Revisiting and updating molecular epidemiology of α-thalassemia mutations in Thailand using MLPA and new multiplex gap-PCR for nine α-thalassemia deletion

α-thalassemia is an inherited blood disorder that is most frequently found in Southeast Asian populations. In Thailand, molecular characterization can diagnose most patients with α-thalassemia; however, several atypical patients are also observed in routine analyses. Here, we characterized α-thalassemia mutations among 137 Hemoglobin H (Hb H) disease patients and three fetuses of Hb Bart’s hydrops, a fatal clinical phenotype of α-thalassemia. Specifically, we performed multiplex ligation-dependent probe amplification (MLPA) followed by direct DNA sequencing. We noticed common genotypes in 129 patients and eight patients had rare Hb H disease caused by compound heterozygous α(0)-thalassemia (--(CR) or --(SA) deletion) with α(+)-thalassemia (-α(3.7)/-α(4.2)/α(Constant Spring)α). Furthermore, two affected fetuses had the --(SA)/--(SEA) and one had the --(CR)/--(SEA) genotypes. Next, we developed and validated a new multiplex gap-PCR and applied this method to 844 subjects with microcytic red blood cells (RBCs) from various parts of Thailand. The frequency of heterozygous α(0)-thalassemia was dominated by --(SEA) 363/844 (43%), followed by --(THAI) 3/844 (0.4%), --(SA) 2/844 (0.2%), and --(CR) 2/844 (0.2%) mutations. These findings suggest that aforementioned four mutations should be routinely applied to increase the effectiveness of diagnosis and genetic counseling in this region.