Molecular analysis of Hb Q-H disease and Hb Q-Hb E in a Singaporean family.

Hb Q (alpha 74Asp-His) results from a mutation in the alpha-gene such that abnormal alpha Q-chains are synthesized. The alpha Q-chains combine with the normal Beta A-chains to form abnormal Hb alpha 2Q beta 2A (Hb Q). Hb Q-H disease is rare, and has been reported only in the Chinese. We report here a Chinese family, were the mother diagnosed with Hb Q-H disease and the father with Hb E heterozygosity and a child with Hb Q-E-thalassemia. Thalassemia screening of the mother's blood revealed a Hb level of 6.8g/dl with low MCV and MCH. Her blood film was indicative of thalassemia. Cellulose acetate electrophoresis showed Hb H and Hb Q with the absence of Hb A. Globin chain biosynthesis was carried out and alpha Q- and beta-chains were detected. Normal alpha- chains were absent. Digestion of the mother's DNA with Bam HI and Bgl II followed by hybridization with the 1.5 kb alpha-Pst probe showed a two alpha-gene deletion on one chromosome and the -alpha Q chain mutant with the -alpha 4.2 defect on the other chromosome. DNA amplification studies indicated the two-gene deletion to be of the -SEA/ defect. The patient was concluded to possess Hb Q-H disease (--SEA/-alpha 4.2Q). Cellulose acetate electrophoresis of the father's blood showed the presence of Hb A, F and E. Molecular analysis of the father's DNA confirmed an intact set of alpha-genes (alpha alpha/alpha alpha). Globin chain biosynthesis of fetal blood of their child showed gamma, beta A, beta E, alpha A and alpha Q-chains. Molecular analysis of the child's DNA showed one alpha-gene deletion, thus giving a genotype of alpha alpha/-alpha 4.2Q beta beta E.