Globin synthesis in sideroblastic anaemia. I. Alpha and beta peptide chain synthesis

Transgenic rescue of erythroid 5-aminolevulinate synthase-deficient mice results in the formation of ring sideroblasts and siderocytes

Molecular defects in erythroid 5-aminolevulinate synthase (ALAS-E), the first enzyme in the heme biosynthetic pathway, cause X-linked sideroblastic anemia (XLSA). However, ring sideroblasts, the hallmark of XLSA, were not found in ALAS-E-deficient mouse embryos, indicating that simple ALAS-E-deficiency is not sufficient for ring sideroblast formation. To investigate the developmental stage-specific pathogenesis caused by heme-depletion, we attempted a complementation rescue of ALAS-E-deficiency. We exploited transgenic mouse lines expressing human ALAS-E at approximately half that of wild-type levels. In these hypomorphic embryos, most of the primitive erythroid cells were transformed into ring sideroblasts. The majority of the circulating definitive erythroid cells became siderocytes, enucleated erythrocytes containing iron deposits, and definitive ring sideroblasts were also observed. These iron-overloaded cells suffered from an alpha/beta globin chain imbalance. Despite the iron overload, transferrin receptors were highly expressed in the erythroid cells, suggesting they contribute to the formation of ring sideroblasts and siderocytes. These results indicate that a partially depleted heme supply provokes ring sideroblast formation. The experimental generation of ring sideroblasts in animals would contribute to our understanding of the iron metabolism and its disorder in erythroid cells.

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.

Positional cloning of the zebrafish sauternes gene: a model for congenital sideroblastic anaemia

Many human anaemias are caused by defects in haemoglobin synthesis. The zebrafish mutant sauternes (sau) has a microcytic, hypochromic anaemia, suggesting that haemoglobin production is perturbed. During embryogenesis, sau mutants have delayed erythroid maturation and abnormal globin gene expression. Using positional cloning techniques, we show that sau encodes the erythroid-specific isoform of delta-aminolevulinate synthase (ALAS2; also known as ALAS-E), the enzyme required for the first step in haem biosynthesis. As mutations in ALAS2 cause congenital sideroblastic anaemia (CSA) in humans, sau represents the first animal model of this disease.

Globin chain synthesis in myelodysplastic syndromes

Globin chain synthesis was studied in the reticulocytes of 30 patients with various myelodysplastic syndromes (MDS) to determine the alpha:beta globin chain synthetic ratio and its probable prognostic value. The mean (SD) value of the total alpha:beta ratio was 0.82 (0.45) ranging from 0.05 to 1.73. The same ratio in 10 normal controls was 1.01 (0.04). This difference was significant. Furthermore, the alpha:beta ratios were lower than normal in 14 patients (alpha-thalassaemia-like) (group I), almost within normal limits in 11 (group II), and higher than normal in five (beta-thalassaemia-like) (group III). In each group almost all the FAB subtypes were represented. The addition of exogenous haem in several of the test samples resulted in a slight to pronounced increase in the alpha:beta ratios, particularly in group I. In 92% of the high risk cases (refractory anaemia with excess blasts (RAEB), chronic myelomonocytic leukaemia (CMML] or 87.5% of patients who finally developed acute non-lyphoid leukaemia (ANLL) low or normal alpha:beta ratios were found. No significant correlation was noticed between alpha:beta ratios and various haematological variables or survival. It is concluded that in MDS the alpha:beta ratio varied enormously across the entire population of patients, as well as within each FAB subtype, thereby restricting its prognostic value. Although haem deficiency may be implicated in some cases of MDS, why this should be remains unclear.

Effect of isoniazid, a haem inhibitor, on globin chain synthesis in reticulocytes from non-thalassaemic and beta thalassaemic subjects

The effect of isonicotinic acid hydrazide (INH), a potent haem inhibitor, on globin chain synthesis was studied in reticulocytes from the following groups of patients: four non-thalassaemic patients (group i); five beta thalassaemia heterozygotes (group ii); three Hb S/beta thalassaemia heterozygotes (group iii); and two additional patients--one with homozygous beta thalassaemia and the other with thalassaemia intermedia (group iv). This was done to determine whether haem inhibitors depress alpha globin chain synthesis. The progressive increase of INH concentration (10-40 mmol l-1) in reticulocytes from a beta thalassaemia heterozygote resulted in a remarkable decrease of the alpha and beta chain synthesis, ranging from 80% to 97% and from 74% to 96% of control values, respectively, and in a gradual drop of alpha:beta ratio from 1.87 to 1.38. Furthermore, in the samples incubated with 40 mmol l-1 INH, a pronounced inhibition of globin chain synthesis 77 (19%) for alpha chain and 67 (27%) for beta or beta S chain) and a substantial drop of the alpha:beta or beta S ratio in samples with INH (median 1.16) compared with that in samples without INH (median 1.70) were observed. The inhibitory effect of INH was significantly or completely corrected by adding exogenous haem. It is suggested that haem inhibition and the resulting preferential diminution of alpha chain synthesis could provide a new approach to the treatment of homozygous beta thalassaemia with an excess of detrimental free alpha chain in erythroid cells.

5-Aminolaevulinic acid synthase activity in developing human erythroblasts

5-Aminolaevulinic acid (ALA) synthase activity was measured in highly purified preparations of age-matched human erythroblasts. Enzyme activity in immature normoblasts was four-fold higher than that found in late orthochromatic normoblasts. ALA synthase activity in the immature erythroblasts in primary acquired sideroblastic anaemia (PASA) was reduced and remained unchanged during further erythroid differentiation. The pattern of erythroblast ALA synthase activity in two patients with congenital dyserythropoietic anaemia (CDA) and in one patient with beta-thalassaemia intermedia was similar to that found in PASA. This study has clearly demonstrated reduced erythroblast ALA synthase activity in PASA but has also found reduced enzyme activity in conditions in which ring sideroblasts are not prominent. This would suggest that haem synthesis is abnormal in PASA but that reduced erythroblast ALA synthase activity does not inevitably lead to ring sideroblast formation.

Haem arginate as a treatment for myelodysplastic syndromes

We report on two patients with a myelodysplastic syndrome in whom the blood cell counts markedly improved during treatment with haem arginate. One patient received haem arginate only, the other haem arginate in combination with low dose androgen. The drug was given as weekly infusions of 2-3 mg/kg body weight for 8-12 weeks. In one patient the percentage of ringed and other abnormal sideroblasts in the bone marrow was clearly reduced as a result of the treatment. In both patients the effect on blood cell counts lasted for several months after the cessation of the haem arginate treatment. Eleven other patients showed no clear response. No adverse effects of the infusions were observed. Further studies on the possible therapeutic role of haem arginate are indicated.

Increased alpha:non-alpha globin chain synthesis ratios in myelodysplastic syndromes and myeloid leukaemia

Globin chain synthesis ratios (alpha:beta + gamma) in leucocyte free reticulocytes from six of 11 patients with various myelodysplastic syndromes were high, ranging from 1.28 to 2.43. High ratios were also found for reticulocytes from two of four patients with acute myeloblastic leukaemia. Of the eight cases in which high ratios were found, seven were in patients who were either undergoing leukaemic transformation or who had already transformed. The reason for these findings is not known, but an understanding of the mechanism may give us further insight into the process of leukaemic transformation.

Microcytosis in Hodgkin disease associated with unbalanced globin chain synthesis

A review of 162 patients with Hodgkin disease disclosed 36 with microcytic anemia (mean corpuscular hemoglobin values [MCV] less than 80 fl). Three patients had iron deficiency, and one had beta-thalassemia. Of the remaining 32 patients, 24 had microcytic anemia at the time of diagnosis of Hodgkin disease, and ten, including two patients with this finding initially, developed microcytic anemia in association with recurrence of Hodgkin disease. Seven patients with Hodgkin disease and normal MCV had normal alpha-to-beta-globin chain ratios (1.0 +/- 0.14). Seven patients with Hodgkin disease and MCV less than 80 fl had significantly lower alpha-to-beta chain ratios (0.66 +/- 0.05). Twelve normal controls and four with iron-deficiency anemia and MCV less than 80 fl had normal ratios. Anemia was corrected, and MCV returned to normal in all patients who responded to therapy for Hodgkin disease. In the two patients studied sequentially, abnormal alpha-to-beta-chain ratio was corrected along with the anemia.

Globin chain synthesis ratios in sideroblastic anaemia

Globin synthesis ratios were measured on reticulocytes from nine patients with primary acquired sideroblastic anaemia (SA), four patients with hereditary or congenital SA, two patients with secondary acquired SA and three patients with iron deficiency (ID). Ten of the samples from patients with SA and all the samples from patients with ID had normal ratios. Samples from three patients had significantly abnormal ratios, one from a patient with SA and acquired Hb H disease (alpha/beta 0 X 26), one from a patient with secondary acquired SA (alpha/beta 0 X 88), and one from a patient who went on to develop acute myeloblastic leukaemia (alpha/beta 1 X 36). Globin synthesis was stimulated by 100 microM haem similarly in normal, SA and ID reticulocytes. Any limitation of globin synthesis in SA and ID is therefore not easily reversible by adding haem. Inhibition of haem synthesis in nonsideroblastic reticulocytes using 4 mM isonicotinic acid hydrazide for 1 h incubation affected neither total globin synthesis nor the alpha/beta ratio. These results contradict the view that decreased haem synthesis decreases globin chain synthesis and decreases the alpha/beta globin chain synthesis ratios in human reticulocytes. Previously reported findings that haem could reverse globin chain synthesis inhibition in SA were good evidence for a primary deficiency of haem synthesis in the erythroblasts of these patients. Our inability to substantiate these findings emphasizes the need for a re-evaluation of the aetiology of sideroblastic anaemia.

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.

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.

Haem biosynthesis in refractory sideroblastic anaemia associated with the preleukaemic syndrome

The activities of 5 enzymes of the haem biosynthetic pathway and the protoporphyrin concentrations have been measured in peripheral red blood cells of 23 patients having a preleukaemic syndrome with refractory sideroblastic anaemia. A decreased delta-aminolaevulinic acid synthase (ALA-S) activity, an increased uroporphyrinogen I synthase activity and an increased red cell protoporphyrin concentration were consistent findings. Patients with abnormal leucocyte and/or platelet counts in the peripheral blood as well as patients with an excess of blast cells in the bone marrow had the lowest ALA-S activities. A further decrease in ALA-S activity was observed in 3 patients after leukaemic change in the disease. Patients having cytogenetic abnormalities showed no unique enzyme abnormalities. These results indicate that enzymatic disturbances of haem synthesis cannot be used as prognostic indicator of leukaemic transformation in refractory sideroblastic anaemia, but a very low ALA-S activity appears to accompany the development of a leukaemia in such patients.

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.

Globin chain biosynthesis in iron deficiency

Globin chain synthesis was studied in seven severely iron-deficient patients before and after treatment with iron. There was no appreciable difference between the individual pre- and post-treatment alpha/beta specific activity ratios and the mean alpha/beta ratio for each group was 1.00+/-SD 0.04. In a further six untreated iron-deficient patients the mean alpha/beta ratio was 1.00+/-SD 0.04. There was therefore no evidence that iron deficiency caused a reduction in alpha/beta ratio. Three patients with beta thalassaemia trait and coexistent iron deficiency had lower alpha/beta ratios before treatment than after treatment with iron. It appeared that iron deficiency had caused reduced alpha chain synthesis in this group. Preliminary experiments have shown that the alpha/beta specific activity ratio of purified haemoglobin A is decreased in iron deficiency, indicating an increase in the size of the free alpha chain pool. It is suggested that iron deficiency may interfere with the proteolytic mechanism normally responsible for the destruction of excess alpha chains. In combined iron deficiency and beta thalassaemia trait, the resulting increase in free alpha chains might act by negative feedback to inhibit further alpha chain synthesis (Blum et al, 1970) thereby reducing the pre-treatment alpha/beta ratio.

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.

Haem synthesis in sideroblastic anaemia

Measurement of delta-aminolaevulinic acid (ALA) synthetase has been performed in bone marrow of 24 normal subjects and 20 patients with sideroblastic anaemia (five congenital, two pyridoxine-responsive, 12 primary acquired and one secondary form due to isoniazid therapy). ALA-synthetase activity without added pyridoxal-phosphate in vitro was decreased in four of the congenital cases, and in all 12 primary acquired cases. In two of these 16 cases with low ALA-synthetase activity and in a case with sideroblastic change secondary to isoniazid therapy, the enzyme activity was corrected to normal by pyridoxal-phosphate in vitro. ALA-synthetase activity was normal in both cases of pyridoxine-responsive anaemia while they were receiving pyridoxine therapy but in one of these cases, studied at repeated intervals after withdrawal of pyridoxine therapy, the bone marrow ALA-synthetase activity fell to very low levels unless pyridoxal-phosphate was added in vitro. In this case the Km of the enzyme for pyridoxal-phosphate was substantially greater than that of a control sample. Haem synthetase activity was reduced in the bone marrow of two of six cases of primary acquired sideroblastic anaemia and in one congenital case tested but was normal in the pyridoxine-responsive patient studied on pyridoxine therapy. Nevertheless, this patient showed reduced incorporation of 14C-labelled delta-aminolaevulinic acid into bone marrow haem. It is concluded that both congenital and primary acquired sideroblastic anaemia are a heterogenous group of disorders, with different defects in haem synthesis, reduced activity of delta-aminolaevulinic acid synthetase being common but not invariable in both types. Pyridoxine-responsive (congenital) sideroblastic anaemia may be due to the presence of an abnormal ALA-synthetase apoenzyme which requires excessive amounts of the coenzyme, pyridoxal-phosphate, to achieve normal activity; other abnormalities of haem synthesis may also be present.

On the nature of sickle-cell disease in the Arabian Peninsula

The sickle-cell gene contributes substantially to the presentation of anaemia in certain areas of the Arabian Peninsula. However, the clinical presentation of the homozygous state of Hb S is less severe than that observed in other ethnic groups, such as American negroes. In the present paper, biosynthesis studies performed on reticulocytes from heterozygotes and homozygotes for the Hb S give further indications of the mild nature of sickle-cell disease in Arabia. Comparison of two affected families, from Saudi Arabia and Jordan, showed that clinical manifestation of the disease is mirrored by the biochemical and haematological findings in affected individuals. The results are discussed in terms of the effect of co-existing thalassaemia and/or iron deficiency with Hb S. It is suggested that both genetic and acquired conditions play a role in the clinical features of the disease. The mechanisms responsible for regulation of alpha-chain synthesis by iron (haem) deficiency are discussed.

Decreased ribosomal RNA content and in vitro RNA synthesis in purified bone marrow erythroblasts of patients with idiopathic ineffective erythropoiesis and DiGuglielmo disease

Ribsomal RNA content and in vitro 3H-uridine and 3H-thymidine incorporation with examined in purified marrow erythroblasts of patients with idiopathic ineffective erythropoiesis (IIE) and DiGuglielmo disease (DD) and compared with cells from normal marrows. Whereas 3H-thymidine incorporation rates were normal in all patients, 3H-uridine incorporation was 42%--75% of normal in cells from patients examined. Ribosomal RNA content was measured by spectrophotometric scanning of RNA electrophoresed on polyacrylamide gels and corrections made for contamination of the erythroblast preparations with ribosome bearing reticulocytes. In cells from every patient examined RNA content was decreased to 60--76% of normal. Uridine incorporation and rRNA content of patients with beta thalassemia minor and megaloblastic anemia were normal, suggesting that the defects observed in IIE and DD were not due to ineffective erythropoiesis per se. Since erythroblast ribosomes may be rate limiting in protein synthesis, we postulate that even a minor decrease in ribosome content might engender the ubiquitous abnormalities reported in erythroid cells in both IIE and DD.

Globin biosynthesis in sickle cell, Hb SC, and Hb C diseases

The wide range of globin synthesis ratios reported in patients with sickle cell disease casts doubt on whether the presence of genes for alpha- or beta-thalassemia in combination with Hb S can be detected by globin synthesis studies. We have studied globin synthesis in 20 patients with Hb SS who had a mean betaA/alpha ratio of 1.05+/-0.04, similar to that of 28 control children. In nine of these patients the percentage of newly synthesized radioactive alpha-chains in dimer or monomer forms was 16.3%+/-1.3, also similar to the control subjects. The remainder of alpha-chain was in hemoglobin tetramer. In nine patients with Hb SC, the (non-alpha)/alpha ratio was 0.97+/-0.04, and the free alpha-chain pool radioactivity in four patients was 14.1%+/-4.2. In three patients with Hb CC, betac/alpha ratios were 0.99, 1.07, and 1.10. These results indicate that globin synthesis ratios and alpha-chain radioactivity in the free alpha-chain pool of peripheral blood of patients with Hb SS, Hb SC, and Hb CC have narrow ranges, close to those of nonthalassemic controls. The data provide a basis for detecting syndromes with Hb S or Hb C associated with alpha- or beta-thalassemia. This precise differentiation is important for clinical studies of severity in sickle cell disease and for genetic counseling.

Variation in hemoglobin A2

The structure, properties and function of, and some biosynthetic and genetic aspects of, Hb A2 are described. The structural variants of Hb A2 are reviewed and their geographical distribution presented. Hb A2, Hb A2-Flatbush and Hb A2-Babinga are characteristic of negro populations and may have originated in Western or Central Africa. Hb A2-Sphakia is characteristic of Canadian Amerindian and Hb A2-Indonesia of Indonesian/Malay populations. Hb A2-NYU has only been found sporadically and most frequently in persons of Eastern European origin. The other three variants of Hb A2 have only been reported in a single person or in single families. Some conditions which are associated with changes in Hb A2 levels are reviewed.

Control of iron delivery to haemoglobin in erythroid cells

This paper reviews and reports the results of experiments on the mechanism by which iron is delivered from extracellular transferrin to reticulocyte mitochondria in which haem is synthesized. It is suggested that transferrin donates the iron directly to mitochondria. Transferrin seems to be bound to mitochondria during the process of iron release. When the release of iron from transferrin is blocked by haem, the iron-transferrin complex remains bound to mitochondria so that the total amount of transferrin molecules associated with mitochondria increases in haem-treated reticulocytes. This also leads to an increase in the number of transferrin molecules in the cytosol. In haem-deficient reticulocytes, the rate of dissociation of iron from transferrin is accelerated and the uptake of iron by mitochondria is increased. When the synthesis of haem is inhibited, the non-haem iron in the cytosol (i.e. mainly low-molecular-weight and ferritin iron) comes from mitochondria. Greater amounts of non-haem iron can also be induced in reticulocytes incubated with highly saturated transferrin but, in this case, iron does not seem to be accumulated in mitochondria. These results represent an experimental basis for the elucidation of the excessive non-haem iron accumulation in erythroid cells observed in various clinical conditions.

Hemoglobin Riyadh--alpha2beta2 (120(GH3)Lys replaced by Asn). A new variant found in association with alpha-thalassemia and iron deficiency

On a field trip toSaudi Arabia (M.A.F.E.H.) in which the relationship between alpha-thalassemia and iron deficiency was studied, a fast moving hemoglobin variant was noted in a 30 year old Saudi Arabian woman. Analysis of the hemoglobin variant showed that the amino acid substitution was beta120 Lys replaced by Asn. This variant had not been described previously and has been named Hb Riyadh. There was also present an alpha-thalassemia and details are given of the imbalance of globin chain synthesis. It was possible to improve considerably the balance in vitro by the addition of hemin.

Ultrastructural studies of the bone marrow in sickle cell anaemia. I. The structure of sickled erythrocytes and reticulocytes and their phagocytic destruction

Marrow aspirates from sickle cell patients were examined without prior deoxygenation and revealed the presence of a variable proportion (10-30%) of sickled red cells and reticulocytes. The main feature of sickled red cells was the presence of 17.6 nm fibres arranged in hexagonal order, and to a lesser extent in square or rectangular array, to form bundles of varying size and compactness which occupied the entire cytoplasm. The sickling pattern in reticulocytes was more variable. Some reticulocytes contained highly-ordered bundles of 17.6 nm fibres whose structure and distribution was identical to that in red cells from whiich they could be distinguished only by their content of organelles. Many reticulocytes exhibited less-organized fibre patterns ranging from localized aggregates to poorly-ordered regions of short fibres and filaments lacking apparent preferential orientation. In these cells, the bulk of the cytoplasm was not polymerized. Haemoglobin polymerization in reticulocytes led to entrapment of ribosomes in concentrated foci among the fibres. Frequently, iron-laden mitochondria were associated with sickled reticulocytes. The variation in pattern of sickling seen in reticulocytes is attributed to possible differences in concentration of Hb S. Correlative studies have shown that fibres were not induced by fixation procedures. Marked phagocytic degradation of sickled cells by macrophages was observed. The results are interpreted to indicate the possible intramedullary phagocytosis of red cells and reticulocytes, predisposed to sickling in the marrow. However, the data are also consistent with the removal of sickled elements from the circulating blood.

Homozygous haemoglobin D Punjab

A homozygote for the gene controlling Hb D Punjab is described. The diagnosis is supported by the peptide analysis of the haemoglobin and the examination of both parents. There was no anaemia or reticulocytosis and there was balanced synthesis of both the alphaA- and betaD-globin chains in reticulocytes. However, the oxygen affinity of the haemolysate had a small but significantly higher oxygen affinity than normal. The only other abnormalities were a somewhat decreased osmotic fragility and a slight anisocytosis of the red cells.

Erythraemia due to haemoglobin San Diego

A 63-year-old man with erythraemia was found to have a high affinity haemoglobin which was subsequently identified as Hb San Diego beta 109 (G11) Val leads to Met, recently described in a Filipino family (Nute et al, 1974). The oxygen affinity of the haemolysates was increased approximately two-fold at pH values between 6.04 and 7.90. The n value was nearly normal (2.5-2.9) in the upper range of saturation (70-95% oxygenation) but was somewhat diminished (1.9-2.1) below this range. In vitro biosynthesis of globin by reticulocytes showed that there was balanced synthesis of alpha and beta chains (alpha:beta ratio = 1).

Imbalance in alpha and beta globin synthesis associated with a hemoglobinopathy

In contrast to findings in the thalasemia syndromes, studies of globin synthesis in subjects with structurally abnormal hemoglobins have generally revealed equal production of alpha and beta polypeptide chains. However, in the present investigation of globin biosynthesis in vitro in blood and marrow from two subjects heterozygous for unstable hemoglobin Leiden, beta6 or 7 Glu --> O, a significant excess of alpha-chain production was revealed. A mother and daughter of northern European ancestry with mild compensated hemolytic anemia were found to have 25% hemoglobin Leiden. Increased hemolysis occurred after the ingestion of a sulfonamide and during infections. Normal levels of hemoglobin A2, 3.0 and 2.7%, and hemoglobin F, 0.8 and 0.6%, were found in the two subjects. Similar percentages of the minor hemoglobins were demonstrated in other family members without hemoglobin Leiden. After incubation of peripheral blood with [(3)H]-leucine, the beta(A)/beta(Leiden) synthesis ratio was 1.3, and the specific activity of beta(Leiden) was 1.3-2 times beta(A). These results indicate preferential destruction of the unstable hemoglobin Leiden. However, in contrast to previous studies of other unstable hemoglobins, there was excess synthesis of alpha-chains. The total beta/alpha synthesis ratio was 0.47-0.63 in peripheral blood and 0.82 in marrow. A pool of free alpha-chains was demonstrated by starch gel electrophoresis and DEAE column chromatography. The synthesis of globin chains was balanced in family members without hemoglobin Leiden. This degree of predominance of alpha-chain synthesis in subjects with hemoglobin Leiden resembles the findings in heterozygous beta-thalassemia. However, the relatively normal hemoglobin content of the cells with this abnormal hemoglobin suggests the possibility of an absolute excess alpha-chain production in the hemoglobin Leiden syndrome.

Disturbed haem and globin synthesis in reticulocytes of prenatal flexed-tailed (f-f) anaemic mice

Haem synthetase activity and co-ordination of α- and β-globin chain synthesis have been investigated in prenatal reticulocytes of congenic FL/4Re +/+Lvb/Lvband FL/1 Ref/f Lvb/Lvb, mice, which have a marked hypochromic, microcytic, siderocytic anaemia, with reduced erythrocyte numbers at birth, and also in other stocks bearing theflesion. Haem synthetase activity inf/freticulocyte homogenates was similar to that in normal cells but was markedly dependent on protoporphyrin added to the homogenate, while activity in normal cell homogenates was relatively independent of added precursor. In cultured normal prenatal reticulocytes α- and β-globin was synthesized in approximately equal amounts during a 4 h labelling period, but inf/freticulocytes there was an approximate 50% deficiency in β-globin chain synthesis. This deficiency could be repaired by added haem but not by protoporphyrin. Such a lesion is quantitatively consistent with the observed hypochromia of neonatalf/ferythrocytes. The relationship of this abnormality to effects of theflocus on early erythropoietic precursor cells is discussed.