Simplified Multiplex-PCR Diagnosis of Common Southeast Asian Deletional Determinants of α-Thalassemia

Abstract

α-Thalassemia double-gene deletions in cis are clinically significant because homozygosity or compound heterozygosity for such deletions leads to fetal demise or death shortly after birth. They account for the majority of cases of hydrops fetalis among couples of Southeast Asian origin. We have sequenced the −−THAI breakpoint junction in a patient and included this allele in a single-tube multiplex-PCR test for detecting common Southeast Asian α-thalassemia determinants. The assay was tested on genomic DNA samples and found to detect the −α3.7, −α4.2, −−FIL, −−SEA, and −−THAI determinants of α-thalassemia. α-Thalassemia is common throughout the tropics and subtropics and accounts for the majority of cases of hydrops fetalis among couples of Southeast Asian origin (1)(2)(3). Couples who are both carriers of a deletion that removes both the adjacent α2- and α1-globin genes on one of their chromosomes 16 (−−) are at 25% risk of having fetuses with hemoglobin (Hb) Barts hydrops fetalis syndrome. Such pregnancies are accompanied by increased risks of maternal complications [reviewed in Ref. (3)]. The −−SEA deletion is the most common double-gene deletion in cis among Southeast Asians, whereas the −−FIL and −−THAI deletions account for a smaller percentage of the double-deletion alleles (3)(4). Unlike the −−SEA deletion, the latter two deletions remove the entire α-globin gene cluster (5)(6)(7), and fetuses homozygous or compound heterozygous for the −−FIL and −−THAI deletions are thought to undergo early fetal demise and abort spontaneously. However, compound heterozygosity of −−SEA with either −−FIL or −−THAI produces Hb Barts hydrops …