tyrosinemia type III

an extremely rare autosomal recessive disorder caused by homozygous mutation in the HPD gene (locus: 12q24-qter), which encodes 4-hydroxyphenylpyruvate dioxygenase, an enzyme important in tyrosine catabolism. It is characterized by hypertyrosinemia and massive urinary excretion of its derivatives, mild mental retardation, seizures, but absence of liver damage. Cf. hawkinsinuria.