Guldberg et al classified patients with phenylketonuria on the patient's ability to tolerate phenylalanine in the diet. This correlates with the activity of phenylalanine hydroxylase (PAH) activity. The authors are from multiple institutions in Europe.

Patient selection: child with hyperphenylalaninemia, typically around 5 years of age


Target for dietary phenylalanine ("tolerated"): <= 300 µmol/L


Tolerated Phenylalanine in Diet (mg per kg body weight)


Typical Phenylalanine in Diet per Day in Child

< 20 mg

classic PKU (severe deficiency PAH activity)

250-350 mg/day

20 to 25 mg

moderate PKU

350-400 mg/day

25 to 50 mg

mild PKU

400-600 mg/day


MHP (mild hyperphenylalaninemia) identifies a patient with a plasma phenylalanine concentration < 600 µmol/L on a normal diet.

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