My 10 y/o daughter Amber started Kuvan 3 weeks ago. Her levels stayed at the 9-10 range on a half restricted diet (2000mg phe daily) with the kuvan her levels dropped to the 2-3 range!!!! She is definitly a responder!! We are so excited for her to start eating new foods, slowely of course.. we have also already seen a huge improvement in her behavior, learning skills, ect. Thers only one problem,,headaches almost daily. Her nutritionist says her levels may be getting too low. so we have to look at uping her phe intake, or lesson the pills. Either way i think Kuvan is going to benifeit her greatly,,but hope the headaches go away.. Anyone on Kuvan had headaches???