Phenylketonuria (pronounced fen-l-kee-toh-NOOR-ee-uh), or PKU, is an inherited disorder that that can cause intellectual and developmental disabilities (IDDs) if untreated.
In PKU, the body can't process part of a protein called phenylalanine, which is in all foods containing protein. If the phenylalanine level gets too high, the brain can become damaged.
All children born in U.S. hospitals are tested routinely for PKU soon after birth, making it easier to diagnose and treat early. Children and adults who are treated early and consistently develop normally.
Depending on the level of phenylalanine and tolerance for phenylalanine in the diet, PKU is classified into two different types: classic, which is the severe form, and moderate.
Children with untreated PKU appear normal at birth. But by age 3 to 6 months, they begin to lose interest in their surroundings. By age 1 year, children are developmentally delayed and their skin has less pigmentation than someone without the condition. If people with PKU do not restrict the phenylalanine in their diet, they develop severe intellectual and developmental disabilities.
Other symptoms include: behavioral or social problems; seizures, shaking, or jerking movements in the arms and legs; stunted or slow growth; skin rashes, such as eczema; small head size (microcephaly); musty odor in urine, breath, or skin that is a result of the extra phenylalanine in the body; fair skin and blue eyes, due to the body's failure to transform phenylalanine into melanin.