Tyrosinemia is a liver disease characterized by the absence of an enzyme, called FAAH (fumarylacetoacetate hydrolase), that is normally produced by the liver. This enzyme is responsible for the the metabolic transformation of tyrosine, an amino acid that is present in most animal and vegetal proteins. The disease causes an accumulation of a waste substance that damages the liver and the kidneys, thus leading to a slow degeneration of these organs.