Abstract Abstract 4213 Primary Budd-Chiari syndrome (BCS) is a rare disorder characterized by thrombosis of the hepatic outflow tract anywhere from the level of the hepatic veins to the suprahepatic inferior vena cava. Thrombophilic factors or prothrombotic disorders are found in the majority of patients. However, in around 20% of primary BCS patients still no cause can be identified, which highlights the need to further explore the etiology of this disorder. The fibrinogen γ' variant is a thrombosis risk modifier and may thus contribute to BCS. The aim of this study was to determine the role of fibrinogen γ' levels and common variations in the fibrinogen γ gene (FGG) in the etiology of BCS. Patients were recruited from the EN-Vie cohort, consisting of 163 consecutive BCS patients, enrolled in nine European countries between October 2003 and October 2005. Plasma and/or DNA was available from 118 BCS patients (50 males and 68 females; median age 37.9) and 104 healthy controls (43 males and 61 females; median age 36.8). We measured fibrinogen γ' levels by ELISA and genotyped two haplotype-tagging single nucleotide polymorphisms (SNPs): rs2066865 (10034C>T) tagged FGG H2 and rs1049636 (9340T>C) tagged FGG H3. All statistical analyses were adjusted for differences in age and sex. Fibrinogen γ' (0.50 vs 0.42 g/l; p=0.02) and total fibrinogen levels (3.0 vs. 2.8 g/l, p=0.04) were significantly elevated in BCS patients compared to controls. Also the fibrinogen γ'/total fibrinogen ratio, which adjusts for a potential acute phase induced increase of fibrinogen, was significantly elevated in BCS patients (0.17 vs. 0.15; p=0.03). Logistic regression showed a significant association between an increasing fibrinogen γ'/total fibrinogen ratio and risk of BCS (p=0.03). FGG H2 (OR 0.97; 0.96–0.98) and H3 (OR 1.02; 1.01–1.03) were significantly associated with fibrinogen γ'/total fibrinogen ratios. FGG H2 (OR 0.96; 0.64–1.46) and H3 (OR 0.86; 0.62–1.21) were not associated with BCS. In conclusion, fibrinogen γ' levels and the fibrinogen γ'/total fibrinogen ratio are significantly elevated in BCS patients. Common FGG gene variations determine the fibrinogen γ'/total fibrinogen ratio in these patients. We did not observe an association between FGG gene variations and risk of BCS. This study was carried out on behalf of the European Network for Vascular Disorders of the Liver (EN-Vie). Disclosures: No relevant conflicts of interest to declare.