Erythrocyte uroporphyrinogen-I-synthase activity in beta-thalassaemic patients

The haem pathway enzyme uroporphyrinogen-I-synthase (UPGS) was assayed in erythrocyte samples from twenty normal, twenty beta-thalassaemia heterozygotic and twenty beta-thalassaemia homozygotic subjects, after partial separation of the erythrocytes according to their age. UPGS erythrocyte enzyme concentration activity was significantly higher in the young than in the old erythrocytes of normal (66.5 +/- 11.8 v. 45 +/- 9.5 nmol h-1 1(-1), mean +/- SD, P less than 0.001) and beta-thalassaemia heterozygotic subjects (70.1 +/- 18.7 v. 49.8 +/- 14.5 nmol h-1 1(-1), P less than 0.001), but not in patients with homozygous beta-thalassaemia (46.0 +/- 12.8 v. 44.1 +/- 12.5 nmol h-1 1(-1), P = 0.65). Furthermore, UPGS enzyme concentration of both young and old erythrocytes of homozygous beta-thalassaemia was significantly lower than that of the young (P less than 0.001) but similar to that of the old (P greater than 0.2) erythrocytes of either normal or beta-thalassaemia heterozygotic subjects. Since severe chronic haemolysis due to haemoglobinopathies is associated with increased UPGS enzyme concentration, these results suggest that UPGS activity may be suppressed in homozygous beta-thalassaemia.