Hemoglobin constant spring in bangkok: Molecular screening by selective enzymatic amplification of the α 2 ‐globin gene

Hemoglobin Constant Spring (Hb CS) is a hemoglobin variant with an elongated α‐globin chain secondary to a chain termination mutation. The diagnosis of HbCS by electrophoresis is difficult because it is present in very low amounts in the red cells of heterozygotes. Selective enzymatic amplification of the α 2 ‐globin gene and allele‐specific hybridization for Hb CS gene provided accurate diagnosis of Hb Constant Spring. We have used this approach to detect the α cs mutation in the cord blood that contained all four α‐globin genes but had Hb Bart on electrophoresis. The α cs mutation was found in six subjects whose Hb Bart levels were 3.0, 3.2, 3.7, 4.0, 4.9, and 9.8%. The latter also had −α mutation on the other chromosome, giving rise to the genotype α cs α/−α, which produced high Hb Bart. The gene frequency for α cs in the Thai calculated from a total of 406 cord blood studied in Bangkok was found to be ∼0.008.