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PKU facts

About PKU for newborn babie

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The heel prick test carried out on our newborn baby shows high blood Phenylalanine (Phe) levels. Does this mean he/she has Phenylketonuria (PKU)?
Typically babies are screened for PKU shortly after birth with the Guthrie heel prick test. Blood Phenylalanine (Phe) levels are measured and if the result is high, further tests are carried out to confirm or exclude PKU. The period between birth and diagnosis is too short to affect the brain.
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Do people with Phenylketonuria (PKU) emit a special odour?
Untreated, children with classic PKU may secrete a musty odour as a side effect of excess Phenylalanine (Phe) in the body. They are also more prone to skin disorders such as eczema.
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Are there any outward signs of the disorder?
With proper management, there are no obvious signs of PKU. The possible exception is lighter complexion and lighter hair due to a deficiency in Tyrosine, an amino acid found in protein.

Treatment information for newborn babies with PKU

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Can babies with Phenylketonuria (PKU) be breastfed? Or do they need to be bottle fed?
No. It’s still possible to safely breastfeed your baby, usually after he or she has taken his/her prescribed Phe-free formula. Your baby can then breastfeed naturally until satisfied. Ask your PKU specialist for advice.
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Do I need to give my baby more of the special Phenylalanine (Phe)-free formula if I do not breastfeed?
No. Babies who are not breastfed are given standard infant formula in addition to the special formula. How much is determined by regular blood testing for Phe levels. All babies are different. The precise amount of Phe a child with PKU can tolerate varies from one baby to the next, just as it varies as your child develops.
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How do I know if my newborn baby is hitting the right Phenylalanine (Phe) targets?
Your PKU specialist will be able to advise you on the correct blood Phe targets and will provide you with a special Phe-free prescription. The prescription will be regularly adjusted as your baby grows. For further insight, see Establish your blood Phe range.
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How does prescription formula differ from standard formula?
Babies with Phenylketonuria (PKU) receive a special formula that contains every amino acid found in protein except Phenylalanine (Phe). There are 20 amino acids that are considered standard, and of those, 10 are essential to a healthy diet because the body cannot produce them. Among these ‘essential amino acids’ is Phe.

Manage your life for newborn babies with PKU

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Can I prepare my baby’s formula myself?
Yes. Your dietitian or nutritionist will teach you how to accurately mix and properly store formula. Expect your baby’s prescription to change frequently in relation to growth and development. For further information see Preparing your baby’s formula.
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If I breastfeed, do I need to follow a special diet?
No, but do try to follow a balanced diet to maintain your own health and fitness. Your PKU specialist will be able to answer further questions about your child’s disorder treatment management.
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Are babies with Phenylketonuria (PKU) more vulnerable to other illnesses too?
Babies with PKU are no more or less prone to illnesses or infections than other infants. If your child is unwell, contact your family doctor just as you would if your child didn’t have PKU. Remind him/her that your child has PKU.
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Is it safe to leave my baby in the care of a babysitter, who has no prior knowledge of PKU?
Yes, so long as they are they are properly briefed about your baby’s disorder and understand his/her dietary restrictions. Download the guide What to tell your child’s carer

About PKU for children

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I thought protein was only contained in food like meat, chicken, fish and dairy products. Why can’t my child eat carbohydrates like bread and pasta?
Phenylalanine (Phe) is found in some foods that aren’t generally thought of as containing protein, for example, most wheat products such as pasta and bread, and some fruit such as oranges and cherries.
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Apart from prescribed supplements or substitutes, what drinks can I give my child?
Encourage your child to drink water. Too much juice and other sweet drinks may create weight issues and problems for his/her teeth. Your dietitian or nutritionist will be able to advise how frequently your child can have other drinks.
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Are there any other special precautions I should take with my child’s health?
No. Children with PKU are no more vulnerable to typical childhood illnesses than other kids and should undergo routine immunisations. You should be aware however that during illness, blood Phenylalanine (Phe) levels might rise due to protein breakdown in the body, regardless of blood Phe management.

Treatment information for children with PKU

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The diet prescribed for my child seems so extreme. Is there an alternative to help our child reach Phenylalanine (Phe) targets?
Yes. Some children are able to take medication from the age of four, which may help them maintain blood Phe at a low level and within a target range. Your PKU specialist will be able to able to perform a test to determine if your child is eligible for medication and inform you about practical, related aspects of treatment.
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The thought of having to calculate Phenylalanine (Phe) in food and take blood samples is overwhelming. How will I cope?
Caring for a child with Phenylketonuria (PKU) is a big challenge, but one you’ll rise to with guidance from the team of PKU specialists who’ve been assembled to help you along the way. If ever you feel unsure, contact your dietitian or nutritionist to ask for advice and speak with other parents who understand what you’re going through. Discover an entire network of support in our Directories.
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What happens if my child accidentally eats food high in Phenylalanine (Phe)?
Phenylketonuria (PKU) is unlike some food allergies that produce an immediate visible and physical reaction. High blood Phe levels are toxic to the brain, but build over time. Make sure you record the amount and kind of food your child has eaten and if you’re unsure about how to redress his/her dietary balance that day, consult your dietitian or nutritionist for advice.

Manage your life for children with PKU

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My child, who has Phenylketonuria (PKU), seems to need more trips to the dentist than my other children. Is there a connection with PKU?
Kids with PKU are at greater risk of dental decay because sugary food and acidic drinks may be consumed more often to boost energy. Ask your dentist whether your child should use full-strength fluoride toothpaste. Also, excessive consumption of sugary or acidic food and drinks should be avoided. Your dietitian or nutritionist will be able to give you further advice.
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Do sports have any positive effect on blood Phenylalanine (Phe) levels?
Everyone needs exercise, especially a developing child. Sport alone will not lower blood Phe levels and offset a diet high in Phe. However, exercise that helps build muscle may increase your child’s blood Phe tolerance level over time.
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As a baby it was easy to control my child’s diet but now my child has contact with other children. I worry that he will eat something he shouldn't.
As your child becomes more independent, it’s not possible to be with him/her every minute of the day. The best protection you can offer is to educate your child from an early age about the foods he/she can eat and to ensure carers and other parents who may have temporary responsibility are aware of the risks. For further information see Laying the foundations for a healthy, independent future and download the guide What to tell your child’s carer.

About PKU for teenagers

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Do I need to have my blood Phenylalanine (Phe) levels tested so often now that I am older?
During teenage years, Phe testing usually takes place twice a year. If you have reason for concern in between, arrange to see your PKU specialist.
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I exercise daily. Does this mean I can relax my diet a little?
A lengthy exercise workout will not lower blood Phenylalanine (Phe) levels if you’ve eaten too much protein in one sitting. However, exercise that helps build muscle may increase your blood Phe tolerance level over time.
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How can stick out my diet now I’m at secondary school? The other kids already treat me like a freak.
Deciding who to speak to openly about Phenylketonuria (PKU) isn’t easy. But your friends, your real mates, will want to know more about your disorder and how they can help. It may be a word of encouragement when you need it most. Talk to them and remember it’s individual differences that make us the people we are.

Treatment information for teenagers with PKU

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Why are my blood Phenylalanine (Phe) levels higher than they were a couple of years ago before I hit my teens?
Kids achieve better blood Phe control than teenagers, largely due to the support they receive from their parents. Eighty percent of young adults have blood Phe levels higher than their target level compared with twenty-five percent of children5. If you’re struggling, see your PKU specialist to discuss treatment support. You may be able to benefit from a synthetic form of BH4 known as Sapropterin Dihydrochloride, which may help you maintain blood Phe at a low level and within a target range.
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Does taking medication mean I can stop my diet?
Because there are so many different defects possible in the PAH (Phenylalanine Hydroxylase) enzyme, not everyone with Phenylketonuria (PKU) will be helped. Research shows that people with mild and moderate PKU show the greatest response. However some people with severe PKU also respond. Your PKU specialist will be able to perform the appropriate test to determine if the medication will work for you.

Manage your life for teenagers with PKU

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When I’m out with my friends, are there drinks I should avoid?
Once you turn 18 years of age, be aware that beer, wine and any other alcohol contain Phenylalanine (Phe), as do reduced calorie foods with the sugar substitute aspartame.
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My school is organising a trip abroad. I want to go, but it’s such a hassle not being able to eat the same as everyone else.
A trip away does involve some planning. Find out as much as you can about the places you’ll be visiting, particularly any restaurants or hostels where you may be staying. Most professional kitchens are used to accommodating special dietary needs. Check whether you’ll have access to a microwave or fridge to prepare some meals yourself. Go to If you’re taking a trip for more tips.
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I haven't had my blood Phenylalanine (Phe) levels tested for a while and I feel like everything is getting too much.
Taking responsibility for your disorder management is tough. And you know enough about Phenylketonuria (PKU) to understand what happens when you ignore blood Phe level targets. You experience mood swings and your concentration wavers. If you’re unsure if your diet is on track, check in with your PKU specialist to arrange a blood sample. Go to When to arrange a blood sample to check your blood Phe levels for further information.
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The thought of having to stick to a diet all my life is depressing and I'm scared.
The support network that helped guide your family through your childhood still exists. Becoming independent, accepting responsibility for your health isn’t something you need do alone. Your PKU team of specialists, dietitians or nutritionists will always be there to back you up. For further support visit the PKU directories.

About PKU for adults

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My blood Phenylalanine (Phe) levels are higher than usual. Could it have anything to do with a virus I’ve just shaken off?
During periods of illness, remember that no matter what you do, blood Phe levels will increase somewhat. This happens as a result of the body’s response to illness, which involves the breakdown of body protein.
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I struggle with some of the disorder management tasks performed regularly, like blood tests. Are the blood samples being collected accurately?
If you’re unsure about how to collect your blood samples at home, make an appointment to see your PKU team to check you’re following the correct procedure or visit Taking blood samples at home. Alternatively, appointments to collect blood may also be made at your local hospital or clinic.
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Do I still need to maintain a food diary?
Maintaining a food diary helps your dietitian or nutritionist gain insight into your dietary habits. Diaries of all food and beverages consumed are usually kept for three-days at a time. Your PKU team can then make adjustments to your supplement or substitute prescription to ensure blood Phe targets are met.

Treatment information for adults with PKU

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I don’t want to change my diet. Is there any way around it?
New approaches to PKU management may help you maintain blood Phe at al low level and within a target range. Ask your PKU specialist about a personalised treatment program.
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Is medication an option for everyone?
Your PKU specialist will be able to perform the appropriate test to determine if the medication will work for you. Because there are so many different defects possible in the Phenylalanine Hydroxylase (PAH) enzyme, not everyone with Phenylketonuria (PKU) will be helped. Research shows that people with mild and moderate PKU show the greatest response. However some people with classic PKU also respond.
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Can I just take medication?
The full range of treatment options includes low Phe diet, medication and supplements or substitutes. Your PKU specialist will be able to advise you on the best treatment plan to achieve your individual blood Phe target levels.

Manage your life for adults with PKU

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I have not followed a special PKU diet for years. I don’t even remember how to count protein. Have I left it too late?
It’s never too late to resume a Phenylalanine (Phe)-restricted diet. Make an appointment to see your PKU specialist and discover how advances in treatment programs which may help you maintain blood Phe at a low level and within a target range.
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A friend is arranging a special celebration dinner. I don’t want to offend her by not going or refusing to eat her meal. Any suggestions?
There’s no right or wrong way to handle the situation, but special occasions will always run more smoothly if plans are made in advance. Explain your dilemma to your friend. She may be able to accommodate your dietary needs within the planned menu or offer to make a contribution to the meal yourself.
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I don’t have the time or energy to prepare a homemade meal low in Phenylalanine (Phe) every day.
You could try devoting part of your weekend to preparing some meals in advance. Divide the portions into appropriate sizes; label them with the date and store them in individual containers in the freezer. You can also measure out appropriate portions of breakfast cereal and store those in airtight containers too.

About PKU for pregnancy

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I’ve grown up with Phenylketonuria (PKU) but never fully understood the risks of pregnancy. I am now pregnant. Is it too late to help my unborn child?
High levels of Phenylalanine (Phe) in your blood expose the developing foetus to the serious likelihood of brain damage. See your PKU specialist immediately to discuss what treatment options exist to lower your blood Phe levels.
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Our firstborn child was diagnosed with Phenylketonuria (PKU). What is the likelihood that our next child will also have the disorder?
If both parents carry one faulty PKU gene there is a 25% chance that your child will be born with the disorder.
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My neighbour has a child with Phenylketonuria (PKU), even though no one else in the family has the disorder. Sometimes I worry about my unborn child. Is there a test I should have?
Testing for possible carrier status in a family with no history of PKU is difficult and not always accurate. Discuss testing with your PKU specialist or a genetic counsellor.

PKU treatment information for pregnancy

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How much time should be allowed to achieve a healthy pregnancy?
Before falling pregnant, visit your PKU specialist to ensure that you’re doing everything you can to lower your blood Phenylalanine (Phe) levels. Ideally, you should reach and maintain a blood Phe level of 2 mg/dl (120 µmol/l) during the six months preceding conception9.
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Can I continue medication during pregnancy?
Women with Phenylketonuria (PKU) who maintain good control of their blood Phe levels before and during pregnancy stand an excellent chance of a normal neonatal outcome. However achieving this degree of control requires major commitment and support. Your PKU specialist will be able to advise on treatment options to help maintain optimum blood Phe levels. Evaluations are made case-by-case as to whether medication should continue during pregnancy.
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How often are blood tests required during pregnancy?
It’s likely your Phenylalanine (Phe) blood levels will be monitored twice a week to ensure they remain safe.

Manage your life with PKU for pregnancy

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I stopped the special PKU diet years ago. But now I want to get pregnant and worry that I’ve ruined my chances of a healthy pregnancy. What should I do?
Make an appointment to see your PKU specialist. For the best chance of a normal neonatal outcome, ideally you should reach and maintain a blood Phenylalanine (Phe) target level set by your PKU specialist six months preceding conception. It’s never too late to start again. Your PKU specialist will be able to advise on treatment options to help maintain optimum blood Phe levels.
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How do I ensure my unborn child receives the right nutrients during pregnancy?
Consult your dietitian or nutritionist for advice on whether you should follow a special diet in the months ahead. Your PKU specialist will also be able to advise whether you are suitable to take medicine, which may help you to meet your blood Phenylalanine (Phe) levels.
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I have Phenylketonuria (PKU) and my pregnancy wasn’t planned and I am scared my child could be born with severe disabilities. Who can I speak to?
Each day an unborn child is exposed to high maternal blood Phenylalanine (Phe) levels can cause damage to the developing foetus. See your PKU specialist immediately and ask about genetic counselling regarding the risks and outcome to your unborn child.

General information about PKU

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What is Phenylketonuria (PKU)?
Phenylketonuria or PKU is a rare inherited disorder, which affects the body’s ability to break down an amino acid called Phenylalanine (Phe) found in foods containing protein. High Phe may trigger brain-related problems throughout life. In infants, the disorder leads to irreversible damage of the developing brain without dietary management. In adults, higher blood Phe levels may lower intelligence and response times; lead to irritability, anxiety and depression; result in an inability to focus or pay attention and cause eczema.
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How common is PKU?
A diagnosis of the disorder occurs in about 1 in 10,000 Caucasian or East Asian births. Some ethnic groups have lower rates, like the Japanese, (1 in 143,000) and some higher, such as the Irish, (1 in 4,500) and Turkish, (1 in 2500). PKU is rare among Africans. For more information see Ethnicity as a factor
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What kind of health specialist should I see to find out more about Phenylketonuria (PKU)?
If your newborn child has received a diagnosis of PKU, your initial contact may be with a PKU specialist or a paediatrician with special knowledge of PKU. Over time, your clinic or hospital may refer you to other specialists, including dietitians and nutritionists.

General information about PKU treatment

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How can I find a list of suppliers of special food or supplements or substitutes?
Your dietitian or nutritionist will be able to supply you with a list of local suppliers. For further information about suppliers or a PKU association in your area, visit PKU directories.
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Is medication part of a treatment option available for everyone?
Your PKU specialist will be able to perform the appropriate test to determine if the medication will work for you. Because there are so many different defects possible in the Phenylalanine Hydroxylase (PAH) enzyme, not everyone with PKU will be helped. Research shows that people with mild and moderate PKU show the greatest response. However some people with classic PKU also respond. Your PKU specialist will be able to inform you about practical, related aspects of treatment. The full range of treatment options include: Phe-free food, supplements or substitutes (including LNAA), and medication.
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Can dietary restrictions be relaxed as childhood ends?
For people with Phenylketonuria (PKU), mental wellbeing involves a life-long commitment to Phe control. Up until 1970, clinicians believed that dietary treatment was only necessary until the end of childhood. It was thought that the brain was only vulnerable to the toxic effects of elevated blood Phe levels during the period of accelerated development. However with research came concerns about the safety of abandoning the diet at all ages.

General information about managing your life with PKU

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One of the kids in my class has Phenylketonuria (PKU). How can I help him?
You’re helping already, by visiting this site and increasing your personal understanding of the disorder. Most likely, the child’s parents have already provided you with information and instructions about the disorder. Remember, aside from the child’s dietary restrictions, it’s important to treat the child like any other in your class. He or she is no more vulnerable to any childhood illnesses or risks.
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I’m planning a gap year with my best friend, who has Phenylketonuria (PKU). I'm worried that her health could become an issue while we're away. Is there anything I should know about the disorder?
Ultimately her health is her responsibility, although you can provide encouragement by supporting what may at times be difficult dietary choices. Most likely she’s weighed up the challenges such a trip presents. But you may want to spend some time mapping and researching destinations where she can be sure that her dietary needs can be maintained.