tyrosinemia

tyrosinemia A genetic disorder that involves the metabolism of the amino acid tyrosine and is characterized by abnormally high levels of tyrosine in blood (hypertyrosinemia) and urine (tyrosinuria). There are several forms of tyrosinemia. Tyrosinemia type I is due to deficiency of fumarylacetoacetase, the last enzyme in the tyrosine catabolism pathway (the biochemical reactions that break down tyrosine). An acute form surfaces soon after birth, with the odor of cabbage and death from liver failure in infancy. A chronic form is characterized by chronic liver disease, rickets due to hypophosphatemia (low phosphate), and death in childhood. There is an association with liver cancer (hepatocellular carcinoma). Tyrosinemia type II is due to deficiency of the enzyme tyrosine transaminase and is characterized by the crystallization of tyrosine in painful thick areas on the palms and soles and in the cornea and often by mental retardation. Type III tyrosinemia is a rare disorder caused by a deficiency of the enzyme 4-hydroxyphenylpyruvate dioxygenase and is characterized by mild mental retardation and seizures. Tyrosinemia types I, II, and III are inherited in an autosomal recessive manner.