I was diagnosed as hyperphe in the early ’70s. At the time, treatment protocols dictated that children with hyperphe were on a low-protein diet only until age 3, and those with classic PKU until age 6 (there were, I understand, some doctors who advocated lifelong diet adherence even then). In the ’80s, it became clear that PKUers did better if kept on-diet for life. I was off-diet from age 3 to 32 (monitored between 3 to 6), and don’t seem to have suffered for it. HOWEVER (my standard disclaimer) – just because I did ok off-diet does NOT mean all kids with hyperphe should be off-diet. All dietary considerations need to be coordinated with doctors and nutritionists. Every PKUer is different, and what works for one won’t necessarily work for others.