Severe inclusion body β‐thalassaemia with haemolysis in a patient double heterozygous for β°‐thalassaemia and quadruplicated α‐globin gene arrangement of the anti‐4.2 type

Abstract

Summary.We describe a new case of an association of aglobin gene quadruplication of the anti-4.2 type with b Њ-thalassaemia. The patient, a young woman of mixed Brazilian-Portuguese origin, suffered from chronic haemolytic anaemia with splenomegaly. Bone marrow supravital staining with brilliant cresyl blue and electron microscopy studies showed large inclusion bodies in about 3% of erythroblasts. Upon immunofluorescent staining these inclusions reacted with a monoclonal antibody to a-but not to b-globin. Analysis of a-globin cluster by Southern blotting showed the presence of pathologic fragments specific for the anti-4.2 a-globin gene quadruplication. a/b mRNA ratio was higher than in cases combining a-globin triplication and bЊ-thalassaemia or in cases of bЊ-thalassaemia heterozygous state alone (18, 14·7 and 10·1 respectively). Our data confirmed the hypothesis that the clinically detectable haemolysis in this bЊ-thalassaemic patient was due to an unusually high amount of precipitated a-globin in erythroid precursors. This considerable excess of a-globin chains was due partly to the b-globin deficit caused by the presence of the bЊ-thalassaemic gene, but also to the presence of 6 active a-globin genes resulting from a-globin gene quadruplication in one chromosome.Keywords: a-globin gene quadruplication, inclusion body bthalassaemia, a/b mRNA ratio, globin mRNA quantification, thalassaemia intermedia.Rearrangements in the human a-globin cluster are amongst the most common genetic abnormalities observed in human populations. Deletions are the most common type of modification and involve the a-genes or larger areas of the cluster. However a-globin triplications are also encountered, and are a result of non-reciprocal crossing-over events (Weatherall, 1994).Association of such a-globin haplotypes (aaa/) with bЊ-thalassaemias strongly suggests that all genes are functioning, since these patients present a thalassaemia intermedia phenotype (Beris et al, 1991b;Ho et al, 1998). a-globin gene quadruplication is exceptional. To date, clinical and haematological data have been reported for six cases belonging to two families presenting this haplotype, but the information given was scanty and incomplete (Gu et al, 1987).We report a new case of a-globin gene quadruplication in association with a bЊ-thalassaemia, in a patient presenting large erythroblastic inclusions, severe ineffective erythropoiesis and haemolysis.The inclusion bodies were investigated by electron microscopy and immunofluorescence staining, using monoclonal antibodies against the a-and b-globin chains. Only the first antibody was found to react with the inclusions. Globin mRNA ratio quantification was performed, revealing, as expected, a great excess of a-globin mRNA. CASE REPORT, MATERIALS AND METHODSThe patient, a young woman of mixed Brazilian-Portuguese origin, was initially referred to our service because of chronic fatigue. Upon examination chronic haemolytic anaemia and splenomegaly were revealed with: Hb 8·4 g/dl, RBC 4·09 ×

A novel molecular basis for β thalassemia intermedia poses new questions about its pathophysiology

“…11 Analyses of ␣/␤ mRNA ratios demonstrate that the additional ␣ genes are transcriptionally active, as in a previously reported ␣␣␣␣ heterozygote with one ␤ thalassemia allele. 9 In the ␣␣␣/␣␣␣ ␤ thalassemia homozygote, the high ␣/␤ mRNA levels were also consistent with increased output from the ␣␣␣ chromosomes. The high ␣/␤ mRNA ratios are more extreme than the ␣/non␣ globin synthesis ratios in the 2 propositi, probably reflecting reduced translation of the additional ␣ globin mRNA.…”

“…Among the complex genetic interactions that underlie the intermediate forms of ␤ thalassemia there have been several reports of individuals heterozygous for ␤ thalassemia who are either homozygous for triplicated [1][2][3][4][5][6][7] or heterozygous for quadruplicated 6,[8][9][10] ␣ globin gene arrangements. However, because the frequency of these extended ␣ gene arrangements is probably low in most populations, genotypes of this kind are thought to be only rare causes of these forms of ␤ thalassemia.…”

Insight onto the Pathophysiology and Clinical Complications of Thalassemia Intermedia

“…The phenotype of TI may result from the increased production of alpha globin chains by a triplicated or quadruplicated alpha genotype associated with beta heterozygosity (8)(9)(10). Table 1 shows beta globin mutations in TI and TM that have a direct effect on modifying the amount of excess alpha chains, such as inheritance of abnormal alpha-or gamma-chain genes.…”

Molecular pathology of thalassemia intermedia

“…This case illustrates an additional mechanism leading to thalassemia intermedia: association of b-thalassemia Table 1 Silent and mild b-thalassemia mutations with a chromosome carrying more than the usual number of alpha-globin genes, very often triplicated, rarely quadruplicated a-globin-gene arrangement. 12,13 In this form of thalassemia, the severity of anemia results more from the hemolysis due to alpha chain excess than from an important deficit of Hb A production. Thalassemia intermedia resulting from this interaction (triplicated/quadruplicated a-globin gene and heterozygous severe b-thalassemia) is thus characterized by: (a) pronounced abnormalities of erythrocytes in peripheral blood smears; (b) splenomegaly; (c) microcytic anemia of varying degrees with hemolytic features; (d) Hb A2 levels comparable to those seen in b 0 -thalassemia trait; (e) high level of Hb F but less than 10% (this feature is important for differential diagnosis between thalassemia intermedia secondary to double heterozygous b 0 /b + [mild form] or b 0 , b + /bÀthalassemia silent state where Hb F is more than 10%).…”