Liver Biopsy Following Gene Therapy For Hemophilia

Inclusion Criteria: * Age ≥18 to 80 years * Patients, who were enrolled and treated in one of the following clinical trials: * AGT4HB (EudraCT number: 2005-005711-17; NCT00979238) - FIX AAV gene therapy trial (sponsor: St. Jude Children's Research Hospital) * GO8 (EudraCT number:2014-003880-38; NCT02576795) - FVIII AAV gene therapy trial (sponsor: University College, London) * Able to give informed consent * Able to comply with study requirements Exclusion Criteria (Do not apply to participants who will not undergo liver biopsy, and have leftover liver tissue from a previous biopsy procedure, because all exclusion criteria only cover the safety considerations for the biopsy procedure.): * Any condition that, in the opinion of the investigator or sponsor of the ongoing clinical trial in which the patient is participating in, would prevent the patient from fully complying with the requirements of the clinical trial and/or would influence or interfere with evaluation and interpretation of subject safety or efficacy result of that ongoing clinical trial * Platelet count \<140x10\^9/L * INR \>1.5 * Abnormal kidney function with estimated GFR \<50 mL/min (calculated using the CKD-EPI equation) * Known allergy to iodine-based intravenous contrast agents * Known allergy to local or general anesthetics * Known allergic reaction to FVIII/FIX concentrate infusions * Presence of FVIII inhibitor or FIX inhibitor (historical result can be used if done within 14 weeks of this liver …