Molecular analysis of a thai beta-thalassaemia heterozygote with normal haemoglobin A2 level: implication for population screening.

BACKGROUND: This study aimed to characterize the molecular basis of a beta-thalassaemia heterozygote who had a normal haemoglobin A2 level.
METHODS: Using haematological and molecular analyses, the alpha- and beta-globin genotypes in a Thai woman with normal haemoglobin A2 level, who was identified in a thalassaemia and haemoglobinopathy screening programme, were examined.
RESULTS: The patient was positive for a 0.36% one-tube osmotic fragility test but negative for the dichlorophenolindophenol dye test for haemoglobin E. Haemoglobin A and A2 were observed on cellulose acetate electrophoresis with the haemoglobin A2 of 2.0%, compatible with an alpha-thalassaemia 1 carrier. Polymerase chain reaction analysis failed to detect alpha-thalassaemia 1 (South East Asian deletion). Beta-globin gene analysis detected a severe betao-thalassaemia allele with the 4 bp (-CTTT) deletion at codons 41/42. Further analysis of the alpha-globin gene identified the homozygosity of the 3.7 kb deletion alpha-thalassaemia 2.
CONCLUSIONS: The patient was found to be an unusual case: a betao-thalassaemia carrier with a low haemoglobin A2 concentration, in combination with a homozygosity for the 3.7 kb alpha-thalassaemia 2 deletion. The approach used to characterize the patient and the result obtained in this report will prove useful for population screening of thalassaemia in regions where both alpha- and beta-thalassaemias are common.