Below is a collection of frequently asked questions regarding phenylketonuria.

  • How is PKU treated?

    It is treated successfully with a low phenylalanine diet.

  • Will my child grow normally on the special diet?

    Yes, provided you follow the diet. 

  • Will I be able to breast feed my baby?

    Yes. Breast feeding is encouraged as breast milk is relatively low in phenylalanine and it’s very good for mother and baby.  Breast feeding is used in combination with a special baby milk which does not contain phenylalanine.

  • Will my child look any different from other children?

    No. No-one will know your child has PKU unless you tell them.

  • Will my child go to main stream school?


  • Will my child grow out of PKU?

    No, your child will always have PKU as it is a genetic condition and at present there is no cure.

  • Why my baby?

    Your baby inherited PKU from you and your partner.

  • How did he/she get PKU?

    Both you and your partner carry a gene for PKU. As carriers of the gene you do not have PKU because you also have a normal gene as well as the PKU gene. We all inherit pairs of genes, one from our mother and one from our father. When both parents are carriers there is a one in four chance the baby will have PKU. If the baby inherits the gene for PKU from both parents then the baby has PKU. See The Child with PKU which explains in more detail how PKU is inherited.

  • Could PKU have been tested for before birth?

    If you have a previous child with PKU and the mutations are known then a specialist genetic laboratory can look for these mutations in future pregnancies. This can be done about 11 weeks into the pregnancy by taking a tiny piece of the placenta. It can also be done by amniocentesis later in the pregnancy. There are some risks associated with pre-natal diagnosis.

  • Did I do/eat something in pregnancy which caused my child to have PKU?

    No, there was nothing you did in pregnancy which caused your baby to have PKU.

  • Was there anything I could have done to prevent my baby having PKU?


  • Is PKU catching?

    No it is not infectious

  • Will my child be able to have children?

    Yes, but there are extra measures for women.

    See Maternal PKU leaflet.

  • Will their child have PKU?

    The chance of your child with PKU also having a child with PKU is approximately 1 in 100.

  • I have a brother/sister if they have children will they have PKU?

    It is possible that any brothers or sisters you have may also carry the PKU gene. Their partner would have to be a carrier of PKU too (1 in 50 of the population) and then the likelihood that any children they have also having PKU is 1 in 400.

  • How can I make this diet work?

    The diet does require some effort but the rewards are enormous and with the expertise of your dietitian, planning and organising, and the extensive range of foods available both on prescription and in the supermarket you will soon begin to manage it successfully. Have a positive attitude and get everyone else on board and this will help you enormously. It is a team effort!

  • What happens if my child has high levels?

    High levels are caused by eating the wrong food, illness, not enough protein substitute or lack of calories. Your dietitian will advise you how to get the levels down as soon as possible. Parents have noticed that behaviour may be affected i.e. lack of concentration, irritability or just being extra naughty.

  • What would happen if my child accidentally ate the wrong food?

    Phenylalanine levels are likely to go high. No lasting harm will occur but you should be aware that continual high blood phenylalanine levels due to eating the wrong foods will cause harm. Consistency of approach in important - so avoid bad habits.

  • How long do levels have to be high to damage my child?

    There is no definite time but frequent and prolonged high levels should be avoided to protect the brain from harm. This is one reason why you are asked to check the blood levels on a regular basis so that mistakes will be picked up.