart's levels in cord blood and the number of alpha-globin genes has been established by screening cord blood samples from 1,075 newborn babies. Diagnosis was made by gene mapping of DNA samples with restriction endonuclease digestion. The presence of Hb Bart's was determined with a discontinuous microelectrophoresis on cellulose acetate at pH 8.34. The establishment of this relationship allows an early diagnosis of alpha-thalassemia by this simple microelectrophoretic procedure.

Diagnosls of α thalassemia in the newborn. cord blood survey utilizing gene mapping

Application of the technique of gene mapping has made possible accurate assessment of the alpha thalassemia defect in cord blood samples obtained in a Sydney teaching hospital. Results showed a 5.2% incidence of the alpha+ thalassemia haplotype in the population being tested. Various hematological parameters such as hemoglobin, mean corpuscular hemoglobin, hemoglobin EPG pattern at pH 8.9 and the percentage of hemoglobin Bart's determined by elution at pH 6.7 were measured to assess which would be the most useful in diagnosis of alpha thalassemia at this time of life. The most consistent test proved to be hemoglobin EPG pattern at pH 8.9, and reasons for this are discussed.

Homozygous deletional alpha + thalassaemia associated with unequal expression of the two remaining alpha 1 genes (alpha 1A and alpha 1Q)

A Cambodian family presenting several haemoglobinopathies, Hb E, Hb Q and alpha + thalassaemia, has been investigated. DNA analysis showed that the thalassaemia syndrome corresponds to a leftward type (4.2 kb) deletional form of alpha + thalassaemia. Genotypes found in the family are: propositus -alpha A/-alpha Q, beta A/beta E., mother and older sister alpha A alpha A/-alpha Q, beta A/beta E., father alpha A alpha A/-alpha A, beta A/beta A. The propositus consistently presents an alpha Q/alpha A chain ratio of 60/40 although both chains are products of alpha 1 loci. The relatively higher expression of the alpha Q chain is not observed in the mother and therefore makes it unlikely to reflect anything other than differential expression of the maternal -alpha Q/ and paternal -alpha A/ haplotypes. This observation raises the possibility that both haplotypes are not strictly identical and that the region of the cross-over event is important for alpha gene expression.

The genetic basis of Hb Q-H disease

A Chinese family has been studied in which two siblings have haemoglobin Q-H disease. Using a combination of haematological and haemoglobin analysis, globin chain synthesis, analysis of alpha/beta globin messenger RNA ratios and restriction endonuclease mapping, it has been shown that each of these siblings has received one chromosome on which both alpha chain genes have been deleted and another on which there is only a single alpha chain locus which carries the alpha Q mutation. Their genotype is thus --/-alpha Q. Despite the fact that the haemoglobin Q mutation in this family is carried on a chromosome with a single alpha chain locus, heterozygous carriers for the variant have only 25% or less haemoglobin Q. Our observations indicate that the molecular basis for haemoglobin Q-alpha thalassaemia is similar to that for the common form of haemoglobin H disease in Orientals. Furthermore, they provide clear evidence that the level of an alpha chain variant in heterozygous carriers is not a reliable reflection of the number of alpha globin genes.

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.

Triplicated alpha-globin loci in humans

We have identified 12 individuals who are heterozygous for a chromosome with three alpha-globin genes. We determined the presence of the third alpha-globin locus by restriction endonuclease digestion and hybridization with alpha-globin cDNA probes. The three alpha-globin loci resided in an elongated fragment on digestion with EcoRI, BamHI, and Xba I, and the third locus was present in an additional 3.7-kilobase fragment on digestion with Hpa I, Sac I, and Bgl II. The locations of the restriction sites are compatible with a nonhomologous crossover mechanism producing the triple alpha loci. The frequency of the triple alpha loci was 0.0036 in American blacks and less than 0.004 in Sardinians, but was higher in Greek Crypriots (0.05). Individuals with five alpha-globin genes (alpha alpha/alpha alpha alpha) apparently showed no clinical or hematologic abnormalities.

Negro alpha-thalassaemia is caused by deletion of a single alpha-globin gene

Studies in two Jamaican Negro families, including haematological and haemoglobin analysis, haemoglobin synthesis, and globin messenger-RNA assay, have defined two alpha-thalassaemia phenotypes which resemble the severe (alpha-thalassaemia 1) and mild (alpha-thalassaemia 2) forms of the disorder described in Orientals. Genetic analysis suggests that subjects with the alpha-thalassaemia-1 phenotype are homozygous for the alpha-thalassaemia-2 determinant. Restriction-endonuclease mapping shows that alpha-thalassaemia-2 results from the deletion of one of the linked pair of alpha-chain genes. Hence the genotypes of the alpha-thalassaemia heterozygotes and homozygotes in these families are -alpha/alpha alpha and -alpha/-alpha respectively. If these are the usual alpha-thalassaemia genotypes in Negroes, these findings explain the difference in clinical expression of the disorder between Orientals and Negroes--in particular, the absence of haemoglobin Bart's hydrops and the rarity of haemoglobin-H disease in Negroes.

Acquired hemoglobin H disease in idiopathic myelofibrosis

A 68-year-old male, diagnosed 1 year previously as having myelofibrosis, developed hemolysis, red cell inclusions, and 37% Hb H. The alpha/beta globin synthetic ratio for circulating reticulocytes, determined by 3H-leucine incorporation and globin chain separation by carboxymethylcellulose chromatography in urea, was 0.049. When total RNA was purified from peripheral blood cells and translated in a wheat germ cell-free translation system, the alpha/beta ratio of the translation products was 0.26, indicating mRNA as a major cause of the globin synthetic imbalance. This study demonstrates that myelofibrosis is one setting in which acquired Hb H disease occurs; that the synthetic imbalance may be extreme; and that it can be associated with an imbalance in the activities of specific globin mRNAs.

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.

Hemoglobin Suan-Dok (alpha 2 109 (G16) Leu replaced by Arg beta 2): an unstable variant associated with alpha-thalassemia

An abnormal hemoglobin variant was detected in a seven-year old Thai girl. The clinical and hematological pictures were indistinguishable from hemoglobin H disease. Upon cellulose acetate electrophoresis at pH 8.5 an abnormal hemoglobin variant was found together with hemoglobins A and H. The variant moved slightly behind HbF and amounted to approximately 9%. Globin chain synthesis studies of peripheral blood reticulocytes incubated with tritiated leucine revealed that the total radioactivity ratio alpha-chain + variant alpha-chain/beta-chain was 0.59, while the ratio variant alpha-chain/beta-chain was 0.12. The variant hemoglobin was somewhat unstable under heat denaturation and in the isopropanol test. Structural studies by component isolation, globin chain separation, peptide mapping and aminoacid analysis of abnormal peptides showed that the leucine residue 109 of the alpha-chain was replaced by arginine. This hemoglobin mutant has not been described before and is named Hemoglobin Suan-Dok.

The isolation of structural genes from libraries of eucaryotic DNA

We present a procedure for eucaryotic structural gene isolation which involves the construction and screening of cloned libraries of genomic DNA. Large random DNA fragments are joined to phage lambda vectors by using synthetic DNA linkers. The recombinant molecules are packaged into viable phage particles in vitro and amplified to establish a permanent library. We isolated structural genes together with their associated sequences from three libraries constructed from Drosophila, silkmoth and rabbit genomic DNA. In particular, we obtained a large number of phage recombinants bearing the chorion gene sequence from the silkmoth library and several independent clones of beta-globin genes from the rabbit library. Restriction mapping and hybridization studies reveal the presence of closely linked beta-globin genes.

Mutant hemoglobins having elongated chains

Globin subunits may be elongated because of a base substitution in the termination codon, a crossover out of phase (frame shift) or a crossover in phase. This review presents structural, genetic, biosynthetic and clinical information on the eight variants having elongated chains which have been described to date.

Diagnosis of alpha-thalassemia trait from Coulter Counter 'S' indices

A number of patients of Mediterranean and Asian origins were found to have unexplained microcytic hypochromic red blood cells. Iron deficiency and beta-thalassaemia trait were both satisfactorily excluded in all of them. The haematological indices of these patients, obtained on a Coulter Model 'S' Counter, were found to be very similar to those seen in obligatory heterozygotes for alpha-thalassaemia. It is postulated that these patients were also carriers for alpha-thalassaemia. Subsequent investigation of some of these patients showed the characteristically reduced rates of alpha-chain synthesis seen in this condition. The discriminant function of England and Fraser (1973) may be of help in diagnosing this state. alpha-Thalassaemia trait should be considered in all patients of 'high-risk' ethnic origins with a blood picture suggestive of beta-thalassaemia trait but in whom the levels of Hb A2 and Hb F are within normal limits.

alpha-Thalassemia and beta-thalassemia in a Turkish family

A Turkish family is described in which three children have a clinical picture similar to that of thalassemia major, with typical red cell morphology and indices, and with about 10% Hb Bart's but without measurable amounts of Hb H. Hematological evaluation of six members of this family that included in vitro hemoglobin synthesis suggests that beta-(or delta beta-) thalassemia, beta-silent thalassemia, and mild and severe alpha-thalassemia genes are present in different combinations. The data indicate that beta/alpha chain ratios in patients with more than one type of thalassemia should be evaluated in relationship to values obtained for several relatives even though some of the thalassemia determinants may be silent in the parents.

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.

Alpha-thalassaemia trait in various racial groups in the United Kingdom: characterization of a variant of alpha-thalassaemia in Indians

Patients whose red-cell indices are suggestive of thalassaemia trait, but who have a normal haemoglobin electrophoretic pattern, may be carriers of alpha-thalassaemia. A diagnosis of alpha-thalassaemia trait was made in 44 such patients, using the incorporation of [3H]leucine by reticulocytes to measure the relative rates of synthesis of the alpha- and beta-chains of adult haemoglobin. Patients with alpha-thalassaemia trait had a reduced rate of synthesis of the alpha-chains, with a mean alpha/beta specific activity ratio of 0.79+/-SD 0.07. The mean alpha/beta specific activity ratio of 20 control subjects was 1.06+/-SD 0.08. The diagnostic value of the haemoglobin H(Hb H) preparation was assessed in proven alpha-thalassaemia heterozygotes of various races. A high proportion of 'false negative' results in Indian and Negro heterozygotes indicated that the Hb H preparations is a highly unreliable screening test for use in a multi-racial population. There was no significant difference in the mean level of Hb A2 in alpha-thalassaemia heterozygotes (2.0+/0SD 0.6) compared with that of the control group (2.1+/0SD0.5). Comparison of data from patients with alpha- and beta-thalassaemia traits showed that alpha-thalssaemia trait is the milder disorder, in terms of its effects of red-cell morphology, red-cell indices and degree of globin chain imbalance. Amongst individual patients with alpha-thalassaemia trait, there was no correlation between the alpha/beta specific activity ratio and the red-blood-cell(RBC) d the red-blood-cell (RBC) count, mean corpuscular volume (MCV) and mean corpuscular haemoglobin (MCH). This suggests that the alpha/beta ratio cannot be used to distinguish between carriers of a mild gene ('silent carriers') and carriers of a more severe disease. This is the first sutdy to characterize alpha-thalassaemia trait in Indians, in whom it appears to be a common disorder. Haematologically, alpha-thalassaemia trait in Indians is milder than that seen in Chinese and the fact that haemoglobin Bart's hydrops fetalis does not occur in Indians makes it likely that the genetics of Indian alpha-thalassaemia differ from those of the Chinese disease. A possible genetic model for Indian alpha-thalassaemia is discussed and the identification of the homozygote is seen as the first step in the determination of the underlying molecular defect.

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.

Is haemoglobin G alpha Philadelphia linked to alpha-thalassaemia?

The question, "Is Hb G alpha Philadelphia linked to alpha-thalassaemia?" was first posed because the abnormal haemoglobin is found in heterozygotes at a concentration greater than 25%, the proportion predicted from a 4 alpha-chain gene model. Globin chain biosynthesis was studied in a West Indian family in which one parent had beta + thalassaemia and the other was heterozygous for the G alpha Philadelphia chain gene. The former had a globin chain production ratio alpha/beta well above 1, while the latter had a ratio significantly less than 1. One child of the marriage had inherited the beta + thalassaemia from one parent and the G alpha Philadelphia chain gene from the other and showed the typical picture of alpha/beta-thalassaemia (alpha/beta ratio slightly above normal). It is explained in the discussion that the evidence favours a close linkage of 2 alpha-chain genes.

Haemoglobin Bart's in Saudi Arabia

The haemoglobin (Hb) patterns of 345 Shiite Saudi Arab cord bloods were examined by alkaline starch-gel electrophoresis. A fast-moving component, identified by structural analysis as Hb Bart's, was found in 52% of cases, the highest incidence of this variant yet recorded. The levels of Hb Bart's ranged from 0.5 to 16% of the total haemoglobin. The relative rates of synthesis of the alpha, beta and gamma-chains, measured by [3H]leucine incorporation, were estimated in 12 newborn Arab infants. There was an excellent correlation between the amount of Hb Bart's and the alpha/non-alpha-globin-chain production ratio. Furthermore there was a significant correlation between the level of Hb Bart's and morphological abnormalities of the red cells and the mean cell haemoglobin (MCH). These findings indicate that elevated levels of Hb Bart's in this population are due to the presence of alpha thalassaemia. The absence of hydrops fetalis and the rarity of Hb-H disease despite the intense inbreeding in this population, points to an alpha-thalassaemia genotype that is, in terms of phenotypic expression, intermediate between the heterozygous state for alpha-thalassaemia I and Hb-H disease. A possible molecular basis for this genotype is suggested.

An unusual case of hemoglobin Bart's hydrops fetalis

A baby with alpha-chain thalassemia hydrops fetalis was born to an Iraqian Jewish couple of Iraqi-Kurdish extraction. Hemoglobin Bart's constituted only 40% of the total hemoglobin, much less than usually found in alpha-thalassemia hydrops fetalis. That this is a particular expression of hemoglobin H disease is considered. The likelihood of two alpha-chain loci, rather than one alpha-chain locus, in this family, is also discussed.

Thalassaemia in Cyprus

Frequencies of the thalassaemias in Cyprus were examined by a survey of hospital inpatients and haematological investigations of adult and newborn population samples. The data indicate that 15% of the Greek and Turkish Cypriots are carriers of beta-thalassaemia genes, while 10% of the population carry alpha-thalassaemia genes. These are the highest frequencies of thalassaemia genes found today in any Caucasian population.

-thalassemia in the American Negro

In Italian and Chinese patients with the alpha-thalassemia syndromes the production of alpha-chain of normal hemoglobin is decreased relative to that of beta-chain in reticulocytes. In this study the relative rates of alpha- and beta-chain synthesis were determined in members of three Negro families with alpha-thalassemia. Two of the families had members with hemoglobin H disease and alpha-thalassemia trait, while the mother of several children with alpha-thalassemia trait in the third family was doubly heterozygous for alpha-thalassemia and an alpha-chain mutant. The alpha/beta ratios of globin synthesis in the patients with hemoglobin H disease and alpha-thalassemia trait indicated less severe biochemical defects in the peripheral blood than those previously determined in Italian and Chinese patients. In the third family, there was a heterogeneity of expression of the gene for alpha-thalassemia, including patients with normal red cell indices and synthesis ratios. These findings differ from those previously described in patients with alpha-thalassemia from other racial groups. Hydrops fetalis due to homozygous alpha-thalassemia may not occur in the Negro because of the relatively mild thalassemic defect.