[Genetic screening for alpha-thalassemia deletional determinants by GapPCR method]

The majority of a-thalassemia results from the large deletions in a-globin gene cluster, including both or either one of alpha-globin genes (alpha1 and alpha2). Most common a-thalassemia-2 deletions (single gene deletions) are -alpha3.7 and -alpha4.2, and alpha-thalassemia-1 deletions (double gene deletions) are --SEA, --THAI, --FIL, --MED and -(alpha)20.5 Although it is not easy to diagnose these deletions because of the high GC content at this locus and the sequence homology among psi alpha2, psi alpha1, alpha2 and alpha1 genes, these alleles can now be diagnosed by a single tube multiplex gapPCR assay. We showed here two Saudi Arabian patients with a-thalassemia trait who could be determined their gene mutations according to the method of Chong SS et al. (2000). [Case 1: 21-year-old male] GapPCR assay revealed the amplification of only -alpha3.7, whereas PCR of both a-globin genes showed no amplifications. The results indicate case 1 is a homozygote of -alpha3.7(-alpha3.7/-alpha3.7). [Case 2: 31-year-old male] GapPCR assay revealed the amplification of only -alpha3.7, and PCR of both alpha globin genes showed normal amplification. DNA sequencing of the amplified a-globin genes revealed a point mutation in the poly A site of alpha2-globin gene (AATAAA-->AATAAG), which is known as alpha(T-Saudi). Thus, case 2 was confirmed to be a compound heterozygote of -alpha3.7 and alpha(T-Saudia) alpha(-alpha3.7 / alpha(T-Saudi) alpha). This gapPCR assay is a rapid, reliable screening test for common alpha-thalassemia deletions and seems to be useful for the diagnosis of thalassemic patients without an increase of Hb A2 and/or an abnormality of beta-globin gene.