In case of its deficiency, hyperphenylalaninemia is observed, which leads to phenylketonuria (PKU), a disease causing mental retardation, unless treated with a low-phenylalanine diet since early ...

These phenotypic classes range from classical PKU, the most severe form of the disease with a Phe tolerance of <20 mg/kg/day, to mild hyperphenylalaninemia (MHP), with blood Phe levels of <600 ...