Tyrosinemia is caused by the deficiency of ferredoxinyl acetoacetate hydrolase (FAH) in liver and kidney tissues, the gene encoding FAH is located at 15q23-q25, contains 14 exons and is about 30-50 Kb long. FAH deficiency also reduces the activity of 4-hydroxyphenylpyruvate dioxygenase (pHPPD) in the tyrosine metabolic pathway, resulting in increased blood tyrosine and urinary excretion of large amounts of p-hydroxyphenylpyruvate and its derivatives, the mechanism of which is not known. The abnormal accumulation of succinylacetone in children also has a strong inhibitory effect on the activity of δ-amino-γ-ketovaleric acid dehydrase (δ-ALAdehydrase), which affects the anabolism of porphyrins, resulting in a large urinary excretion of δ-amino-γ-ketovaleric acid (δ-ALA) and the clinical symptoms of interstitial porphyria. The activity of δ-amino-γ-ketoglutarate dehydratase in hepatocytes and erythrocytes is significantly reduced in these children, and the accumulated succinylacetone also affects cell growth, immune function, and renal tubular transport.