Ririe (cited in 1) reported the first case of CRVO in a patient with a history of recurrent thromboembolic events due to underlying familial antithrombin deficiency. Antithrombin, an alpha-2 glycoprotein, is a serine protease and is the major inhibitor of thrombin, factors IXa, Xa, XIa, and XIIa. Antithrombin deficiency can induce a prothrombic state (ie, a tendency to thrombosis).

The prevalence of familial antithrombin deficiency, an autosomal dominant disorder, in the general population is 1/2000 to 1/5000 and is 2% to 3% in young patients with venous thrombosis. It causes recurrent venous thrombosis especially of upper and lower extremities and visceral veins in early adulthood. Acquired decreases in antithrombin levels have been associated with cancer, severe liver disease, disseminated intravascular coagulation, and with use of oral contraceptives.