Compound heterozygosity for Hb Korle-Bu (beta(73); Asp-Asn) and Hb E (beta(26); Glu-Lys) with a 3.7-kb deletional alpha-thalassemia in Thai patients

Abstract

Hemoglobin (Hb) Korle-Bu (beta73; Asp-Asn) is the most frequent of the rare beta-chain variants in the population of West Africa whereas Hb E (beta26; Glu-Lys) is common among the Southeast Asian population. We report a hitherto undescribed condition in which these two beta-chain variants co-segregate. The proband was a 19-year-old Thai pregnant woman in her second trimester of pregnancy who visited our thalassemia screening unit. Cellulose acetate electrophoresis and high-performance liquid chromatography (HPLC) analysis of Hb detected one abnormal Hb in addition to the Hb E. Analysis of DNA sequences revealed a GAT-AAT mutation at codon 73 in trans to a GAG-AAG mutation at codon 26 of the beta-globin gene. Polymerase chain reaction (PCR) analysis of the alpha-globin gene cluster of the patient detected a 3.7-kb deletional alpha-thalassemia 2. Family study identified that her mother had the same genotype and her father was a simple Hb E carrier. The hematological data of these unusual cases of hemoglobinopathy are presented and compared with a simple heterozygote for Hb Korle-Bu found in another unrelated Thai family. beta-Globin gene haplotype linked to the Thai beta(Korle-Bu) and a simple DNA assay based on allele-specific PCR for rapid diagnosis of Hb Korle-Bu are also described.