Abstract: This paper presents the data of a study on ten HbQ families found in China mainland. Of the ten, 30 individuals were HbQ carriers. Three of them were double heterozygotes for HbQ and a-thalassemia genes and had HbQ-H disease, a severe hemolytic anemia associated with HbQ, H, and Q2 but no HbA or A, in their blood.
From the geographical distribution of HbQ in China, it is clear that this variant is common in the southen part of China and is consistent with the fact that HbQ is more commonly found in South-East Asia.
Analysis of chemical structure of the variant, including separation of globin chains by CMC, digestion of the abnormal a-chain with TPCK-trypsin, using finger-printing and HPLC of the tryptic digests, digestion of the abnormal peptide and HPLC of thermolytie digests, as well as analysis of amino acids composition and the sequencing of the abnormal peptide, indicated that aspartic acid was replaced by histiding at a 74.
DNA was isolated from leucocytes of the HbQ-H patients and then digested with restriction endonuclease Bgl II. The results showed that normal 12. 5 Kb a-specific fragment was absent but only one 7. 7 Kb a-specific fragment present in the Bgl II pattern, It thus indicated that these cases of HbQ-H disease corresponded to a leftward deletional form of a-thalassemia and the genotype of the patients was inentified as -aa/-.
The origin of the linkage of HbQ with leftward deletion of a-thalassemia 2 genes was diseussed and considered that it would result from: (1) HbQ mutation occurring on the a locus of the #16 chromosome bearing a deletion of gene; or (2) a chromosome crossover occurring between the two #16 chromosome bearing aghat or af, gene respectively; or (3) an unequal cross-over occurring between the two #16 chromosomes, one of which bearing a HbQ mutation on the ai locus.

Key words: Abnormal hemoglobin; Geographical distribution; Organization of a-globin genes