PAH and phenylketonuria: Four days after the first injection, L-Phe levels remained at normal levels (100–140 μmol/l) at a total dose of 12 or 20 mg VMO/kg, whereas in mice treated with 25 mg/kg, L-Phe levels rose to 1,144 μmol/l (Figure 4b) which corresponds closely to the defined severe phenotype of HPA or phenylketonuria.20 The observed L-Phe levels correlated well with the results in liver analysis, where only trace amounts of normal Pah transcript, PAH protein and enzyme activity could be detected at the maximal dose used (Figure 4c–e).