Abstract
One of the issues to be resolved in phenylketonuria is whether patients with mild hyperphenylalaninemia need treatment, or in other words, in what patients treatment needs to be started. Do patients need treatment when phenylalanine concentrations in blood are >360 μmol/L or >600 μmol/L? This paper reviews the literature on the outcome of untreated patients with mild hyperphenylalaninemia to try to determine whether outcome is normal. The paper concludes that there is, in fact, only one paper that can be used to answer this question. Therefore, the question is whether we may rely on one paper to draw conclusions or whether more research is necessary to determine whether all patients with phenylalanine concentrations >360 μmol/L or all patients with phenylalanine concentrations >600 μmol/L require treatment.