Frequently Asked Questions About PKU
Q: My newborn has been diagnosed with PKU. Is that serious?
A: PKU, or phenylketonuria (pronounced fen-il-Key-to-New-ree-uh), is a serious but manageable condition.
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Q: Is the condition curable?
A: Currently there is no cure for PKU. Right now, the only way to manage the disease is through a lifelong restricted diet. With proper diet management, newborns with PKU can look forward to healthy and fulfilling lives.21
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Q: How did my newborn get PKU?
A: PKU is inherited. Both parents have to carry the PKU gene in order for a child to be born with PKU. You don’t have to actually have PKU to carry the PKU gene. If you and your partner carry the gene but don’t have PKU, there is a 25% chance that any future children you have together will have PKU. If one partner has PKU, and the other is a carrier of the gene, the chance of having a child with PKU increases to 50%; if both partners have PKU, the likelihood increases to 100%.16
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Q: Are my spouse and I responsible for our newborn’s PKU?
A: Many parents feel they are somehow “to blame” for their child’s PKU. There really is no need to feel this way. There is nothing that either you or your spouse could have done during the pregnancy to cause this. You are not responsible for the genes you inherited and possess. It’s important for you to approach PKU management with a positive attitude, and you will find there is a large community of people prepared to offer you help in doing so. Your family will join many others successfully living with PKU in the years ahead.
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Q: What exactly is PKU?
Understanding the nature of this disease is key to managing your child's condition.
PKU belongs to a class of diseases referred to as “inherited metabolic diseases,” or “inborn errors of metabolism.” Most of these diseases are rare (occurring in approximately 1 in 13,500 births) and include conditions like albinism and congenital hypothyroidism.
Metabolic diseases affect the body’s ability to perform certain chemical processes required for normal growth and development. For people with PKU this means that a certain enzyme called phenylalanine hydroxylase (PAH), is broken. This enzyme is required for the breakdown of phenylalanine (Phe), an amino acid found in foods containing protein.16 Even though they produce some working PAH, most of the PAH they produce is defective and doesn’t function the way it’s supposed to, and thus isn’t able to properly break the Phe down.
PAH is a molecule produced in the liver, which sets in motion a chemical reaction that converts Phe into another amino acid called tyrosine, or Tyr.16 For people who don’t have PKU, the liver produces enough working PAH to convert Phe into Tyr, and as a result, all the Phe is used up. For a person with PKU, Phe cannot be turned into Tyr and thus excess Phe builds up, passes into the bloodstream, and circulates throughout the body, eventually ending up in the brain. While a certain amount of Phe is essential for normal growth and development, excess Phe in the brain causes damage, particularly in very young children.
The good news is that the brain damage can be prevented.12,16 Currently, this is accomplished by restricting the amount of Phe ingested. Foods that are very high in Phe, such as meat, eggs, dairy, and nuts are avoided completely. These foods are replaced by a medical protein formula that has no Phe. Foods with moderate amounts of Phe can be eaten but in limited quantities. These foods include certain fruits and starches. Most foods have some Phe in them, meaning people with PKU must always be very careful about what they eat. Therefore, it is important for someone with PKU to track daily intake of Phe.
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Q: How is PKU managed?
A: The key to PKU management is keeping the amount of Phe in the blood within a safe range. The exact definition of a safe range is still widely debated, but the National Institutes of Health suggest that blood Phe concentrations remain between 2 mg/dL and 6 mg/dL (120 µmol/L to 360 µmol/L).12
To achieve the proper blood Phe level, PKU management involves a three-pronged approach: Record, Restrict, and Replace. A person with PKU (or the parent of a young child with PKU) must record the amount of Phe consumed; restrict the diet to low-Phe foods; and replace those high-Phe foods with low-Phe alternatives—most commonly, a regimen of Phe-free medical protein supplement.
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Q: Will my child show any symptoms?
A. When PKU is managed well, there are no overt signs or symptoms,12 with the possible exception of a light complexion. Despite the fact that PKU is a lifelong disease, people with PKU can expect to lead healthy and fulfilling lives. By keeping blood Phe levels low, excess Phe will not accumulate in the brain to cause damage.
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Q: How do I learn to properly manage my child’s PKU?
A. At first, PKU management may sound a little daunting. But relax! You can work with a registered dietician associated with a metabolic clinic who can help you decide what kind of diet your child will require. That person can give you tips for establishing a management routine. To get an idea about special low-protein recipes, check out the recipe library.
As you begin your PKU research, you will find that a wealth of resources is available, including support groups and internet-based bulletin boards for communication with other parents.
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Q: What if I don’t regulate my child’s diet closely?
A: If you don’t carefully monitor your child’s diet, your child runs the risk of having elevated blood Phe levels. Maintaining low blood Phe levels is particularly important in young children, while the brain is undergoing its most dramatic development and is most vulnerable to the neurotoxic effects of excessive Phe.22
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Q: Tell me about the Phe-free formula.
A: The PKU diet replaces meat, dairy, and eggs with a special medical formula that does not contain Phe. This formula is prescribed by a doctor at a metabolic clinic. This formula is actually the centerpiece of the PKU diet. For people with PKU, most of the calories they consume come from this formula, which may take the form of a powder mixed with drinks or as a premixed drink. The remaining calories, and all of the Phe that a person with PKU needs, come mostly from relatively low-Phe foods such as grains, fruits, and vegetables. Since most food contains some Phe, people with PKU must be cautious about what—and how much—they eat.
Remember, it’s not that your child can’t consume protein, but rather your child can’t have too much of a certain amino acid, Phe, that’s found in proteins.
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Q: How long will my child be on the restricted diet?
A: In 2000, the National Institutes of Health recommended that a person with PKU requiring dietary restriction never be taken off the special diet. This is often referred to as “diet for life.”12
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Q: What can happen if my child goes off the diet?
A: This is difficult to answer due to the way the disease can vary, both among individual people with PKU and at different stages of life. It is important to talk to your doctor about any changes to your child’s diet. If the child goes off the diet very early in life (infancy/toddler to elementary school years), he or she may suffer irreparable brain damage and IQ loss. If a child goes off the diet later in life, the symptoms may be more subtle, but they will still be present. Scientific evidence suggests that people with PKU who go off the diet at any age may suffer emotional and intellectual problems.12
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Q: Is my child more at risk for attention deficit hyperactivity disorder (ADHD)?
A: PKU varies a lot, depending on the individual. The relationship between ADHD and PKU is not completely understood but has been studied.
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Q: How will a metabolic clinic be involved?
A: When your child first tested positive for PKU, the results were sent to a lab at your local metabolic clinic to confirm a diagnosis. The staff there is now committed to helping you and your child with the management of PKU, including periodic blood testing, formula prescriptions, and dietary consultations based on feedback from you and the blood tests. As part of managing your child’s condition, you will be required to stay in close contact with the clinic.
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Q: How frequent are the Phe blood tests?
A: Your doctor will determine the frequency of Phe blood tests. In the beginning, your child may be tested rather frequently while the clinic determines the appropriate diet. Testing can occur once or twice a week until your child’s Phe levels stabilize at an appropriate level. Thereafter, testing may be required once a month until the child reaches adolescence. During adolescence through young adulthood, testing may be conducted twice a year. In adulthood, yearly testing will likely continue for life.
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Q: What’s the difference between classic PKU and moderate PKU?
A: PKU is divided into two types: classic PKU and moderate PKU. These two types refer to different levels of blood Phe. A person with moderate PKU has lower blood Phe levels than a person with classic PKU. Both classic and moderate PKU patients can suffer significant neurological damage, if untreated, although this damage is more significant in classic PKU.12
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