Elevation of Pyrimidine Enzyme Activities in the RBC of Patients with Congenital Hypoplastic Anaemia and their Parents

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Abstract
The activities of orotate phosphoribosyl transferase (OPRT) and orotidine monophosphate decarboxylase (ODC) were significantly elevated (P < 0.001) in erythrocytes (RBC) from 5 [pediatric] patients with prednisone-responsive congenital hypoplastic anemia (CHA). (OPRT: patients = 10.1-64.2 nmol/h per 109 RBC; controls = 2.8 .+-. 0.3 (mean [M] SEM, n = 37); ODC: patients = 30-124 nmol/h per 109 RBC; controls = 10.2 .+-. 0.7 (M .+-. SEM, n = 37). Of the patients, two had a less pronounced, but significant, increase of aspartate transcarbamylase activity and 3 patients had marginal increases of dihydroorotase activity. Dihydroorotate dehydrogenase activity was not detected in any CHA patient or control. In 1 patient prior to prednisone therapy, the OPRT and ODT activities were elevated 10-fold and remained elevated 3-fold after 16 mo. of therapy. An elevated enzyme pattern similar to that of RBC from CHA patients was observed in 3 parents of 3 CHA patients, but not in 3 parents of 2 other CHA patients. The activities of all 5 pyrimidine enzymes were normal for 1 patient with transient erythroblastopenia of childhood. The activities of all the pyrimidine biosynthetic enzymes were elevated in blood from patients with a young RBC population: sickle cell anemia, sickle-.beta.-thalassemia, hereditary spherocytosis, DiGuglielmo syndrome and from the newborn. Factors which affect the activities of pyrimidine enzymes in CHA may also result in diminished erythropoiesis.