Functional Effects of the Coexistence of Hb-A with High Oxygen Affinity Hemoglobins

In carriers of abnormal haemoglobins with increased oxygen affinity, polyglobulia is the only possible functional compensation for tissue hypoxia.However, this adaptation is reduced if some Hb-A is used to synthesize hybrid haemoglobins of the type a2bAbX (heterotetramers). In fact, they display increased oxygen affinity. Four patients of this kind were studied: two carriers of Hb-Kempsey: b 99Asp-Asn, one of Hb-Gàmbara: b 82Lys-Glu, and one of Hb- Trento, a new variant with elongated b chains. Moreover, there are some cases, like that of Hb- Tak, also with elongated b chains, and Hb-Casper: b 106Leu-Pro, in which the abnormal Hb does not interact with Hb-A to form hybrids and the patient presents good functional compensation. This is demonstrated by at least three signs: the absence of polyglobulia, the good reactivity of Hb-A towards 2,3-DPG, and the absence of left- shifting of the upper half of the dissociation curve,which is commonly considered the expression of Hb-A oxygenation.