Interaction of the alpha2 polyadenylation signal mutation (AATAAA-->AATA--) and alpha0-thalassemia (--SEA), resulting in Hb H disease in a Thai patient

Curative Stem Cell Transplantation for Severe Hb H Disease Manifesting From Early Infancy: Phenotypic and Genotypic Analyses

Most people with Hb H disease live normal lives; however, a minority of cases requires lifelong regular transfusions. An atypical form of nondeletional Hb H disease was reported in a Thai boy, characterized by severe persistent hemolytic anemia since the age of 2 months. Molecular diagnosis revealed the apparent compound heterozygosity for the Southeast Asian (- -(SEA)) and α2 polyadenylation (polyA) signal (AATAAA>AATA- -) deletions. The proband was successfully treated with allogeneic hematopoietic stem cell transplantation (HSCT). Accurate phenotypic and genotypic diagnosis in atypically severe Hb H disease is helpful for the understanding of its pathophysiology, the institution of appropriate management, and provision of genetic counseling and prenatal diagnosis. Hematopoietic stem cell transplantation is a potentially curative treatment option for this severe α-thalassemia (α-thal) syndrome.

Characterization of Clinical and Laboratory Profiles of the Deletional α2-Globin Gene Polyadenylation Signal Sequence (AATAAA > AATA- -) in an Indian Population

α-Thalassemia (α-thal) is characterized by large deletions involving the variable regions of α2 and/or α1 genes. Nondeletional mutations and polyadenylation (polyA) signal sequence motif mutations are less common. In this retrospective study, we describe a fragment length analysis-based polymerase chain reaction (PCR) assay for screening the T(Indian) (AATAAA > AATA- -; HBA2: c.*93_*94delAA) polyA signal deletion along with its clinical and laboratory presentation in 21 patients. Most of the patients were diagnosed in early adulthood with a clinical presentation ranging from asymptomatic in the heterozygous state to severe Hb H disease with a prominent hemolytic component in the homozygous state. On genetic analysis, 14 patients were found to be homozygotes, five were compound heterozygotes and two were heterozygotes. Thus, the T(Indian) polyA signal deletion is common in the Indian population and should be screened for in patients with nondeletional α-thal mutations.

Nondeletional Hb Queens Park [α32(B13)Met→Lys]/Hb H (β4) disease

A rare nondeletional α-thalassemia-2 (α-thal-2) allele was identified in a Thai boy with Hb H (β4) disease. The proband has α-thal-1 (- -(SEA) type) together with a non productive Hb Queens Park (HBA1:c.98T>A) [α32(B13)Met→Lys] α1-globin variant. No abnormal hemoglobin (Hb) fraction was detected by high performance liquid chromatography (HPLC). The clinical effect of this mutation in the proband was comparable to that of deletional α-thal-2 present in Hb H disease.

A rare association of alphaO-thalassemia (--SEA) and an initiation codon mutation (ATG-->A-G) of the alpha2 gene causes Hb H disease in Thailand

Several rare and hitherto unidentified non deletional alpha-thalassemias (alphaTalpha or alphaalphaT) have been reported from Thailand within the past few years. Interactions of these determinants with alphaO-thalassemia (thal) (--/), which is highly prevalent in this region, give rise to various genotypes (--/ alphaTalpha or --/alphaalphaT) underlying Hb H disease. We report herein the interaction of a rare initiation codon mutation of the alpha2 gene and alphaO-thal in a Thai boy with Hb H disease. This finding highlights a wide variety of molecular pathology of the alpha-globin genes underlying alpha-thal syndrome in Southeast Asia.

The diverse molecular basis and hematological features of Hb H and AEBart's diseases in Northeast Thailand

We defined the molecular basis and correlated the hematological phenotypes with the globin genotypes in 52 patients with Hb H disease and 29 patients with AEBart's disease of northeast Thailand. Among the former group, the most prevalent molecular defect was found to be the interaction of alpha-thalassemia 1 (SEA type) with the Hb Constant Spring (Hb CS; 35 of 52 patients), followed by the deletion of three alpha-globin genes with the SEA type alpha-thalassemia 1 and the 3.7- or 4.2-kb deletion of alpha-thalassemia 2 (14 of 52 patients) and the interaction of the SEA alpha-thalassemia 1 with the Hb Paksé which was found in the remaining 3 patients. Among the 29 patients of the latter group, in 18 disease was caused by interactions of Hb E heterozygotes with the SEA alpha-thalassemia 1 and Hb CS. Interaction of Hb E heterozygotes with a deletional form of Hb H disease was detected in 7 patients and the Hb Paksé AEBart's disease was found in another 3 patients. A remaining patient with an unusually severe form of AEBart's disease with a lower Hb E level and observable Hb H was associated with a hitherto undescribed condition, the interaction of Hb E heterozygote with alpha-thalassemia 1 and an alpha2 codon 30 (GAG) deletion. Hematological characterization of the patients demonstrated that although disease in most of them was associated with thalassemia intermedia phenotypes, it was apparent that association with the nondeletional form of alpha-thalassemia 2 produced a more severe phenotype than that of the deletional one. Therefore, alpha-globin gene analysis of Hb H and AEBart's disease patients would be useful for predicting the clinical outcome and improving genetic counseling.

Unusual phenotypic observations associated with a rare HbH disease genotype (- -Med/alphaTSaudialpha): implications for clinical management

A single patient with a rare Haemoglobin H (HbH) disease genotype (- -Med/alphaTSaudialpha) was observed to have exceptionally high levels of HbH (> 60%) and paradoxically high total haemoglobin levels. Studies of haematological parameters, blood biochemistry and oxygen transport properties revealed a severe functional anaemia, associated with marked erythropoietic stimulation and a markedly raised cardiac output. This rare case illustrates the complexity of interactions that may be associated with the clinical course of HbH disease, highlighting that haematological parameters alone may lead to spurious evaluation of clinical status. Issues related to the therapeutic management of unusual cases are raised.