Disorders of tyrosine metabolism

Abstract

Six inherited disorders of tyrosine metabolism are known. Hereditary tyrosinaemia type I is characterised by progressive liver disease and renal tubular dysfunction with rickets. Hereditary tyrosinaemia type II (Richner-Hanhart syndrome) presents with keratitis and blistering lesions of the palms and soles and neurological complications. Tyrosinaemia type III may be asymptomatic or associated with mental retardation. Hawkinsinuria may be asymptomatic or present with failure to thrive and metabolic acidosis in infancy. In alkaptonuria, symptoms of osteoarthritis usually appear in adulthood. Maleylacetoacetate isomerase deficiency is associated with asymptomatic mild hypersuccinylacetonaemia. Other inborn errors of tyrosine metabolism include oculocutaneous albinism caused by a deficiency of melanocyte-specific tyrosinase, converting tyrosine into DOPA-quinone; deficiency of tyrosine hydroxylase, the first enzyme in the synthesis of dopamine from tyrosine; and deficiency of aromatic L-amino acid decarboxylase, which also affects tryptophan metabolism.