What is Phenylketonuria (PKU)?

Phenylketonuria (PKU) is a rare genetic disorder where your body can't break down some proteins in food. If you have PKU, having a regular diet containing protein will cause damage to your brain.

What are the symptoms of PKU?

Newborns with PKU rarely have symptoms right away. Sometimes they may be sleepy or eat poorly.

If not treated, phenylalanine builds up in their blood over time. This can lead to complications. Symptoms of the build-up of phenylalanine may include:

• hyperactivity and seizures
• nausea and vomiting
• lighter skin, hair, and eyes than family members
• eczema-like rashes
• aggressive or self-harming behaviour
• emotional disturbances including anxiety
• a musty odour in sweat or urine

In some cases, the build-up can lead to mental health problems.

Early diagnosis and treatment help babies grow and develop normally like other healthy children.

What causes PKU?

PKU is a genetic disorder caused by a faulty gene passed down from both parents.

Normally, your body breaks down protein into smaller parts called amino acids. Amino acids are used for growth, repair, and body functions.

If you have PKU, your body can't break down a certain amino acid (phenylalanine) properly. This leads to a build-up of phenylalanine that can cause serious harm, especially to the brain.

When should I see my doctor?

You should see your doctor if you or your child have PKU and:

• you develop any symptoms
• you are unwell, have a fever or diarrhoea
• you stop your diet or any prescribed supplements
• you are pregnant

How is PKU diagnosed?

PKU is diagnosed through a routine newborn screening test. In Australia, all babies are tested for PKU shortly after birth using a blood sample taken from a heel prick.

If you have a family history of PKU, a prenatal test can check if your baby is affected. Parents and siblings can also be tested to see if they carry the PKU gene. If both parents are carriers, there is a 1 in 4 chance their child will have PKU.

How is PKU treated?

If your baby is diagnosed with PKU, they will need to follow a strict low-protein diet. Your doctor will refer you to a metabolic clinic that will guide you. They will advise you on the diet and monitor your baby's needs.

Regular blood tests will monitor phenylalanine levels. Treatment usually continues for life.

Diet

Phenylalanine is a normal part of a healthy diet for people without PKU. People with PKU need to follow a diet low in phenylalanine. This means avoiding high-protein foods such as meat and milk. Instead, you will eat special low-protein foods. Fruits, vegetables, and certain grains are allowed in small amounts.

Newborns start with a measured amount of special formula. As they grow, they can eat certain low-protein foods.

If you have PKU and are planning a pregnancy, it's important to strictly follow low-phenylalanine diet to protect your baby's health.

Medicine

Some medicines can help manage PKU, but they are not always available. Doctors may also recommend supplements to help manage the condition.

Living with PKU

Living with PKU means carefully managing your diet to avoid foods high in protein. Here are some tips on how to manage your diet:

• Follow a low-protein diet as directed by your doctor or dietitian and take special supplements as prescribed to ensure your diet is balanced.
• Count the protein in your food daily to avoid too much phenylalanine.
• Avoid artificial sweeteners like aspartame that contain phenylalanine. Look for additives 951 and 962, and for a warning on the label saying that the product 'contains phenylalanine'.
• Regularly check your blood phenylalanine levels to adjust your diet as needed.
• Seek advice from your healthcare team and attend all scheduled check-ups.

What are the complications of PKU?

If not diagnosed and treated early, high levels of phenylalanine in the blood from PKU can cause developmental delays in the first year of life. This can lead to neurological complications such as:

• intellectual disability
• poor coordination
• severe brain damage

Even with good dietary control, some children still may develop mild mental health problems. They may also have difficulties in school.

Children born to mothers with high phenylalanine levels during pregnancy are at risk of having a small head (microcephaly). They may also develop developmental problems. This is known as maternal PKU.

Can PKU be prevented?

PKU cannot be prevented because it is a genetic disorder. However, the risk of complications may be reduced by following a strict low-protein diet.

Resources and support

To learn more and connect with PKU support services:

• The PKU handbook — a guide for understanding and managing PKU.
• The protein counting list — a tool to help track protein intake for those on a PKU diet.
• The Metabolic Dietary Disorders Association (MDDA) offers support, services, and resources to educate and connect families living with PKU.

The Pregnancy, Birth and Baby video call service allows you to speak face-to-face with a maternal child health nurse. Video call is a free service and is available from 7am to midnight (AET), 7 days a week (including public holidays).

You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available 24 hours a day, 7 days a week.

Looking for information for Aboriginal and/or Torres Strait Islander people?

Find an Aboriginal Community Controlled Health Organisation (ACCHO) or affiliate near you.