Clinical phenotypes and molecular characterization of Hb H-Paksé disease.
OBJECTIVE
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.


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.


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.
Viprakasit
Vip
V
MRC Molecular Hematology Unit, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, OX 3 9DS, UK. viprakas@molbiol.ox.ac.uk
Tanphaichitr
Voravarn S
VS
Pung-Amritt
Parichat
P
Petrarat
Siripan
S
Suwantol
Lerlugsn
L
Fisher
Chris
C
Higgs
Douglas R
DR
D000293:Adolescent; D000328:Adult; D000483:Alleles; D002648:Child; D018389:Codon, Nonsense / Q000235:genetics; D004252:DNA Mutational Analysis; D003937:Diagnosis, Differential; D005260:Female; D005838:Genotype; D005914:Globins / Q000737:chemistry / Q000235:genetics; D006447:Hemoglobin H / Q000032:analysis; D006455:Hemoglobins, Abnormal / Q000737:chemistry / Q000235:genetics*; D006801:Humans; D008297:Male; D010641:Phenotype; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D013785:Thailand / Q000453:epidemiology; D017085:alpha-Thalassemia / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics*
D018389:Codon, Nonsense; D006455:Hemoglobins, Abnormal; C099132:hemoglobin Pakse; D005914:Globins; D006447:Hemoglobin H; C035541:Hemoglobin Constant Spring