Transient tyrosinemia of the newborn

Transient tyrosinemia of the newborn (also known as transient neonatal tyrosinemia or transient hypertyrosinemia of the newborn) is a benign, self-limiting metabolic condition characterized by elevated levels of the amino acid tyrosine in the blood during the neonatal period. It is the most common disorder of tyrosine metabolism and is considered a developmental phenomenon rather than a true genetic disease. The condition results from the delayed maturation of 4-hydroxyphenylpyruvate dioxygenase (4-HPPD), an enzyme involved in the tyrosine degradation pathway in the liver. It is more frequently observed in premature infants and those receiving high-protein diets. Most affected newborns are asymptomatic, and the condition is often detected incidentally through newborn screening programs that measure blood tyrosine levels. When symptoms do occur, they may include lethargy, poor feeding, and prolonged jaundice. Rarely, mild cognitive or motor developmental concerns have been reported, though the clinical significance of these associations remains debated. The condition primarily affects the hepatic metabolic system, and elevated tyrosine levels typically normalize spontaneously within the first few weeks to months of life. Treatment, when indicated, is generally conservative and includes dietary modification such as reducing protein intake and ensuring adequate vitamin C supplementation, as ascorbic acid is a cofactor for the affected enzyme. In the vast majority of cases, the prognosis is excellent, with complete resolution of the biochemical abnormality without long-term sequelae. It is important to distinguish transient tyrosinemia of the newborn from more serious hereditary forms of tyrosinemia (types I, II, and III), which require specific medical management and have different long-term outcomes.

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