Sequence characterization of the –THAIallele of athalassemia and rapid detection using a single-tube multiplex-PCR assay

Abstract

Alpha thalassemia is the most common inherited hemoglobinopathy in the world. It is caused most frequently by deletion of one or both cis-linked copies of the α-globin gene on chromosome 16p13.3. The most common deletions observed in Southeast Asia are the -SEA and -FIL double-gene deletions, and the -α3.7 and -α4 2 single-gene deletions. Double-gene deletions in cis are clinically significant because homozygosity or compound heterozygosity for such deletions is incompatible with post-natal life. In addition to the well-characterized -SEA and -FIL double-gene deletions, a third double-gene deletion, _THAI, has been described. Although a high incidence of the -THAI allele has been reported in Taiwan, it was recently pointed out that the Taiwanese patients in fact have the -FIL allele. We have now sequenced the breakpoint junction of the -THAI determinant of α-thalassemia. The results are consistent with previous mapping data and confirm that the -THAI allele is distinct from the -FIL allele. with the breakpoints of the former encompassing those of the latter. We have incorporated rapid PCR-based testing for this allele into a single-tube multiplex-PCR assay capable of also simultaneously detecting -FIL, -SEA, and the -α4 2 and -α3 7 single-gene deletions.