Definition: 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 tyrosinemia, 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 tyrosinemia, 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 tyrosinemia is associated with intermittent ataxia and drowsiness without liver dysfunction and is due to 4-hydroxy-phenylpyruvate dioxygenase (4HPPD) deficiency.
[tyrosine + G. haima, blood]
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