Abstract-Several studies have indicated that mild to moderate hyperhomocystinemia is a common cause of arterial occlusive disease. Whether hyperhomocystinemia per se is an independent risk factor for vein thromboembolism (VTE) is still somewhat controversial. Both genetic and nutritional factors influence plasma homocysteine levels. Therefore, we evaluated plasma total homocysteine (tHcy), folate, and vitamin B 12 levels and established, by polymerase chain reaction, the presence of the C677T mutation (A223V) in the methylenetetrahydrofolate reductase (MTHFR) gene in 220 cases with VTE without well-established prothrombotic defects. As a control group, 220 healthy subjects from the same geographic area as the cases were investigated. Hyperhomocystinemia was defined as a plasma tHcy level above the 95th percentile in the controls (18.05 mol/L). (Pϭ0.386); however, the normal MTHFR genotype (AA) appeared in control subjects only when tHcy levels were below the 80th percentile (10.57 mol/L) of the distribution, whereas in case patients, it was present at the highest tHcy levels. A strong association between mutated homozygosity (VV), low folate levels, and hyperhomocystinemia was found in both groups. We conclude that in patients with VTE who do not have coexisting prothrombotic defects, hyperhomocystinemia increases the risk of developing idiopathic and venous thrombosis; the homozygous condition for the MTHFR mutation confers a moderate risk but, together with low folate levels, it is the main determinant of mild hyperhomocystinemia in normal and thromboembolic populations.

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The biologic activity of Factor XIII was measured in four groups of patients: 20 with liver cirrhosis, ten with acute DIC, 30 with acute leukemia with DIC, and 20 with acute leukemia without DIC. In all groups, the plasma Factor XIII transamidating activity was reduced, but this deficiency was more evident in patients with DIC alone or with leukemia and DIC. The immunologic determination of the a and b subunits of Factor XIII was also performed. Both subunits were below the normal range in the groups of patients studied, except for subunit b, which was normal in patients with leukemia without coagulopathy. Acute DIC patients showed an equally reduced level of both subunits, whereas in patients with leukemia, even in the presence of a complicating coagulopathy, a lesser decrease of subunit b than subunit a was found. Both subunits were equally reduced in patients with cirrhosis, suggesting an impaired synthesis of these proteins. In conclusion, our findings do not support the use of Factor XIII subunit measurements in distinguishing between thrombin- or protease-mediated consumption coagulopathy, and they seem to suggest that the deficiency pattern of the subunits is not accounted for by a simple pathogenetic mechanism.

Two partial cDNAs for von Willebrand factor (vWF) were used to investigate gene lesions and restriction fragment length polymorphisms (RFLPs) in vW disease (vWd) and normal controls. No gene alteration was detected but two TaqI RFLPs, likely to be intronic and originating from point mutations, were found in the 3' part of vWF gene. The two TaqI RFLPs, identified by the same probe, are informative in approximately 50% of the subjects. Used in combination with two other known RFLPs, they define several haplotypes similarly distributed in vWd and normals. Linkage disequilibrium between loci identified by the RFLPs is present. In a family study the RFLP patterns demonstrate homozygosity for the affected vWF gene in a severe (type III) patient and identify several heterozygous subjects. The RFLPs analysis has been related to the haemostatic values and multimer distribution. In two of the four unrelated patients with severe vWd examined the RFLPs study indicates double heterozygosity for the affected vWF genes.