Evaluation of PKU Sphere in Italy

20 participants with PKU will build-up their dietary intake of PKU sphere over 2-16 weeks, depending on their level of metabolic control whilst doing so. Participants will complete a gastrointestinal specific and PKU specific questionnaire at the Baseline clinic visit and record the amount of PKU sphere taken each day. Dried blood spots are taken twice per week. Once built up to a clinically appropriate intake of PKU sphere, or after 16 weeks, participants enter a 4-week Evaluation Period. The amount of PKU sphere taken per day continues to be recorded by participants. Gastrointestinal tolerance over the preceding seven days is recorded at the end of each week. Evaluations of PKU sphere's palatability are made at the end of weeks two and four of the Evaluation Period. Dried blood spots are taken once per week. The participant attends an End of Study Visit at the clinic and the investigator decides whether they should continue taking PKU sphere.