HPD and tyrosinemia type III: Tyrosinemia type III (OMIM 276710) is a rare inborn error of tyrosine metabolismcaused by mutations in the gene encoding the enzyme 4-hydroxyphenylpyruvatedioxygenase (HPPD), which catalyzes the conversion of 4-hydroxyphenylpyruvate tohomogentisate, the second step in the tyrosine catabolic pathway.