Tyrosinemia type I: A metabolic genetic disease characterized by abnormally high levels of amino acid tyrosine in blood (hypertyrosinemia) and urine (tyrosinuria) due to deficiency of an enzyme called fumarylacetoacetic hydrolase, the last enzyme in the tyrosine pathway. Tyrosinemia type I is inherited as an autosomal recessive disorder.

The disease causes cirrhosis of the liver before 6 months of age and, untreated, leads to death from liver failure. A more chronic form is characterized by progressive cirrhosis of the liver, a renal syndrome (with loss of phosphate into the urine causing rickets of renal origin and growth failure) and recurring neurologic crises. Untreated, it usually leads to death by age 10 from liver failure or hepatocarcinoma (cancer of the liver ).

A diet with a special formula that lacks the amino acids phenylalanine and tyrosine can slow the inevitable progression of the disorder. Liver transplantation provides a better long-term outcome than diet alone. A drug called NTBC that inhibits the tyrosine metabolic pathway can reverse the symptoms of tyrosinemia and help the liver and kidney tissue to return to normal.

The usual treatment of tyrosinemia today is NTBC plus diet. This permits greater than 90% survival. Infants with tyrosinemia and cancer of the liver need a liver transplant to survive.