Tyrosinemia is an autosomal recessive clinical syndrome with abnormal tyrosine metabolism, severe liver injury and renal tubular defects due to fumaryl acetoacetate hydrolase deficiency. Etiology: There are two main causes of tyrosinemia in general, namely deficiency of certain enzymes and impaired absorption of amino acids. The former is a known deficiency or reduction in the activity of an enzyme or an enzyme that is not yet certain, such as phenylalanine hydroxylase deficiency causing phenylketonuria; maple syrup urine disease caused by a deficiency or reduction in the branching amino acid alpha-keto acid decarboxylase; isovaleric acidemia caused by isovaleric coenzyme A dehydrogenase deficiency; homocystinuria caused by cystathionine synthase deficiency; argininemia caused by arginase deficiency; lysine ketone The deficiency of glutarate reductase causes hyperlysinemia, etc. Amino acid absorption disorders are caused by amino acid reversion and absorption disorders, often in the intestine or other tissues, such as liver-brain-renal syndrome and Hartnup disease. Inherited tyrosinemia is autosomal recessive and is caused by a defect in the gene encoding johnsonyl acetoacetate hydrolase on chromosome 15, resulting in tyrosinemia and metabolite accumulation. Hartnup disease is caused by a defect in the neutral amino acid transporter protein, the causative gene for which is located on chromosome 2, and is passed on to offspring by females carrying the causative gene. Due to impaired transport of tryptophan through the renal tubules, there is increased excretion of these amino acids in the urine and feces, with large amounts of urinary blue mother excretion, mainly indolol sulfate, especially after eating foods containing large amounts of L-tryptophan, and also large amounts of abnormal non-hydroxylated indole metabolites in the urine. Loss of tryptophan due to large amounts excreted in the urine reduces the synthesis of nicotinic acid as a raw material for synthesis, leading to tyrosinemia.