What is Phenylketonuria?
Phenylketonuria (PKU) is a rare inherited disorder that causes an amino acid called phenylalanine to build up in the body. PKU is caused by a change in the phenylalanine hydroxylase (PAH) gene. This gene helps create the enzyme needed to break down phenylalanine. Without the enzyme necessary to break down phenylalanine, a dangerous buildup can develop when a person with PKU eats foods that contain protein or eats aspartame, an artificial sweetener. This can eventually lead to serious health problems.

Signs and symptoms
Signs and symptoms of untreated PKU can be mild or severe and may include a musty odor in the breath, skin or urine, neurological problems that may include seizures, skin rashes, such as eczema, lighter skin, hair and eye color than family members, because phenylalanine can’t transform into melanin, small head size, hyperactivity, intellectual disability, delayed development, behavioral, emotional and social problems or mental health disorders.

Children with Phenylketonuria
Babies born to women with high phenylalanine levels don’t often inherit PKU. But a child can have serious problems if the level of phenylalanine is high in the mother’s blood during pregnancy. Newborns with PKU initially don’t have any symptoms. However, without treatment, babies usually develop signs of PKU within a few months.

Diagnosis of Phenylketonuria
Babies in many countries are screened for PKU soon after birth. Although there is no cure for PKU, recognizing PKU and starting treatment right away can help prevent limitations in areas of thinking, understanding and communicating (intellectual disability) and major health problems. Overall, people with PKU — babies, children and adults — need to follow a diet that limits phenylalanine, which is found mostly in foods that contain protein. Newer medications may allow some people with PKU to eat a diet that has a higher or an unrestricted amount of phenylalanine.

Sources and useful links:
Mayo Clinic