Familial deficiency of antithrombin III: evidence for heterogeneity existing within the family.

An Australian family with familial antithrombin III (AT III) deficiency is described. The deficiency inherited in an autosomal co-dominant manner is characterised by proportionate reduction in antigenically and biologically measured AT III. Some members with AT III deficiency have had major venous thromboses, and the deficiency has possibly been the cause of death in two individuals in the family. Heterogeneity was observed in laboratory and clinical findings in this family.