How Does Enzyme Replacement Therapy Work for PKU?

How Does Enzyme Replacement Therapy Work for PKU?

Phenylketonuria (PKU) is a rare genetic disorder characterized by abnormally high levels of phenylalanine (a protein building block, also called an amino acid) in the body.

There is currently no cure for PKU, but treatments are available to manage symptoms and prevent disease progression. Following a low-phenylalanine diet that restricts high-protein foods may also help with symptoms. However, some patients may require enzyme replacement therapy (ERT).

What causes PKU?

Patients with PKU have a mutation in a gene called PAH. This gene provides the genetic information necessary for cells to make an enzyme called phenylalanine hydroxylase (PAH). Mutations in the gene cause cells to make the enzyme incorrectly so it doesn’t function properly.

The role of the PAH enzyme is to break down phenylalanine. In PKU, the body can’t process phenylalanine and it builds up over time in the blood and tissues. This buildup can cause cognitive dysfunction, though researchers don’t fully understand the reasons for this.

What is enzyme replacement therapy?

Enzyme replacement therapy is a treatment that replaces the enzyme that patients can’t make enough of themselves. In the case of PKU, this is the PAH enzyme.

Palynziq, approved in 2018 by the U.S. Food and Drug Administration, is an enzyme replacement therapy developed by Biomarin Pharmaceutical that includes an engineered form of phenylalanine ammonia lyase — an enzyme that breaks down phenylalanine.

Patients take Palynziq as a once-daily injection that they can learn to do at home.

If you are on Palynziq, you may not have to maintain a strict low-phenylalanine diet, though you should consult your doctor before making any changes to your diet.

You will also need to monitor your blood levels of phenylalanine while taking Palynziq. Talk to your doctor about how frequently you will need to undergo a blood test.


Last updated: May 6, 2020


Phenylketonuria News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.

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