Since its discovery, there have been many advances in its treatment. It can now be successfully managed by the patient under ongoing medical supervision to avoid the more serious side effects. If, however, the condition is left untreated, it can cause problems with brain development, leading to progressive mental retardation, brain damage, and seizures. Early cases of PKU were treated with a low-phenylalanine diet. More recent research has now shown that diet alone may not be enough to prevent the negative effects of elevated phenylalanine levels. Optimal treatment involves maintaining blood Phe levels in a safe range while monitoring diet and cognitive development. There is no cure for PKU, but patients who are diagnosed early and maintain a strict diet can have a normal life span with normal mental development.