Abnormalities of Tyrosine Metabolism

Hepatic cytosolic tyrosine aminotransferase (tyrosine transaminase) deficiency produces tyrosinemia type II, an autosomal recessive trait marked by hypertyrosine-mia and tyrosinuria. Clinical manifestations may include corneal erosions and plaques, inflammation (from intracellular crystallization of tyrosine), and mental retardation. Low-tyrosine and low-phenylalanine diets are beneficial. 

Tyrosinosis is presumably due to fumarylacetoacetate hydrolase deficiency and has a high prevalence in the French-Canadian population of Quebec. It is associated with abnormal liver function, renal tubular dysfunction, anemia, and vitamin D-resistant rickets. Transient tyrosinemia of the newborn, particularly in premature infants, is the most common form of tyrosinemia in infancy. 

Alcaptonuria is a rare metabolic hereditary disease in which homogentisic acid is eliminated in urine, which darkens upon exposure to air owing to oxidation of 

Lack of melanin production (hypomelanosis) gives rise to several hereditary disorders collectively known as albinism. Some forms result from deficiency of tyrosinase. The inheritance pattern of albinism varies with type. Affected individuals have increased susceptibility to various 

Aromatic u-amino acid decarboxylase (pyhdoxal phosphate) 

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In pernicious anemia, the bone marrow is hyperplastic and contains many large young cells which are designated megaloblasts. The peripheral blood shows severe macrocytic anemia, leucopenia with a high percentage of old polymorphonuclear leucocytes, and thrombocytopenia. Erythrocyte destruction is excessive, as manifested by an increase in the level of bilirubin in serum and a rise in urobilin excretion in the urine. An abnormality of tyrosine metabolism is demonstrated by the excretion of certain phenolic compounds in the urine. Hydrochloric acid is absent from the gastric juice. 

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