Familial coexistence of primary antiphospholipid syndrome and factor VLeiden.

The antiphospholipid syndrome (APS) is an autoimmune thrombophilic disorder in which thromboembolism and thrombocytopenia occur. The antiphospholipid antibodies in these patients may cause acquired activated protein C resistance, whereas hereditary activated protein C resistance results from a common single point mutation in coagulation factor V (factor VLeiden). In a family of 11 members with 4 normal subjects, autoimmune thrombocytopenia was documented in 6 patients. Three out of these were found to have thrombocytopenia associated with primary APS. In addition, these 3 subjects were also heterozygous for the factor VLeiden. Only in this group of individuals did life threatening thromboembolic complications occur, while other thrombocytopenic family members showed no thrombotic manifestations. Genetic studies revealed no linkage between APS and HLA class II alleles. Taken together, we present a family with autoimmune thrombocytopenia, which is associated with primary APS in at least 50% of thrombocytopenic individuals. The coexistence of both APS and factor VLeiden in thrombocytopenic subjects, led to an increased number of thrombotic events, suggesting a critical role of combined acquired and hereditary activated protein C resistance in the development of thrombosis in this family. Since no association between APS and specific HLA groups was found, other underlying risk factors for the development of APS must be considered.