Phenylketonuria (PKU) is an inherited disorder of metabolism where the body can’t process a portion of the protein called phenylalanine (Phe), which is in almost all foods. If the Phe level gets too high, the brain can become damaged.

Phenylketonuria is an autosomal recessive genetic disorder.

Children with untreated PKU may appear normal at birth. By age three to six months, they begin to lose interest in their surroundings. By age one year, they are developmentally delayed and their skin has less pigmentation than someone without the condition. If Phe is not restricted in the diet, those with PKU develop severe intellectual and developmental disabilities (IDDs) including:

  • Problems with brain development
  • Progressive mental retardation
  • Brain damage
  • Seizures

Optimal treatment involves lowering blood Phe levels to a safe range and monitoring diet and cognitive development. Lowering of phenylalanine levels to a safe range may be achieved by combining a low-phenylalanine diet with protein supplements. People with PKU who are on this diet from birth or shortly thereafter develop normally and often have no symptoms of PKU.

Pregnant women who know they have PKU need to keep good control of the level of Phe in their diets beginning before and continuing throughout pregnancy. High levels of Phe in the blood can cause developmental problems and birth defects (such as small brain size and heart defects) in the fetus.

The PKU diet includes:

  • Fruits
  • Vegetables
  • Some low-protein breads, pastas, and cereals

There is also a special formula, made without Phe, that people with PKU drink to help them get the vitamins and minerals they can’t get from their food.

Generally, people with PKU can’t eat high-protein foods, such as meat, milk, eggs, and nuts. It is recommended that people with PKU stay on the diet for life to promote overall health and to prevent decline in mental function.