Phenylketonuria and Sleep

Phenylketonuria and Sleep

Phenylketonuria (PKU) is a rare metabolic disorder caused by mutations in a gene that cells use to make an enzyme. This enzyme converts an amino acid called phenylalanine into another amino acid called tyrosine.

Without the enzyme necessary to process it, phenylalanine builds in the body, causing this disease’s known symptoms. But several other molecules that are dependent on tyrosine for their production also go lacking. The loss of these molecules, particularly, can affect your ability to sleep.

How can PKU affect sleep?

In PKU, mutations in the PAH gene reduce the levels of an enzyme called phenylalanine hydroxylase (PAH), which normally converts phenylalanine into tyrosine. The body uses tyrosine to build a number of different neurotransmitters, including dopamine, serotonin, and norepinephrine. All of these are involved in the sleep cycle. Another molecule with a role in the sleep-wake cycle, called melatonin, is produced from serotonin.

One study in adults with PKU compared the incidence of sleep disorders between 25 patients and 23 of their first-degree relatives (all healthy). Four questionnaires were given participants to assess sleep disorders and difficulties. Results showed that 48% of PKU patients had scores indicating disturbed sleep, as did 19% of their healthy relatives. A poorer quality of sleep and more daytime sleepiness was also evident among patients compared with their relatives.

A separate study compared 32 children with PKU with 32 healthy children as controls. It found low serotonin  levels in 43.8% of the PKU children and low melatonin levels in 43.3% of them. Differences in sleep quality between these two groups were not evident, however, on the basis responses to a single questionnaire. The researchers noted that the effects of age on sleep disorders in PKU patients has not been studied.

Tips for better sleep

If you or your child has PKU and is experiencing sleep disorders, here are some tips that may help.

Controlling phenylalanine levels

One way to possibly improve sleep is to make sure that phenylalanine levels are under control. Limiting phenylalanine and increasing tyrosine can help make sure that the body is producing adequate amounts of necessary neurotransmitters.

The most common way of regulating phenylalanine levels is through diet.  Treatments with Kuvan or Palynziq may also be helpful in lowering phenylalanine levels for some patients.


Research has shown that people with PKU often have lower than normal melatonin levels. Melatonin is an integral to regulating sleep-wake cycles.

If you are lacking melatonin, taking melatonin tablets as a supplement may help in restoring your sleep rhythm. Always talk to your primary physician before starting any medication, including supplements.

Other suggestions

Your healthcare provider may be able to prescribe medications, or to modify medications you are using that might be causing sleep issues.

Some lifestyle changes can also be helpful. Exercise during the day is know to help improve sleep. Setting a specific sleep schedule can also help. Avoid or limit time spent watching television, or using cell phones and computers in the evening, as the blue light their screens emit can interfere with asleep. Also avoid alcohol, nicotine, caffeine, and large meals in the evenings. Reducing stress through meditation, and reading a book, taking a warm bath, or using calming fragrances such as lavender can also help.


Last updated: March 4, 2021


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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