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Phenylketonuria (PKU)

Medical information you need to know as an adult with PKU

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Overview of the Condition:

Phenylketonuria (PKU) is a rare condition in which your body cannot break down an important amino acid called phenylalanine (Phe), which is found in all protein foods. Because you can’t break down this chemical, it builds up in your body and can cause serious health problems.

Possible Medical Problems for Babies and Children:

  • All newborn babies are tested for PKU in the US.
  • Babies with PKU who do not have good treatment while growing up tend to have worse PKU-related problems later in life.
  • If a Phe-restricted diet is followed, babies will develop normally – if not, babies are at risk for mental retardation, delayed social skills, hyperactivity, seizures, skin rashes, and other medical problems.

Possible Medical Problems & Symptoms for Teens and Young Adults:

  • Depression
  • Anxiety and Panic Attacks
  • Memory loss
  • Attention difficulties
  • Aggressive or angry outbursts
  • Migraines
  • Eczema
  • Sleep problems
  • Inability to finish reading a book
  • Troubles in social relationships
  • Planning, organization and other executive functioning skills
  • Breath and skin may smell “musty”

How to Avoid Medical Problems and Complications:

  • In severe forms of PKU, follow a strict low-phenylalanine (low-protein) diet.
  • Foods to avoid include: all dairy products (products with milk in them), meat, fish, eggs, nuts, regular pastas, regular rice, and artificial sweeteners like NutraSweet (aspartame) commonly found in diet soda.
  • Your diet must also include special formulas and specially prepared low-protein foods, which supply protein building blocks and other nutrients needed to keep you healthy.
  • Your diet must be monitored by a dietician who is familiar with PKU.

New treatments for PKU:

  • BH4 therapy: This is a medication that boosts the activity of the enzyme that is not working in PKU. People with milder forms of PKU can lower their blood phenylalanine (Phe) levels and can sometimes eat more protein. Some people with classic PKU also benefit from this medicine.
  • Large Neutral Amino Acid therapy:  This is also a medication that competes with Phe transport across the blood-brain barrier.  This means that less Phe enters the brain.  Note: This medication cannot replace diet during pregnancy.
  • Formulas: There are many new formulas (medical foods), some of which taste much better than the old formulas.
  • Enzyme replacement therapy: This therapy is in clinical trials.  This means that it is not yet approved for general use.  Its safety and effectiveness are being checked

Ask your metabolic doctor or dietician for more information about these advances in therapies for PKU.

Fertility and Pregnancy:

  • Women with PKU can have healthy pregnancies and deliver healthy babies if they maintain a strict low Phe diet and take the formula before and during pregnancy.
  • Staying on diet both before becoming pregnant and throughout the pregnancy can prevent developmental problems and mental retardation in their babies.
  • Pregnancies should be handled normally but the mother should be monitored by a doctor very closely.
  • PKU is passed on to babies only when both parents carry a copy of the gene.
  • This Maternal PKU & Pregnancy guide is for women with PKU who are planning a pregnancy or are pregnant:  http://newenglandconsortium.org/for-families/phenylketonuria-pku/maternal-pku-pregnancy/

How to Get Support:


Genetics Home Reference:

PKU Toolkit:


National PKU News:

The National PKU Alliance:

Transition Toolkit (New England Consortium of Metabolic Programs)

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Genetics Referrals:

Clinical Services

Genetic Services

What Next?

Now you can fill out the Medical Health Summary, print it, and save it. This will help you keep important medical information in one place.


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This Metabolic Condition Basics guide was adapted with permission from the American College of Medical Genetics ACT Sheet

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