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Maternal PKU & Pregnancy: Making Every Week Count


If you are a woman with phenylketonuria (PKU), and are planning to get pregnant, or already are pregnant, this guide is for you.  Having PKU and being pregnant is known as maternal PKU. While planning a pregnancy and when you are pregnant, staying completely on your diet and taking the formula is essential for the health of your baby as well as your own health.  During your pre-pregnancy planning and your pregnancy you’ll work closely with your doctor or midwife, nutritionist, and obstetrician.  Being pregnant with PKU is challenging, but with careful planning ahead of time, and with the right diet, health care, and information, you can experience the wonder and joy of carrying and delivering a healthy baby.

About PKU
About Maternal PKU
Healthy PKU Pregnancy
PKU and Genetics
Newborn Baby’s Health
PKU Nutrition & Recipes!
PKU & Pregnancy Resources
Maternal PKU Research Study

About PKU

Before talking about maternal PKU and your baby, it is important that you understand PKU and your own body. When people eat, the protein in our food is broken down into much smaller parts called amino acids. A person’s body then uses these amino acids to build other proteins that they need.  However, a person’s body does not need all of the amino acids they eat.  So, some of each amino acid is left over and must be changed to other chemicals in the body. This changing of chemicals in the body is called metabolism.

If you have the disorder called phenylketonuria (PKU),  your body is missing a special “changer” protein (enzyme) called phenylalanine-hydroxylase. Because of this your body cannot change one of the amino acids called phenylalanine (Phe) to another amino acid called tyrosine, as shown in the diagram above.  When this happens the Phe builds up in your blood and can affect your brain.  To prevent this and stay healthy, you must avoid foods that contain high levels of Phe, such as milk, cheese, eggs, fish, meat, beans, and nuts. You must also take a special formula (medical food) to replace the other amino acids that you would otherwise get from foods you must avoid. These two steps of avoiding high-Phe foods and taking the formula allow you to maintain metabolic control of your Phe levels.

How did I get PKU?

PKU is a genetic disorder that a person inherits from his or her parents.  In the cells of our bodies are tiny structures called genes, which control how different functions in the body work.  The gene involved in PKU makes phenylalanine-hydroxylase. Genes come in pairs.  So, if you have PKU, then you inherited two PKU genes, one from each of your parents. This means that each of your parents has at least one PKU gene. They each passed a PKU gene on to you, and since you received two PKU genes, you were born with PKU, as shown in this diagram:

Note: in very rare cases, one of your parents is a carrier (has one PKU gene and one normal gene) and the other parent has PKU (has two PKU genes), and they each passed a PKU gene on to you.

In people who don’t have PKU, there are two possible ways that these normal or PKU genes got passed along to them:

  • If someone inherited only one PKU gene from one parent, and a normal gene from the other parent, then they are a PKU carrier, but do not have PKU
  • If someone inherited normal genes from both parents, and did not inherit any PKU genes, then they are not a carrier and do not have PKU

How common is PKU?

One out of 12,000 babies is born with PKU in the United States and in many other countries throughout the world. Though anyone can be born with PKU, it occurs most often in people of Northern European ancestry. Ethnically Turkish people have the highest chance of getting PKU (one person in every 2600) and the Irish also have a high chance (one in 4500). However, PKU is very rare in African-American, Ashkenazi Jewish, and Japanese populations.

What are the risks and problems of having PKU?

If you have PKU and stay on diet, you are much more likely to have a healthy adult life.  If, however, you are unable to stay on diet and control your Phe levels, you may have learning disabilities and emotional issues. An uncontrolled Phe level can affect your motor control (working with your hands), spatial perception, memory, and problem solving.  Over the years it can lead to other disorders, including certain fears, anxiety, depression, attention problems, headaches, sleep disorders and antisocial behavior. These can cause problems in your work and in your relationships.  For these reasons, it is very important that you stay on diet and maintain control of your Phe levels throughout your adult life.

Are there any new or improved treatments for PKU?

Yes! New treatments may help you stay in metabolic control throughout your adult life. However, some of these new treatments do not help everyone with PKU. Additional new treatments may be available in the future. Your metabolic physician can advise you about what treatments are best for you and which are safe during pregnancy.  Here’s a summary of some new treatment options:

  • BH4 therapy: This medication can increase the activity of the enzyme (phenylalanine-hydroxylase) that does not work in people with PKU. Some people with PKU, especially those with milder forms, can lower their blood Phe levels with this medicine, and can sometimes eat more protein. BH4 is known commercially as Kuvan.
  • Large Neutral Amino Acid therapy:  This medication may help keep Phe from entering your brain.  However, this medication cannot replace diet during pregnancy.
  • Formulas: There are many new formulas (medical foods), some of which taste better than the old formulas.

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

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