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Clinical phenotypes and molecular characterization of Hb H-Paksé disease
Vip Viprakasit1, Voravarn S Tanphaichitr, Parichat Pung-Amritt
1MRC Molecular Hematology Unit, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, OX 3 9DS, UK. viprakas@molbiol.ox.ac.uk
Insights
Hemoglobin Constant Spring (Hb CS) and Hb Paksé are common alpha thalassemias in Southeast Asia. New methods show Hb Paksé may be more prevalent than previously thought, aiding diagnosis.
Area of Science:
- Molecular Genetics
- Hematology
- Population Genetics
Background:
- Hemoglobin Constant Spring (Hb CS) is the most common non-deletional alpha thalassemia in Southeast Asia, caused by a specific gene mutation.
- This mutation is typically identified by the absence of an MseI restriction site.
- Previous diagnoses of alpha thalassemia in Thai patients were re-evaluated.
Purpose of the Study:
- To re-evaluate the molecular basis of alpha thalassemias in Thai patients with non-deletional Hb H disease.
- To investigate the prevalence of Hb Paksé and Hb CS mutations.
- To assess the diagnostic utility of a novel PCR-RFLP method.
Main Methods:
- Genomic sequencing of alpha globin genes from 30 patients with Hb H-CS disease.
- Mismatched polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis.
- Clinical and hematologic data assessment.
Main Results:
- Hemoglobin electrophoresis revealed a band resembling Hb CS in most patients.
- Five patients were diagnosed with Hb H-Paksé disease; the rest had Hb H-CS disease.
- Higher Hb H levels were observed in patients with Hb H-Paksé disease compared to Hb H-CS disease.
Conclusions:
- Termination codon mutations may have been misidentified in non-deletional Hb H disease cases.
- The Hb Paksé mutation might be underestimated and prevalent in Southeast Asia.
- Mismatched-PCR-RFLP offers a reliable diagnostic tool for population screening.
Background And Objectives:
Hemoglobin Constant Spring (Hb CS), caused by a termination codon mutation (TAA-->CAA) in the a2 gene, is the most common non-deletional type of a thalassemia in Southeast Asia. This mutation can most easily be detected by loss of an MseI-restriction site (T/TAA) spanning the termination codon. Recently, we sequenced the a globin genes from patients with a thalassemia in whom this MseI site was absent. This revealed, a previously described termination codon mutation (TAA-->TAT) associated with Hb Paksé. This prompted us to re-evaluate the molecular basis of a thalassaemia in other Thai patients with non-deletional types of Hb H disease.
Design And Methods:
DNA samples from 30 patients, previously diagnosed as having Hb H-CS disease, were characterized by direct genomic sequencing and by using a mismatched polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Clinical and hematologic data were assessed.
Results:
Hemoglobin electrophoresis in almost all 30 unrelated patients with non-deletional a thalassemia revealed a slow migrating band resembling Hb CS. Five of these patients were found to have Hb H-Paksé disease and the remainder had Hb H-CS disease. Comparing the hematology in patients with these two genotypes, no significant differences were found except that the proportion of Hb H was higher in patients with Hb H-Paksé disease.
Interpretation And Conclusions:
These results suggest that termination codon mutations may have been previously misidentified in many cases of non-deletional Hb H disease. Findings from six unrelated families described in this study suggest that the proportion of patients with the Hb Paksé mutation might be underestimated and that this mutation could be prevalent in Southeast Asia. Analysis of mismatched-PCR-RFLP, described here, was shown to provide an unequivocal diagnosis and will be applicable in population screening programs.