High prevalence of hyperhomocyst(e)inemia in patients with juvenile venous thrombosis

We determined the prevalence of hyperhomocyst(e)inemia before and 4 hours after a methionine load (3.8 g/m2) in 80 patients (25 mean and 55 women) who had had at least one verified episode of venous thromboembolism before the age of 40 years and in 51 healthy control subjects. No patient had any of the hemostatic abnormalities known to be associated with increased risk of venous thrombosis, and all had normal renal and liver function and no evidence of neoplastic disease. Hyperhomocyst(e)inemia was defined as fasting plasma homocyst(e)ine levels or absolute postload increments of homocyst(e)ine above the normal range. According to these diagnostic criteria, 15 patients (18.8%) and 1 control subject (1.9%) had hyperhomocyst(e)inemia. In 1 of these patients only, hyperhomocyst(e)inemia could be explained by low serum concentrations of vitamin B12 and folates. The family history for venous thromboembolism was positive for 7 of the 15 patients. Family studies, performed for eight kindreds, showed that for more than half of the studied probands the abnormality was inherited. This study indicates that moderate hyperhomocyst(e)inemia is associated with an increased risk of developing venous thromboembolism at a young age and that measurements of fasting and postmethionine plasma homocyst(e)ine levels may be useful in the evaluation of patients with juvenile venous thromboembolism, particularly if their family history suggests the presence of an inherited abnormality.

The in vitro production of thromboxane B2 by platelets of diabetic patients is normal at physiological concentrations of ionized calcium

Platelets of patients with diabetes and no evidence of macroangiopathy produce normal amounts of thromboxane (Tx) B2 in vivo, whereas they usually show increased production in vitro. Since in vitro studies have been usually performed in citrated PRP, we tested the hypothesis that the discrepancy between in vivo and in vitro studies is due to the low concentration of plasma ionized calcium ([Ca2+]o) that is present in citrated PRP. In fact, low [Ca2+]o artifactually potentiates the platelet TxB2 production in vitro. Forty patients with diabetes mellitus and 37 matched controls were studied. Blood was anticoagulated with citrate, the thrombin inhibitor D-phenylalanyl-l-prolyl-l-chloromethylketone (PPACK) or both anticoagulants. Platelet aggregation, release of 14C-serotonin and TxB2 production were induced in platelet rich plasma (PRP) by several agonists. The following results were obtained: i) Citrated PRP: Arachidonic acid induced aggregation (p < 0.01) and TxB2 production (p < 0.02) were significantly greater in patients than in controls. No statistically significant differences were found with other agonists. ii) PPACK PRP: No statistically significant difference was found between diabetic platelets and controls. iii) PPACK plus citrate PRP: The results were not different from those obtained with citrate alone. Therefore, our results show that diabetic platelets produce normal amounts of TxB2 in vitro when the [Ca2+]o is physiological.