Tyrosinuria

Tyrosinuria is the presence of tyrosine in the urine. It is a laboratory finding rather than a disease in itself and can occur when tyrosine metabolism is disrupted or when there is increased tyrosine intake or release from tissues. In many individuals it is transient or clinically insignificant; persistent tyrosinuria warrants further evaluation of metabolic or hepatic disorders.

The most clinically important causes are inherited metabolic disorders called tyrosinemias, due to deficiencies of enzymes in the tyrosine degradation pathway. Tyrosinemia types I, II, and III involve FAH, TAT, or HPD defects, respectively. These conditions can raise tyrosine and related metabolites in blood and urine and may present with liver disease, ocular or skin findings, or neurodevelopmental issues depending on the type. Tyrosinuria can also occur in non-genetic conditions such as hepatic dysfunction, renal tubular disorders, malnutrition, severe illness, or after high-protein intake. It can be transient in premature infants. Because tyrosine elevation can accompany other metabolic disturbances, the pattern of amino acids in urine and plasma helps narrow the diagnosis.

Diagnosis is established by measuring tyrosine in blood and urine, analyzing urinary metabolites, and performing genetic testing when indicated. Newborn screening programs may detect related abnormalities. Management depends on the cause; tyrosinemia type I is treated with nitisinone and dietary restriction of phenylalanine and tyrosine, with liver transplantation in severe cases.

In many patients, tyrosinuria is reversible with treatment of the underlying condition or resolves in infancy, but prognosis varies with the disorder. Regular follow-up is recommended to monitor metabolic control and organ function.