Detection of Hpdel among Thais, a deleted allele of the haptoglobin gene that causes congenital haptoglobin deficiency

BACKGROUND: Congenital haptoglobin deficiency is a risk factor for anaphylactic nonhemolytic transfusion reactions in Japan. The deleted allele of the haptoglobin gene, Hpdel, which causes congenital haptoglobin deficiency, has also been observed in other Northeast Asian populations, such as Korean and Chinese persons. It has not been reported in several African and European-African populations, however, or investigated in other countries. STUDY DESIGN AND METHODS: To investigate the distribution of congenital haptoglobin deficiency in Southeast Asian countries, blood samples collected from 200 randomly selected healthy Thai volunteers were analyzed for serum haptoglobin and the haptoglobin gene. Plasma haptoglobin concentration was measured to identify haptoglobin deficiency. Haptoglobin phenotyping was performed with sodium dodecyl sulfate–polyacrylamide gel electrophoresis followed by Western blotting. The presence of the Hpdel allele was determined with genomic DNA by an Hpdel-specific polymerase chain reaction (PCR) method. RESULTS: There were no haptoglobin-deficient subjects detected among the 200 Thais. Their haptoglobin phenotypes were as follows: Hp 1-1 in 10, Hp 2-1 in 81, and Hp 2-2 in 109. Six individuals heterozygous for Hpdel were detected. The frequency of the Hpdel allele was calculated to be 0.015. The prevalence of haptoglobin deficiency caused by Hpdel homozygosity was estimated to be approximately 1 in 4000. CONCLUSION: Congenital haptoglobin deficiency caused by Hpdel homozygosity is presumed to be present in Thailand as a risk factor for anaphylactic transfusion reactions with a frequency similar to that in Japan. The causative deleted allele of the haptoglobin gene, Hpdel, is distributed among Southeast Asian populations as well as among Northeast Asian populations.