What Are the Symptoms of Phenylketonuria?

Medically Reviewed on 1/27/2023
Symptoms of Phenylketonuria
Phenylketonuria is a hereditary disorder that cannot be prevented or avoided.

Phenylketonuria (PKU) is most commonly characterized by psychological or behavioral issues, stunted growth, and skin conditions (such as an eczema-like rash).

The symptoms of PKU can range from moderate to severe. It may take six months for the early signs to develop.

Symptoms of PKU may include:

  • Seizures
  • Hyperactivity
  • Tremors or shaking
  • Irritability
  • A musty odor in breath, skin, or urine
  • Intellectual disability
  • Defects in the heart
  • Loss of interest in the surroundings
  • Small sized head
  • Lighter skin tone, hair, and eye color

A newborn with typical PKU may seem normal for the first several months of life. If an early diagnosis is not established in the infant at birth and left untreated in the early stages, this condition can cause:

  • Irreversible brain damage, which can impair intellectual abilities within the first few months of life.
  • Behavioral issues and episodes of seizure attacks in older children.

What is phenylketonuria?

Phenylketonuria (PKU) is a genetic disorder caused by a defect in the gene responsible for the formation of the enzyme, phenylalanine hydroxylase. This enzyme metabolizes a necessary amino acid, phenylalanine, and in the absence of this enzyme, phenylalanine accumulates in the body.

Amino acids are the building blocks of proteins. Phenylalanine is found in all proteins and certain artificial sweeteners. The enzyme phenylalanine hydroxylase converts phenylalanine to tyrosine. Tyrosine help produce neurotransmitters, such as adrenaline, norepinephrine, and dopamine. Phenylalanine converts into melanin, a pigment that gives color to the skin, hair, and eyes.

An excess level of phenylalanine in the body is toxic to the nervous system and causes serious complications, such as:

  • Brain damage
  • Prevent growth and development of the brain
  • Mental retardation
  • Other serious health issues including:

How is phenylketonuria diagnosed?

It is crucial to diagnose the presence of phenylketonuria (PKU) even before the symptoms appear to provide appropriate treatment and prevent serious complications. The diagnosis of PKU is rarely missed in the screening procedure. People of any age with developmental delays or intellectual disabilities are often tested for PKU.

The incidence of PKU is high in the United States and among Native Americans. All newborns in the United States are routinely tested for the presence of phenylalanine hydroxylase in the blood.

  • Routine blood and urine tests are done on newborns. If those tests detect the presence of excess levels of phenylalanine hydroxylase enzyme, the diagnosis of PKU is confirmed.
  • PKU can potentially be identified before the child’s birth. A pregnant woman can seek genetic testing to determine whether the unborn child will be affected by the condition. This is accomplished by amniocentesis or chorionic villus sampling. This testing could be beneficial if the parents already have one kid with PKU. They have a higher-than-normal chance of having another kid with the disease.

How is phenylketonuria treated?

Treatment should be initiated immediately after diagnosis with phenylketonuria (PKU).

The severity of your child's condition or blood levels will determine the therapeutic approach.

  • Diet
    • A low-protein diet is the initial line of treatment.
    • All high-protein foods (such as meat, eggs, and dairy products) must be excluded from the diet, as well as restricting many other items, such as potatoes and cereals.
    • Infants may require a specific formula to limit the quantity of protein they consume.
    • An amino acid supplement and protein intake are necessary to ensure enough nutrients and proper growth and health.
    • Specifically designed diets with low-protein foods, including flour, rice, and pasta. Following such diets for life will help prevent symptoms of PKU.
    • If people with PKU follow a low-protein diet and keep their phenylalanine levels under certain ranges, they will be healthy and their intellectual ability will be unaffected.
  • Medications
    • No treatment cures the condition, and the ultimate cure is achieved through a liver transplant.
    • The FDA recently approved the drug sapropterin for the treatment of PKU. Sapropterin helps reduce phenylalanine levels.
    • This drug must be used in combination with a PKU food plan.
    • However, it may not work for everyone with PKU, but it works well in children with mild symptoms of PKU.
    • Children diagnosed with PKU require lifelong symptomatic treatment and monitoring to prevent complications.

Can you prevent phenylketonuria?

Phenylketonuria (PKU) is a hereditary disorder that cannot be prevented or avoided. It is an autosomal recessive condition passed on from parent to child, both parents must have a mutant version of the PAH gene for the child to acquire the disease. The child will not get PKU if just one parent has the mutant gene.

Having a mutant gene in both parents does not mean their child will develop PKU; there is a 25 percent risk that the carrier parents will both pass down the faulty gene, causing the child to have PKU.

Medically Reviewed on 1/27/2023
Image Source: iStock image

What is Phenylketonuria (PKU)? https://www.chp.edu/our-services/rare-disease-therapy/conditions-we-treat/pku

Phenylketonuria (PKU) in Children. https://www.stanfordchildrens.org/en/topic/default?id=defects-in-metabolism-of-amino-acids-pku-160-58