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5-minute read

Key facts

  • Phenylketonuria is a rare, treatable, inherited disorder.
  • All babies born in Australia are screened for PKU.
  • Babies diagnosed with PKU will develop normally in every way, as long as they keep to a strict, low-protein diet all their life.
  • If you have PKU, eating a regular diet containing protein will cause damage to your brain.

What is Phenylketonuria (PKU)?

Phenylketonuria (PKU) is a rare, treatable disorder where your body cannot break down foods containing protein. If you have PKU, having a regular diet that contains protein will cause damage to your brain.

What causes PKU?

PKU is an inherited condition caused by a faulty gene. If you have PKU both your parents must carry this faulty gene.

If you are healthy, when you eat protein, your body will break it down in stages, first into building blocks called amino acids. Then the amino acids will then be broken down further and used by your body for growth, functioning and repair.

If you have PKU, your body can’t break down an amino acid called phenylalanine normally.

What are the symptoms of PKU?

Because screening for PKU occurs in all newborn babies, it is treated early in those who have it. This means it is rare for symptoms to occur in people who have PKU.

However, if you have PKU and you have a regular diet that includes protein, phenylalanine can build up in your body to harmful levels.

High levels of phenylalanine can cause cell changes inside the brain. This may lead to severe brain damage. It may also lead to a delay in the physical and intellectual development of those whose brains are still maturing. This may result in irreversible intellectual disability, seizures or behavioural abnormalities.

Early diagnosis of PKU is critical since the brain is developing rapidly in the first 2 years of life.

How will my baby be diagnosed with PKU?

PKU is diagnosed through routine newborn infant screening. All babies born in Australia are tested for PKU soon after birth, with a blood sample taken from a needle prick to the heel.

What treatment will my baby need for PKU?

If your baby is diagnosed with PKU in the newborn screening test, they must follow a strict low protein diet their whole life. Your doctor will refer you to a metabolic clinic team who will help guide you, and advise you about the diet and monitoring your baby needs.

Phenylalanine is a normal part of a healthy diet for people without PKU, and is found in some artificial sweeteners as well as in protein. To find out whether a product contains sweeteners, check the following:

  • The ingredient list on the food label (additives 951 and 962, many artificial sweeteners and aspartame-acesulphame, contain aspartame, which is a source of phenylalanine).
  • Look for a warning on the label saying that the product ‘contains phenylalanine’. These sweeteners are used mainly in diet products such as diet drinks or yoghurts, sugar-free lollies and chewing gum.

To find out whether a product contains these artificial sweeteners, check the PKU handbook.

Following the special diet to avoid all sources of phenylalanine will allow your child to grow up healthily and with normal intelligence.

Where can I find resources and more information?

Click on the links below to learn more, and connect with support services and other families affected by PKU:

FIND A HEALTH SERVICE — The Service Finder can help you find doctors, pharmacies, hospitals and other health services.

ASK YOUR DOCTOR — Preparing for an appointment? Use the Question Builder for general tips on what to ask your GP or specialist.

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Last reviewed: September 2022

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