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POLYCYTHAEMIA AND MICROCYTOSIS ARISING FROM THE COMBINATION OF A NEW HIGH OXYGEN AFFINITY HAEMOGLOBIN (Hb LUTON, α89 His→Leu) AND α THALASSAEMIA TRAIT

Haemoglobin variants with increased oxygen affinity commonly lead to a secondary polycythaemia which is a compensatory response to diminished oxygen delivery (Bunn & Forget, 1986). This is, however, determined by multiple factors, most notably the magnitude of the change in oxygen affinity and the circulating proportion of the high affinity haemoglobin. Alpha chain haemoglobin variants resulting from a single abnormal gene constitute only 15-2 5% of the total haemoglobin, and therefore have minimal physiological impact compared with 8 chain variants which can contribute up to half of the circulating haemoglobin. This difference in the proportions is a reflection of the different number of genes present: four a-globin and two 8-globin. The case described is an example of how the physiological effects of a functionally abnormal a chain variant can be potentiated by its interaction with a-thalassaemia, the effect of which has been to increase the circulating proportion of the abnormal haemoglobin producing a detectable erythrocytosis. The abnormality was first detected during haemoglobinopathy screening of a neonatal blood sample by isoelectric focusing (IEF), on which two abnormal haemoglobin brands were present: the major band focused between the HbS and HbF positions and the minor band between HbF and HbA. However, as the level of HbF declined and HbA increased postnatally, the relative proportions of these two bands were reversed. This indicated an a-globin abnormality, the two bands being the mutant forms of fetal (azyl) and adult (a&) haemoglobin. The parents of the newborn infant were both investigated and the father, a 3 5-year-old Pakistani man, was found to have the same variant haemoglobin on IEF. On haematological investigation the father had both a mild polycythaemia and microcytosis with the following haema-