Quantitation of RNA-dependent platelet DNA polymerase in patients with myeloproliferative disorders

Platelets from 28 patients with the myeloproliferative diseases (MPD) polycythaemia vera (9), essential thrombocythaemia (6), myelofibrosis with myeloid metaplasia (5) and chronic myelogenous leukaemia (8) were examined for an RNA-dependent DNA polymerase activity using standardized conditions permitting highly reproducible quantitation. Low levels of activity were detected in platelets of normal individuals, but platelets of nearly all MPD patients (25/28) possessed higher levels. The polymerase activity correlated with diagnosis (P = 0.001) and did not correlate with platelet counts (P greater than 0.2). Quantitation of this RNA-dependent DNA polymerase activity may be a useful parameter in the diagnosis of myeloproliferative disorders.