Phenylalanine hydroxylase mutations with corresponding in vitro predicted residual enzyme activities (PRA) used for subsequent analysis
| Mutation | Activity (% of normal) |
| R243X, R252W, R408W, F299C, IVS12nt1, IVS10nt546 | 0 |
| E280K | 3 |
| R158Q | 10 |
| I65T, L348V, R261Q | 30 |
| Y414C | 50 |
| R408Q | 55 |