Resistance to activated protein c caused by factor V Leiden mutation and orthotopic liver transplantation

Background. Factor V (FV)-dependent resistance to activated protein C (APCR) is most likely caused by a point mutation in the FV gene, the so-called FV Leiden mutation (FV:Q(506)), which is a common risk factor predisposing to venous thromboembolism. Little is known about the role of FV:Q(506) in recipients of human liver grafts and the significance of acquired APCR caused by orthotopic liver transplantation (OLT). Methods. We screened blood samples of 720 patients who underwent OLT by genotyping for FV:Q(506) and by testing for APCR with two highly FV-specific tests. Apart from the existing medical records, we obtained clinical data from 551 patients on thromboembolic events (TEs) by means of a questionnaire. Results. We found 49 (6.8%) heterozygous carriers of FV:Q(506) who did not show APCR after OLT. One patient, heterozygous for FV:Q506, displayed APCR after OLT. In 35 (4.9%) noncarriers of FV:Q506 we detected APCR after OLT. In comparison with noncarriers, carriers of FV:Q(506) demonstrated more TE before transplantation (7% vs. 28%, P < 0.0005; relative risk 4.0 [95% confidence interval, 2.3-6.9]); this was also true for Budd-Chiari syndrome (1.8% vs. 10%, P < 0.005). At a median follow-up of 5 years (0, 13-12 years), we found a higher incidence of TE after transplantation in patients with "acquired" APCR (16.7% vs. 4,3%; P=0.01; relative risk 3.9 [95% confidence interval, 1.7-9.0]), which included one patient with life-threatening TE during the early postoperative phase. Conclusions. APCR caused by FV:Q506 before OLT is a risk factor for TE. OLT-related "acquired" APCR should be considered a risk factor for venous thromboembolism.