Tyrosinemia type 3 (HT3) is a rare inborn error of tyrosine metabolism caused by mutations in the HPD gene encoding 4-hydroxyphenyl-pyruvate dioxygenase, which is transmitted in an autosomal recessive trait. The disorder is characterized by tyrosine accumulation in body fluids and massive excretion of tyrosine derivatives into urine (www.orpha.net). Since it is the least frequent form of tyrosinemia, only few cases with the variable but rather mild clinical features have been described so far. We report an 11 year old girl presenting with no clinical symptoms and with normal mental development who has been diagnosed with HT3 through metabolic screening on the basis of elevated serum level of tyrosine ranging from 425 to 535 μmol/L (normal values: 29-86 μmol/L), and elevated urinary excretion of p-hydroxyphenyl derivatives confirmed genetically with the homozygous c.479A > G (p.Tyr160Cys) missense change in the HPD gene. The girl has been only presenting with recurrent proteinuria of unknown etiology. A phenylalanine- and tyrosine-restricted diet has never been administered. Presented case may suggest that high tyrosine concentration itself does not participate directly in neuronal damage described in patients with tyrosinemia type 3.
Keywords: HPD gene; Tyrosine metabolism; Tyrosinemia type III.