What causes tyrosinemia type I?
Tyrosinemia type I is caused by a mutation in the FAH (fumarylacetoacetate hydrolase) gene on chromosome 15. Breaking down tyrosine requires several steps, and FAH is needed to break down an intermediate in the process, fumarylacetoacetate. The most common mutation results in an abnormally short FAH enzyme that is ineffective.
|
What causes tyrosinemia type II?
Tyrosinemia type II is caused by a mutation in the TAT (tyrosine aminotransferase) gene on chromosome 16. The TAT enzyme functions in the liver and is needed to convert tyrosine to the initial intermediate during its catalysis. When this gene has small substitution or deletion mutations, it can create enzymes with reduced or zero activity.
|
What causes tyrosinemia type III?
Tyrosinemia type III is caused by a mutation in the HPD (4-hydroxyphenylpyruvate dioxygenase) gene on chromosome 12. The HPD enzyme is required for the 2nd of 5 steps in tyrosine breakdown in the liver. Changes in a single amino acid or deletions impair or eliminate enzyme activity, so the substrate is instead converted to a toxic substance.
|