RESISTANCE TO ACTIVATED PROTEIN-C IN THALASSEMIC PATIENTS - AN UNDERLYING CAUSE OF THROMBOSIS

We evaluated 81 thalassaemia major and 4 thalassaemia intermedia patie nts (48 M, 37 F), median age 17 years; 62/85 patients were HCV-positiv e, 3/85 HIV-positive, 19/85 were splenectomized. Forty normal healthy children were recruited as the control group. The number of thrombotic events was studied retrospectively. Platelet poor plasma was filtered and quick-frozen at -70 degrees C until time of assay. APC resistance was measured in an activated thromboplastin time and results were exp ressed as normalized ratio. All tests were done with diluted 1 in 5 (v /v) factor V deficient plasma and with undiluted plasma. Molecular gen etic investigation of factor V gene was performed with polymerase chai n reaction, followed by digestion of amplified products with restricti on enzyme Mnl I. Data obtained with molecular investigation revealed t he presence of 4 heterozygous subjects for factor V Leiden (4.7%). Fun ctional tests were able to detect all heterozygotes for factor V Leide n both with undiluted and with diluted plasma, and there were no false negative subjects. However, undiluted plasma revealed a greater numbe r of false positive subjects (n=15) than did diluted plasma. Therefore , tests done with undiluted and diluted plasma revealed a 100% sensiti vity, while specificity was 81% for undiluted plasma and 97% for dilut ed plasma. Only one thrombotic event was observed in one of the 85 stu died patients, as a case of stroke in a thalassaemia intermedia patien t with APC resistance. In the same patient an additional thrombogenic risk factor was represented by a pronounced haematocrit increase at th e beginning of her tranfusion regimen.