What are the genetic changes related to tyrosinemia ?
Mutations in the FAH, TAT, and HPD genes can cause tyrosinemia types I, II, and III, respectively.  In the liver, enzymes break down tyrosine in a five step process, resulting in molecules that are either excreted by the kidneys or used to produce energy or make other substances in the body. The FAH gene provides instructions for the fumarylacetoacetate hydrolase enzyme, which is responsible for the final step of tyrosine breakdown. The enzyme produced from the TAT gene, called tyrosine aminotransferase enzyme, is involved at the first step in the process. The HPD gene provides instructions for making the 4-hydroxyphenylpyruvate dioxygenase enzyme, which is responsible for the second step.  Mutations in the FAH, TAT, or HPD gene cause a decrease in the activity of one of the enzymes in the breakdown of tyrosine. As a result, tyrosine and its byproducts accumulate to toxic levels, which can cause damage and death to cells in the liver, kidneys, nervous system, and other organs.