Acquired hemoglobin H disease

Acquired haemoglobin H disease

Acquired haemoglobin H disease has been described in various premalignant haematological conditions and is most commonly associated with myelodysplastic and myeloproliferative syndromes. The condition is not restricted to any specific population group or geography. Affected individuals have no family or past history of alpha thalassaemia and these subjects usually suffer from severe uncompensated haemolysis. Extensive mapping and sequence analysis of the alpha globin gene cluster have demonstrated intact alpha globin genes, leading workers to conclude that an acquired in trans mechanism is responsible for the disorder. ATRX gene mutations on the X chromosome have been shown to be instrumental in the suppression of alpha globin gene expression. Despite recent advances in the understanding of its pathogenesis, the precise mechanism of acquired haemoglobin H disease remains a mystery.

Acquired alpha-thalassemia in association with myelodysplastic syndrome and other hematologic malignancies

Abnormalities of hemoglobin synthesis are usually inherited but may also arise as a secondary manifestation of another disease, most commonly hematologic neoplasia. Acquired hemoglobin disorders can be seen in any population and are not restricted to areas of the world with high incidences of inherited hemoglobinopathies. In fact, the acquired hemoglobinopathies may be more readily recognized where inherited hemoglobin abnormalities are rare and less likely to cause diagnostic confusion. Acquired alpha-thalassemia is the best characterized of the acquired red blood cell disorders in patients with hematologic malignancy, and it is almost always associated with a myelodysplastic syndrome (MDS). At least 2 molecular mechanisms for acquired alpha-thalassemia are now recognized: acquired deletion of the alpha-globin gene cluster limited to the neoplastic clone and, more commonly, inactivating somatic mutations of the trans-acting chromatin-associated factor ATRX, which cause dramatic down-regulation of alpha-globin gene expression. Here we review the clinical, hematologic, and molecular genetic features of alpha-thalassemia arising in a clonal myeloid disorder, and we discuss howATRX might affect gene expression in normal and abnormal hematopoiesis through epigenetic mechanisms.

Juvenile myelomonocytic leukemia (JMML) with the hematologic phenotype of severe beta thalassemia

A 3-year-old Filipino-American child with recurrent fever, splenomegaly, anemia, and thrombocytopenia, was found to have a hemoglobin F level of 76.9%. His reticulocyte count was elevated (4.3%), and erythroblasts were present in his peripheral blood. The child's erythrocytes were microcytic (MCV 66.9 fl) but his serum ferritin level was normal. His bone marrow at initial presentation demonstrated normal cellularity without an increase in blast cells. The disease progressed with worsening anemia, leukocytosis, and thrombocytopenia, with increased blasts in his marrow and the appearance of a mediastinal mass. His liver, spleen, and lymph nodes were found to be infiltrated with myeloblasts, supporting a diagnosis of juvenile myelomonocytic leukemia (JMML). Analysis of the child's Hb F showed a Ggamma/Agamma ratio of 2.2, which was within the characteristic range for JMML. A globin synthesis study using blood reticulocytes showed an alpha/non-alpha globin synthesis ratio of 2.24, typical of severe homozygous beta thalassemia. Southern blot analysis of blood-leukocyte DNA from the patient and his parents demonstrated no apparent abnormality in the beta-globin gene promoter or coding regions. The elevated level of Hb F in this child with JMML appeared to be part of an acquired Cooley's anemia-like hematologic phenotype.

Acquired alpha-thalassemia in preleukemia is due to decreased expression of all four alpha-globin genes

A somatic mutation(s), acquired during the evolution of preleukemia in a 75-year-old Caucasian male of North European origin, resulted in a marked decrease in alpha-globin mRNA. The small amount of alpha-globin mRNA present in bone marrow cells was normally processed, had a normal (alpha 1/alpha 2)-globin mRNA ratio, and was translated normally. No detectable zeta-globin mRNA was found. The alpha- and zeta-globin genes were both hypomethylated and restriction endonuclease maps of the alpha- and zeta-globin genes were comparable in the patient's marrow and fibroblast DNA. The data are most consistent with the acquisition of a mutation(s) that resulted in decreased expression of all four alpha-globin genes.

Clinical features and molecular analysis of acquired hemoglobin H disease

The presence of hemoglobin H (beta 4), resulting from a deficiency of alpha-globin chain synthesis, was observed as an acquired characteristic in the red cells of five elderly patients with myeloproliferative disorders or preleukemia. The variability in amount of hemoglobin H and in the alpha/beta globin synthesis ratios in these patients is most likely explained by the relative proportions of normal and abnormal cell populations in the peripheral blood, since some reticulocyte fractions with balanced alpha/beta globin synthesis ratios and others with almost no detectable alpha-chain production could be obtained from these patients. In one patient, the hemoglobin H virtually disappeared despite continuing disease. The amount of cytoplasmic alpha-mRNA matched the proportion of alpha-chain synthesis and, in one patient, this was also true for nuclear RNA. However, extensive analysis of the alpha-globin gene complex by restriction endonuclease mapping revealed no detectable rearrangements of the normal gene organization in any of these patients, suggesting that transcription of each pair of alpha-globin genes on each chromosome 16 is defective. These observations have important implications for both the normal regulation of alpha-globin gene expression and the molecular basis of the underlying defect that is associated with the neoplastic transformation of these cells.

Bone marrow and peripheral blood globin chain biosynthesis in iron deficiency

Globin chain synthesis was studied in 13 iron-deficient patients. The mean whole-cell globin alpha/beta ratio in the peripheral blood of 11 patients was 1.05 +/- 0.06 which is similar to the value 0.99 +/- 0.08 obtained for 10 controls. The ratios obtained for stroma-free globin were not significantly different from those of whole cell preparations. In contrast, the alpha/beta ratio of bone marrow was 0.73 +/- 0.14 in 10 iron deficient patients, which is significantly lower than that of controls. Two other patients had decreased alpha/beta ratios in the peripheral blood, probably because of the presence of an alpha-thalassemia gene. These results demonstrate a reduced rate of synthesis of alpha chains relative to that of beta chains in the bone marrow of iron-deficient patients that is not demonstrable in the peripheral blood.

Hemoglobin biosynthesis in juvenile erythroleukemia: evidence of imbalanced globin chain synthesis

In three young patients with erythroleukemia in whom a partial reversion to the fetal pattern of erythropoiesis occurred there was found additionally an imbalance of globin chain synthesis. The synthesis of beta- plus gamma-chains exceeded that of the alpha-chains. In contrast, physiologic hemoglobin F production occurring in newborn infants and increased hemoglobin F production due to rapidly regenerating erythropoiesis in hereditary spherocytosis and after acute erythroblastopenia are characterized by a well balanced globin chain synthesis. These studies indicate that in distinct cases of juvenile erythroleukemia the genuine reversion to fetal erythropoiesis may be associated not only with a depression of hemoglobin synthesis but also with an imbalanced globin chain synthesis. Unlike adult cases of erythroleukemia without reversion to fetal erythropoiesis the imbalance of globin chain synthesis seems to be a more generalized phenomenon in these cases of juvenile erythroleukemia which is not confined to a particular red cell population.

Balanced globin synthesis in idiopathic myelofibrosis

Four patients with idiopathic myelofibrosis were found to have microcytic and/or hypochromic red cell indexes. The alpha/beta globin synthetic ratio determined by incubating peripheral blood with [14C]leucine was within normal limits in all patients studied. This is unlike a recent report of acquired hemoglobin H disease with decreased alpha/beta synthetic ratio in primary myelofibrosis. This indicates that mechanisms other than alpha-thalassemia-like defects may also be involved in the production of microcytic and hypochromic red cells in myelofibrosis.

Myeloproliferative syndrome with sideroblastic anemia and acquired hemoglobin H disease

Hemoglobin H disease usually occurs as a result of inheritance of the genes for alpha thalassemia; however, occasionally patients acquire hemoglobin H in association with hematologic malignancy. This report concerns a 63-year-old Filipino man with a myeloproliferative syndrome with marked thrombocytosis and apparently acquired hemoglobulin H disease. The patient had hemolytic anemia, dimorphic red blood cells (RBC) and abundant ringed sideroblasts in the marrow. The peripheral blood contained 27% hemoglobin H and about two-thirds of his RBC had hemoglobin H inclusion bodies. There was no previous history of anemia or evidence of thalassemia in two siblings or nine adult children of the patient. In vitro studies of globin chain synthesis documented markedly decreased production of alpha globin with alpha/beta biosynthetic ratios of 0.05 in peripheral blood reticulocytes and 0.10 in bone marrow cells. The relative concentration of mRNA for alpha globin was approximately 20-fold less than that of beta globin, apparently accounting for the deficiency in alpha globin synthesis.

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.

Acquired haemoglobin H disease, complicating a myeloproliferative syndrome: a case report

A case of acquired haemoglobin H disease in association with a myeloproliferative disorder is described. Severe haemolysis with hypochromic microcytic anaemia was present. Haemoglobin H formed 18% of the circulating haemoglobin and 60% of the red cells showed multiple inclusions on incubation with brilliant cresyl blue. Blood film and absolute red cell values from a previous unrelated illness were normal, proving the acquired nature of the haemoglobin abnormality. Alpha/beta chain synthesis was measured in vitro and the degree of imbalance (alpha/beta ratio 0.39) was similar to that seen in the inborn thalassaemic disorder. A small proportion of red cells showed i-antigen reactivity but their haemoglobin H content was no different from the majority of cells which were l-antigen positive.

Variations in globin synthesis in delta-beta-thalassaemia

Peripheral blood globin synthesis studies were done in 11 patients with delta beta-thalassaemia trait, Hb S-delta beta-thalassaemia or delta beta/betao-thalassaemia from two black and two Caucasian families. All patients had elevated Hb F and normal or decreased Hb A2 levels and 10 had family studies confirming the diagnosis. In addition, four unrelated non-thalassaemic patients with elevated Hb F levels also had peripheral blood globin synthesis studies. The beta/alpha specific activity globin synthesis ratios in the three blacks with delta beta-thalassaemia trait were 0.60--1.04. In the four Caucasians with delta beta-thalassaemia traint, the beta/alpha ratios were 0.58--1.02. These results demonstrate a wide range of ratios overlapping those of normal controls (0.99 +/- 0.06). The betas/alpha ratios in three blacks with Hb S-delta beta-thalassaemia ranged from 0.66 to 1.00, similar to those of patients with delta beta-thalassaemia trait. In the black patient with delta beta/betao-thalassaemia, the gamma/alpha ratio was 0.67. The beta/alpha peripheral blood ratios in the four non-thalassaemia patients with elevated Hb F ranged from 1.00 to 1.11, similar to those of normal controls. These studies indicate that a decreased beta/alpha ratio is not an invariable finding in delta beta-thalassaemia in blacks or Caucasian patients and that globin synthesis data alone is insufficient to diagnose definitively heterozygotes for delta beta-thalassaemia or to distinguish this trait from non-thalassaemic haematological disorders associated with a normal percentage of Hb A2 and an elevated level of Hb F.

Erythroid cell differentiation

We have reviewed erythroid cell differentiation from two points of view: 1) differences between fetal and adult human red cells with particular reference to alterations which can occur in the normal pattern of erythroid cell development during the course of leukemia; 2) beochemical events which occur during erythroid cell maturation, as a model system for the study of the control of gene expression. During the course of many leukemias there is the synthesis of red cells containing fetal hemoglobin. In most cases this phenomenon is limited to a small population or clone of red cells and probably represents a nonspecific response of the bone marrow to a hematologic stress. However, in juvenile chronic myeloid leukemia and, in rare cases of erythroleukemia, there is a major reversion to fetal erythropoiesis, with progressive increase in fetal hemoglobin levels and synthesis of red cells which contain not only fetal hemoglobin but have a true fetal pattern of protein synthesis affecting proteins other than Hb F, namely Hb A2, carbonic anhydrase and the membrane antigens i and I. In this case, the fetal erythropoiesis may be a more specific manifestation of the leukemic process and may be related to the phenomenon of fetal protein synthesis (alpha-fetoprotein of carcinoembryonic antigen) observed in other types of neoplasia. Further information on the etiology and pathogenesis of abnormal cell proliferation and differentiation in the leukemias can be obtained by the study of experimental systems permitting the investigation of the regulation of gene expression in differentiating mammalian cells. Maturing erythroid cells provide a promising system for such investigations for many reasons: differentiating erythroid cells can be obtained relatively free of other cell types; a large amount of a well characterized product, hemoglobin, is synthesized; techniques are now available that permit isolation of erythroid precursors at different stages of differentiation (5-8); and finally, highly sensitive methods of measuring globin mRNA levels by DNA-RNA hybridization are currently available (13, 26, 27). We have used such techniques to measure levels of globin mRNA in separated populations of murine erythroid cells at different stages of maturation. These studies demonstrated a correlation between globin mRNA content and degree of morphological maturation. In the least well differentiated cells, however, there appeared to be a disproportionate amount of mRNA for the level of hemoglobin synthesis in these cells. These results suggest the presence of some translational control of globin mRNA in the early stages of erythroid development, although the major control of globin gene expression in this system seems to be at the transcriptional level...

Abnormal hemoglobin synthesis in some leukemic patients

Hemoglobin chain synthesis during leukemic processes has been studied on patients having fetal hemoglobin. All cases showed the following abnormalities : (1) a relatively increased synthesis of the beta chain ; (2) an important increase of the free dimeric precursors pool, with, most of the time, a predominance of alpha chain. If the first point suggests an alpha-thalassemia feature, the presence of free alpha chains shows evidence for a more complex mechanism not only due to a decrease of messenger RNA. The hypothesis of a clonal disorder could neither be demonstrated nor ruled out. The observed abnormalities could be due to a defect in a alpha chain depending regulation mechanism.

Regulation of hemoglobin beta-chain synthesis in bone marrow erythroid cells by alpha chains

Synthesis of alpha and beta chains of hemoglobin was studied in vitro in intact reticulocytes and bone marrow cells. The cells were from rabbits having a variant form of hemoglobin in which L-isoleucine is in the alpha but not in the beta chains. This characteristic permitted a selective inhibition of alpha-chain synthesis to be produced by addition to the incubation medium of L-O-methylthreonine, an inhibitor of protein synthesis that is a specific antagonist of L-isoleucine. In studies with reticulocytes, 25 mM L-O-methylthreonine produced a 60-70% inhibition of alpha-chain synthesis, but beta-chain synthesis was unaffected even after incubation times for 4 hr. Because reticulocytes contain a pool of uncombined alpha chains which might have obscured the demonstration of an alpha chain-dependent mechanism for beta-chain synthesis, subsequent studies were done with bone marrow cells. The latter had little or no detectable alpha-chain pool. A substantial inhibition of alpha-chain synthesis by the bone marrow cells was produced by the isoleucine antagonist but was also accompanied by a significantly decreased rate of beta-chain synthesis. These findings suggest that the coordinated synthesis of the complementary alpha- and beta-globin chains of hemoglobin may reflect in part a modifying effect of alpha-chain synthesis on the synthesis of beta chains.