Phenylketonuria (PKU) is a type of amino acid metabolism disorder. It is inherited. If you have it, your body can't process part of a protein called phenylalanine (Phe). Phe is in almost all foods. If your Phe level gets too high, it can damage your brain and cause severe intellectual disability. All babies born in U.S. hospitals must now have a screening test for PKU. This makes it easier to diagnose and treat the problem early.
The best treatment for PKU is a diet of low-protein foods. There are special formulas for newborns. For older children and adults, the diet includes many fruits and vegetables. It also includes some low-protein breads, pastas and cereals. Nutritional formulas provide the vitamins and minerals you can't get from their food.
Babies who get on this special diet soon after they are born develop normally. Many have no symptoms of PKU. It is important to stay on the diet for the rest of your life.
NIH: National Institute of Child Health and Human Development