Home Health A-Z Phenylketonuria (PKU) – Symptoms, Causes and Treatment

Phenylketonuria (PKU) – Symptoms, Causes and Treatment

Verified By Apollo Doctors March 23, 2022 3164 0

Phenylketonuria, also known as PKU, refers to a rare inherited disorder that results in the build-up of amino acid, known as phenylalanine, in the body. A defect in the gene that helps produce the enzyme required to break down phenylalanine causes this disorder. Many countries screen for Phenylketonuria (PKU) soon after a child is born, as early diagnosis helps prevent major health problems.

Introduction to Phenylketonuria (PKU)

Phenylketonuria (PKU) is a rare genetic condition causing phenylalanine (an amino acid) to build up in the body. Phenylalanine is present in all proteins and certain artificial sweeteners. Phenylalanine hydroxylase is an enzyme used by your body to convert phenylalanine into tyrosine.

Tyrosine is needed by your body to produce neurotransmitters such as dopamine, epinephrine, and norepinephrine. Phenylketonuria (PKU) occurs as there is a defect in the gene that helps produce phenylalanine hydroxylase.

As a result of this missing enzyme, the body is unable to break down phenylalanine. Thus, phenylalanine starts to build up in your body. The symptoms of Phenylketonuria (PKU) can be relieved and the brain damage can be prevented if diagnosed and treated early.

What are the Symptoms of Phenylketonuria (PKU)?

Initially, newborn babies with Phenylketonuria (PKU) do not have any symptoms. However, if this condition remains untreated, they can develop signs within a few months. They include:

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What are the Causes of Phenylketonuria (PKU)?

As PKU is an inherited condition, the main cause of Phenylketonuria (PKU) is both parents passing on a defective version of the PAH gene to their child. If only one parent passes on an altered gene, the baby will not have any symptoms. However, the baby will carry the gene.

When to See a Doctor

If a screening test shows your baby may have PKU, please consult a doctor immediately to start the treatment. Similarly, if you have a history of Phenylketonuria (PKU) and plan on getting pregnant, see a doctor to learn about the risks and preventive measures. Similarly, adults with PKU must consult their doctor to maintain a PKU diet.

Call 1860-500-1066 to book an appointment.

How Can You Prevent Phenylketonuria (PKU)?

Phenylketonuria (PKU) is a genetic condition, meaning it cannot be prevented. But an enzyme assay (a blood test that determines whether you carry the defective gene causing PKU) can be done if you plan to have children. This test can also be done when a woman is pregnant,  to screen unborn babies for Phenylketonuria (PKU). If you have Phenylketonuria (PKU), strictly following a PKU meal plan throughout your life can help prevent symptoms.

What are the Treatment Options for Phenylketonuria (PKU)?

The symptoms of Phenylketonuria (PKU) can be relieved, and complications can be prevented by following a special diet and medication.

  • Diet: The most important manner in which Phenylketonuria (PKU) can be treated is by following a special diet which limits the intake of foods having phenylalanine. Infants with PKU can be given breast milk. When they grow old enough to eat solid foods, avoid giving them foods high in protein such as eggs, chicken, cheese, beans, nuts, fish, milk, beef, etc. Following dietary restrictions and consuming PKU formula throughout their lives is essential for people with Phenylketonuria (PKU) to manage the symptoms. Please note PKU meal plans vary from one person to another. Therefore, it is important to consult a doctor or dietician.
  • Medication: Your doctor can prescribe medication to lower your phenylalanine levels. Usually, medicines are prescribed in combination with a special PKU diet. However, only consume what is prescribed since it may not work for everyone. 


People with Phenylketonuria (PKU) can lead a healthy life if they follow their PKU meal plan diligently right from birth. But, if the diagnosis and treatment get delayed, it may cause brain damage and intellectual disabilities. Therefore, consult a doctor if you have any doubts.

Frequently Asked Questions (FAQs)

What will happen if Phenylketonuria (PKU) is not treated right away?

If it is not treated early in infancy, the child will be highly likely to develop intellectual disabilities. The longer this condition remains untreated, the higher the risk.

Can a person with Phenylketonuria (PKU) have children?

Women with Phenylketonuria (PKU) can have healthy children as long as they strictly maintain their low phenylalanine diet throughout pregnancy.

Can I outgrow Phenylketonuria (PKU)?

No, you cannot outgrow PKU. You must stay on the prescribed diet your entire life. 

Verified By Apollo Doctors
At Apollo, we believe that easily accessible, reliable health information can make managing health conditions an empowering experience. AskApollo Online Health Library team consists of medical experts who create curated peer-reviewed medical content that is regularly updated and is easy-to-understand.

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