Molecular characterization of Hb H disease in southern Thailand

Genotypes of 260 individuals with hemoglobin H (Hb H) disease originating from various provinces in southern Thailand were characterized by multiplex PCR (M-PCR) and reverse dot blot hybridization (RDB). M-PCR was used to amplify target fragments and then hybridized with allele-specific oligonucleotide (ASO) probes which were bound on a nylon membrane. A total of eight α-thalassemia (α-thal) mutations, which produced eight Hb H disease genotypes (α⁰-thal/α⁺-thal), were detected. The most common form of α⁰-thal was -SEA with a frequency of 99.23%. The other form (0.77%) of α⁰-thal mutation was a THAI deletion (-THAI). The deletional α⁺-thal mutations comprised 3.7 kb (-α^3.7) and 4.2 kb (-α^4.2) deletions which were found in 172 (66.15%) and 5 (1.92%) alleles, respectively. The incidence of non-deletional α⁺-thal in decreasing order was Hb Constant Spring (Hb CS, α^CS) 28.85%, Hb Quong Sze (Hb QS, α^QS) 1.54%, and Hb Paksé (Hb PS, α^PS) 0.77%. The genotype characterization of Hb H disease and the development of the RDB technic for detection of α-thal mutations presented in this study enable the prenatal diagnosis of Hb Bart's hydrops fetalis syndrome.