FAH (fumarylacetoacetate hydrolase) catalyzes the final step of tyrosine catabolism 1, converting fumarylacetoacetate to fumarate in the cytosol. The enzyme is essential for L-phenylalanine and L-tyrosine degradation 2, with deficiency causing hereditary tyrosinemia type 1 (HT1), a fatal metabolic liver disease characterized by accumulation of toxic metabolites 3. FAH loss-of-function mutations prevent normal tyrosine metabolism, leading to lethal hepatic injury if untreated 4. Beyond canonical metabolic roles, FAH undergoes oxidation at Met308 under genotoxic stress and translocates to the nucleus, where it produces fumarate that directly binds REV1 to suppress translesion DNA synthesis and enhance chemosensitivity in ovarian cancer 1. Clinically, FAH expression correlates with chemotherapy efficacy in epithelial ovarian cancer patients 1. Therapeutic strategies exploiting FAH biology include hepatocyte transplantation—both direct hiHep transplantation 2 and bioprinted hepatic organoids 56—which restore liver function in Fah-deficient mice. Additionally, engineered probiotics that enhance tyrosine degradation mitigate lethal liver injury in HT1 models 3, and CRISPR-Cas9-mediated FAH gene correction in patient-derived hepatocytes offers ex vivo gene therapy potential 7. These findings establish FAH as both a critical metabolic enzyme and an emerging therapeutic target for inherited and acquired liver diseases.