Tyrosine type I is an autosomal recessive metabolic disease in which the metabolism of tyrosine is impaired. Mutation of the fumarylacetoacetate hydrolase (FAH) gene (15q23-q25) produces too little or dysfunctional FAH. As a result, tyrosine can not be metabolized and accumulates maleylacetoacetate and fumarylacetoacetate, which are now metabolized to succinylacetoacetate and succinylacetone. These substances are hepatotoxic, nephro- and neurotoxic and also inhibit the enzyme delta-aminolevulinate dehydratase, a key enzyme in porphobilinogen synthesis.
In the early-manifested form of the disease, the first signs such as liver cell necrosis occur 15 days to 3 months after birth. There are also more recent manifestations (school-age children) which are manifested in a variety of symptoms, in particular, liver and kidney dysfunction and vitamin R-independent rickets.
Overall, there is an increased risk of liver cell carcinoma.