My son will be 6 in November. We started the Kuvan a week ago. So far no changes in his blood work. I am so happy for those of you that show so much of a jump in phe you are able take in. My son is considered hyper phe (depending on the dr). His levels are about 4.6 and takes in about 500mg phe per day. I am cautiously optomistic about the kuvan since they say it only works in about half the cases of pkuers. I will keep everyone posted as to our experience.