Nongenetic causes of hypertyrosinemia that must be considered when interpreting a finding of elevated urinary tyrosine

In several countries newborns are screened for tyrosinemia type 1 using tyrosine as a primary marker . In some situations elevated tyrosine levels in blood are discovered due to elevated tyrosine in a metabolic urine screening. In Peru, some pediatric patients suspected of having a genetic condition (inborn error of metabolism) undergo a metabolic urine screening that includes - among other things - qualitative detection of tyrosine. However, when there are elevated levels of tyrosine in urine this does not always mean that the patient has a genetic condition. Most often hypertyrosinemia has a non-genetic origin. Therefore, it is important to review the non-genetic causes of hypertyrosinemia and thus avoid potential misinterpretations of this finding. The genetic entities associated with increased levels of tyrosine are those that generate an enzymatic deficiency in the degradation of tyrosine, within which tyrosinemias type I, II or III are included (2,3). However, elevated tyrosine levels in the blood usually have a nongenetic cause. The most common non-genetic cause of increased tyrosine levels in the blood is transient tyrosinemia of the newborn. This is due to immaturity of enzymes involved in tyrosine degradation– such as 4-hydroxyphenylpyruvate dioxygenase– such as 4-hydroxyphenylpyruvate dioxygenase.