Although I can't offer much information from a scientific standpoint, I can tell you that I have been on Kuvan for 2 1/2 years now, and my experience has been nothing but positive. When I began Kuvan I was also told that the chances that I would respond were slim. However, my dietitian was more than happy to give me a chance to try Kuvan, because she knew we would not know for sure until after I gave it a shot. As it turned out I responded amazingly, and I have not regretted my decision.
Did your dietitian mention what serious side effects she has heard of? As far as I am concerned I have not experienced any side effects due to Kuvan.