A special diet is the main treatment for phenylketonuria. Medications are also available. Treatment and monitoring is lifelong.

Phenylketonuria (PKU) is an inherited condition where the amino acid phenylalanine (Phe) builds up in your body. PKU is caused by genetic mutations that reduce or eliminate your body’s ability to make the enzyme that normally breaks down Phe.

The accumulation of Phe can damage the brain and lead to intellectual disability if PKU is left untreated. Due to this, babies born with PKU need to begin treatment right away. The treatment of PKU is lifelong.

Keep reading below to learn about the different treatment options for PKU. We’ll cover the main treatment for PKU, other available treatments, and what PKU monitoring entails.

Newborn screening for phenylketonuria

In the United States, newborn screening for PKU is required in all states. The National Institute of Child Health and Human Development notes that this has practically eliminated PKU as a cause of intellectual disability in the United States.

Hospitals screen for PKU by analyzing a small blood sample collected from your baby’s heel.

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The main treatment for PKU is dietary intervention. The goals of the PKU diet are to:

  • Reduce the amount of Phe you get from food sources, which will help to limit the buildup of excess Phe in the body.
  • Ensure that other essential amino acids are obtained through the use of Phe-free or low-Phe amino acid supplementation.
  • Maintain a healthy growth and nutritional status.

Amino acids are the building blocks of proteins. Because Phe is an amino acid, it’s present in protein sources. This means that people with PKU need to adhere to a low protein, low Phe diet, which means avoiding foods like:

It’s important to keep in mind that Phe is still an essential amino acid and cannot be completely removed from your diet. Low protein versions of common foods, such as flour, rice, and pasta are also available for people with PKU.

Examples of foods that people with PKU can typically eat without limitations include:

In addition to the PKU diet, there are other treatments available. The Food and Drug Administration (FDA) has approved two drug treatments for PKU.

  • Sapropterin (Kuvan) is an oral drug that acts as the cofactor for the enzyme affected by PKU. It can stimulate residual amounts of the enzyme to break down Phe. Kuvan is used in combination with the PKU diet.
  • Pegvaliase-pqpz (Palynziq) is an injectable drug that’s made up of an enzyme that breaks down Phe. It’s used in adults who are on PKU treatment, but who still have uncontrolled high Phe levels.

People with PKU need lifetime treatment. To ensure that treatment is maintaining low Phe levels, people with PKU will need to have the levels of Phe in their blood checked periodically.

The frequency of monitoring will vary across your lifetime. Phe levels are typically monitored more closely during certain periods, such as during:

  • infancy
  • the first year of life
  • early childhood
  • pregnancy

The table below shows recommendations from the National Institute of Health for the frequency of Phe monitoring across one’s lifetime.

Life stageFrequency of Phe monitoring
newborn to age 1 yeartwice weekly to weekly
ages 1 to 7 yearsweekly to monthly
ages 8 to 18 yearsweekly to monthly
pregnancytwice weekly to weekly
postpartum lactationweekly to monthly

Recommendations vary in terms of monitoring frequency. It’s always best to work with your doctor to determine a monitoring plan that’s best for you.

In addition to regular Phe monitoring, people with PKU will also have periodic nutritional and health evaluations throughout their lifetime.

Most people with PKU go on to lead healthy lives if they follow their treatment plan. PKU doesn’t affect your life expectancy, with or without treatment. The outlook for a child is very good if they closely follow a low phenylalanine diet.

It’s best to start the PKU diet as soon as possible, within the initial 7 to 10 days of life. If a child starts and closely follows a doctor-prescribed, low phenylalanine diet within their first weeks of life, they should be able to live a normal life and not be limited intellectually or physically.

Maintaining the PKU diet can help to keep Phe levels low and prevent damage to the brain. If the diet is stopped, neurological problems can occur, including:

  • seizures
  • abnormal muscle movements
  • tight muscles
  • increased reflexes
  • involuntary movements
  • tremors

People with PKU can also go on to have healthy pregnancies. However, high Phe levels can harm a developing fetus. As such, it’s important that people with PKU adhere to the PKU diet and see their doctor for regular monitoring prior to and during their pregnancy.

PKU is an inherited condition that leads to high levels of the amino acid Phe in the body. If PKU is left untreated, its effects can cause brain damage and intellectual disability starting at a young age.

The main treatment for PKU is a special diet. Because Phe is found in proteins, this involves avoiding high protein foods and focusing on low protein or no protein foods.

Low protein foods, such as bread and pasta, and specially prepared medical foods are available for people with PKU. Medications are also approved to be used along with the PKU diet.

Treatment of PKU is lifelong. If you have PKU, it’s important to work with your doctor to manage your diet and monitor your Phe levels and overall health.