Orphanet rare-disease nomenclature entry Orphanet_882 (Tyrosinemia type 1) (HTI) is an inborn error of tyrosine catabolism caused by defective activity of fumarylacetoacetate hydrolase (FAH) and is characterized by progressive liver disease, renal tubular dysfunction, porphyria-like crises and a dramatic improvement in prognosis following treatment with nitisinone. Also known as: FAH deficiency, Fumarylacetoacetase deficiency, Fumarylacetoacetate hydrolase deficiency, Hepatorenal tyrosinemia.