Molecular and hematological characterization of Hb Tak and Hb Pyrgos in Thailand.

Two hemoglobin variants that migrate abnormally on gel electrophoresis were found in four unrelated Thai individuals. One variant that migrate faster than HbA but more slowly than Hb Bart's was detected in two heterozygotes. Another abnormal Hb migrating between HbA2 and HbF was found in one heterozygote and one compound heterozygote with HbE. In all cases, no microcytic anemia was observed. PCR amplification and direct DNA sequencing established that the first variant was caused by a missense mutation at codon 83 (GGC-GAC) that leads to Gly to Asp substitution previously described as the Hb Pyrgos in a Greek boy. The second variant was caused by an AC insertion at the termination codon that leads to synthesis of elongated beta-globin chain known as the Hb Tak. Beta globin gene haplotype analysis demonstrated that each variant was found on the same chromosome background in Thai individuals. The simple non-radioactive DNA assays based on allele specific polymerase chain reaction for the detection of these two Hb mutations in a routine laboratory are described.