Hi I am 40 and have PKU. It was thought back when I was 7 that the brain had fully developed and that going off the diet was okay. They didn’t realize the damaging effects it would have on me. I was off the diet for over 30 years and have gone back on the diet. I see a big difference in my life and my abilities. I didn’t go back on my diet until I realized that I was having problems multi tasking as well as patience, and remembering. It was like I was living life in a fog. But since I got back onto my diet and controlled my phe levels. I have been out of my fog and normal again. So my suggestion is to not go off your diet. It doesn’t do you any good and I am living proof of that.