Phenylketonuria (PKU) is a genetic disorder in which the body can't process part of a protein called phenylalanine (Phe). Phe is in almost all foods. If the Phe level gets too high, it can damage the 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 they 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 that they stay on the diet for the rest of their lives.
NIH: National Institute of Child Health and Human Development