A new form of thalassemia intermedia: Compound heterozygous beta thalassemia and hemoglobin Zurich

Abstract

To the Editor: Hemoglobin (Hb) Zurich is a type of unstable Hb disorder due to replacement of the distal histidine of the beta-chain by an arginine residue. The unstableHb inHbZurich is prone to denature and precipitate, especially after stress, resulting in hemolysis. It was first reported in 1960 in Switzerland and subsequently in the United States, Brazil, Japan, andChina.1–7 Patients with heterozygousHb Zurich are usually asymptomatic unless they are exposed to oxidant agents. The interaction of beta thalassemia with Hb Zurich has not been reported. Here, we describe a patient with compound heterozygous beta thalassemia and Hb Zurich with clinical phenotype resembling that of beta thalassemia intermedia who presented with hemolytic anemia. A 31-month-old Chinese female presented with jaundice and teacolored urine for 3 months without fever or anemic symptoms. No medication was taken prior to the onset of symptoms. Her neonatal jaundice was managed with phototherapy alone. She had unconjugated hyperbilirubinemia (total bilirubin 50 μmol/L, direct bilirubin 18μmol/L). Transaminase levelwasnormal.HepatitisB surfaceantigen was negative. She had normochromic normocytic anemia (Hb10 g/dL). Peripheral smear revealed marked anisocytosis, moderate numbers of target cells, and polychromasia (Figure 1). Reticulocyte count was elevated (5.9%). Haptoglobin level was low (<0.10 g/L). Lactate dehydrogenase level was elevated (548 U/L). Direct antiglobulin test was negative. High-performance liquid chromatography showed an elevated Hb F level (36.1%) and a variant Hb with the same retention time as Hb A2(55.1%), while Hb A was absent. Electrophoresis showed two bands: a band corresponding to Hb F and a slower migrating band located between the Hb F and Hb S positions. The Hb electrophoresis at acidic pH did not show any variant bands. No inclusion body was detected upon supravital staining. Molecular analysis by Sanger sequencing revealed a heterozygous IVS-II-654(C> T) mutation in the beta globin (HBB) gene and a heterozygous CAT(His) > CGT(Arg) substitution at codon 63 of the HBB gene resulting in Hb Zurich, thus confirming the finding of a double heterozygous beta thalassemia trait and Hb Zurich. Family screening revealed that the mother s genotype was heterozygous for the beta gene mutation IVS-II-654(C > T) (severe form of beta+ thalassemia). Her father s Hb level and red cell indices were normal. The genotypes for common alpha and 17 beta gene mutations were negative. Molecular analysis confirmed that he was an Hb Zurich heterozygote. During the subsequent 10 months, the patient had three episodes of mild hemolysis associated with intercurrent illnesses. The lowest Hb level was 9.1 g/dL. Maxillary hyperplasia and mild hepatosplenomegaly were observed. Folic acidwas given. Shewas advised to avoid sulfonamide. She did not require blood transfusion since diagnosis. The patient inherited Hb Zurich from her father, who also presented with a typical presentation with acute hemolysis after exposure to sulfonamide at a young age. There was no recurrence after avoidance of oxidant agents. Beta thalassemia trait is common in South China. The diagnosis of heterozygous Hb Zurich may be missed if the variant peak is not carefully checked for. The index case with a compound heterozygous state of beta thalassemia and Hb Zurich presented with chronic hemolytic anemia. The high Hb F in electrophoresis suggested beta thalassemia intermedia, but the father s blood tests did not reveal common beta thalassemia mutations. Only sequencing of the HBB gene disclosed the Hb Zurich mutation. Thalassemia refers to the impaired production of globulin protein subunits, whereas Hb variants refer to the production of structurally abnormal globin protein. Hb Zurich is an unstable Hb variant. Individuals with heterozygous Hb Zurich are usually asymptomatic with normal Hb levels but hemolysis upon exposure to oxidants can occur. The precipitation of heme-containing aggregates results in formation of Heinz bodies. Substitution of the distal histidine in beta globin gene leads to enlargement of space for ligand binding around the iron, which allows the entry of oxidant agents, for example, sulfonamide, causing oxidation of the heme group. Methemoglobin levels can increase up to 40%, and hemolysis can cause a 50% drop in hematocrit. Ironically, less hemolysis occurs in smokers, as the increased affinity for carbon monoxide from the opened heme pocket structure protects the Hb from oxidative denaturation.1,4,6,8–12 Homozygous state may not be viable in utero during the transition from gamma to beta chain synthesis due to significant instability when exposed to oxidants or heat and its increased oxygen affinity.4,13 The phenotype of heterozygous state of Hb Zurich and beta thalassemia resembles beta thalassemia intermedia with moderate levels of anemia and Hb F > 30%. Chronic hemolysis is indicated by persistent anemia, the presence of nucleated red blood cells, a high reticulocyte count, and persistent unconjugated hyperbilirubinemia. There are also clinical features of marrow expansion, including maxillary hyperplasia and hepatosplenomegaly. The interaction ofHbZurichwith beta thalassemia leads to a more severe phenotype than either Hb Zurich or beta thalassemia trait alone. Timely diagnosis prevents patients from potential drug-induced hemolysis and provides clues for family screening.