UNSTABLE ALPHA-CHAIN HEMOGLOBIN-VARIANTS WITH FACTITIOUS BETA-THALASSEMIA BIOSYNTHETIC RATIO - HB QUESTEMBERT (ALPHA-131[H14] SER-]PRO) AND HB CAEN (ALPHA-132[H15] VAL-]GLY)

Hb Questembert [alpha131(H14) Ser-->Pro] was found in several members of a French family suffering from congenital Heinz body anemia. The unstable hemoglobin was expressed in the peripheral red blood cells at a very low level. Globin biosynthetic studies revealed a high specific activity of the abnormal chain and an alpha-/beta-labeling ratio similar to that of beta-thalassemia trait. Hb Caen [alpha132(H15) Val-->Gly] is another unstable variant with the same globin biosynthesis abnormality. In both cases the structural modification is localized at the end of the H helix, a region encoded by the third exon. The mechanism for the unbalanced globin synthesis is not yet clear. It may be related 1) to a defect in chain assembly, 2) to an increased rate of degradation of the variant chain followed by the release of unlabeled beta-chains from the abnormal hemoglobin, thus leading to an apparent suppression of beta-chain synthesis, or 3) to a modified stability of the abnormal alpha-globin mRNA.