Therefore, the research study has several objectives. These are to investigate the impact KuvanTM therapy has on (1) body composition parameters of PKU patients: such as lean body mass, percent body fat, bone density, weight gain, and growth (2) dietary changes, and the effect of those changes, on intake of calories and essential nutrients (3) changes in blood biomarkers of certain nutrients (4) blood and urine neurotransmitter levels, since these changes could indicate improved neurological functioning, (5) and quality of life of PKU patients, who may feel less burdened due to the dietary freedom KuvanTM provides.