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

Abstract

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 α0-thalassemia (--CR or --SA deletion) with α+-thalassemia (-α3.7/-α4.2/αConstant Springα). 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 α0-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.