- A genetic metabolic disorder involving the amino acid tyrosine. The enzymatic basis of the disease is deficiency of an enzyme called fumarylacetoacetic hydrolase, the last enzyme in the tyrosine pathway. Tyrosinemia is inherited as an autosomal recessive disorder. Although generally rare, its incidence is greatly elevated in Norway, Finland, and Quebec. There are several different forms of tyrosinemia. The classic form (tyrosinemia-I) causes cirrhosis of the liver before 6 months of age and, untreated, leads to death from liver failure. A more chronic form of the disease 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 + diet. This permits greater than 90% survival. Infants with tyrosinemia and cancer of the liver need a liver transplant to survive.
* * *A group of autosomal recessively inherited disorders of tyrosine metabolism associated with elevated blood concentration of tyrosine, and enhanced urinary excretion of tyrosine and tyrosyl compounds. Type I t., due to deficiency of fumarylacetoacetase (FAH), is characterized by hepatosplenomegaly, nodular liver cirrhosis, multiple renal tubular reabsorptive defects, and vitamin D–resistant rickets; caused by mutation in the FAH gene on chromosome 15q. Type II t., due to deficiency of tyrosine aminotransferase (TAT), is characterized by corneal ulcers and keratosis of digits, palms, and soles; caused by mutation in the TAT gene on 16q. Type III t. is associated with intermittent ataxia and drowsiness without liver dysfunction and is due to 4-hydroxy-phenylpyruvate dioxygenase (4HPPD) deficiency. SYN: hypertyrosinemia. [tyrosine + G. haima, blood]
* * *ty·ro·sin·emia or Brit ty·ro·sin·ae·mia .tī-rō-si-'nē-mē-ə n a rare inherited disorder of tyrosine metabolism that is characterized by abnormally high concentrations of tyrosine in the blood and urine with associated abnormalities esp. of the liver and kidneys
* * *ty·ro·sin·e·mia (ti″ro-sĭ-neґme-ə) any of several aminoacidopathies of tyrosine metabolism characterized by hypertyrosinemia, tyrosyluria, and urinary excretion of related metabolites such as p-hydroxyphenylpyruvic acid. See also hawkinsinuria and hyperphenylalaninemia.
Medical dictionary. 2011.