Phenotypic correction of activated protein C resistance following orthotopic liver transplantation

A 43-year-old white female underwent orthotopic liver transplantation in 1992 for cirrhosis related to primary sclerosing cholangitis. Pre-transplantation protein S (PS) studies revealed a discrepancy between PS activity and free PS antigen consistent with type II PS deficiency. Since the presence of activated protein C (APC) resistance has been reported to interfere with PS activity assays resulting in an apparent type II PS deficiency, we retrospectively tested a pre-transplantation frozen plasma sample for APC resistance. The sample was found to have an abnormal APC resistance ratio (APCR-R) of 1.71. Follow up testing 2 1/2 years post-transplantation revealed correction of the APC resistance phenotype (normalization of the APCR-R to 2.79). Analysis of DNA extracted from lymphocytes revealed the patient to be heterozygous for the FV mutation associated with APC resistance (FV Leiden). Hereditary APC resistance was confirmed by family studies which revealed the presence of APC resistance and heterozygous FV Leiden in her son. Although the patient's post-transplantation plasma FV is normal, her platelet FV remains heterozygous for FV Leiden. To what extent, if any, platelet FV Leiden in the absence of plasma FV Leiden may contribute to a predisposition to thrombosis is unknown.