Phenylketonuria (PKU) is a rare but potentially serious inherited condition.
It means the body cannot process certain amino acids. Amino acids are the 'building blocks' of protein.
Someone with PKU cannot properly process the amino acid phenylalanine. This can build up in their blood and brain, leading to brain damage.
About 1 in 4,100 babies born in Ireland has PKU. With early diagnosis and treatment most live healthy lives.
Screening for PKU
Babies are screened for PKU as part of heel prick screening. They are offered heel prick screening when they are 3 to 5 days old.
If your baby has PKU
Your baby will be seen in the National Centre for Inherited Metabolic Disorders (NCIMD), Children's Health Ireland at Temple Street. They will be cared for a specialist metabolic team, including a metabolic doctor, nurse and dietitian.
Symptoms of PKU
PKU does not usually cause symptoms if treatment starts early.
Without treatment, PKU can damage the brain and nervous system. This can lead to learning disabilities.
Other long-term symptoms include:
- behavioural difficulties such as temper tantrums and self-harm
- fairer skin, hair and eyes than other family members - PKU affects melanin, which controls skin and hair colour
- eczema
- jerking movements in arms and legs
- tremors
- epilepsy
- musty smell on the breath, skin and urine
Treating PKU
Treatment for PKU involves a special diet and may also include medicine. Your baby will also need regular blood tests to monitor and adjust their diet.
Diet
The main treatment for PKU is a low-protein diet and controlled intake of other foods, such as potatoes and cereals.
If your child has PKU they will start treatment straight away.
They will need:
- a low-protein diet - this usually means avoiding high-protein foods such as meat, fish, eggs and dairy products
- protein supplements - for normal growth and good health
A specialist metabolic dietitian will make a detailed plan for your child. This will change as your child grows and their needs change.
It is recommended your child stays on treatment for life.
Aspartame
Aspartame is an artificial sweetener. People with PKU must avoid food products with aspartame. It is converted to phenylalanine in the body.
Aspartame is found in:
- sugar substitutes - people often use these in tea and coffee
- diet versions of fizzy drinks
- chewing gum
- squashes and cordials
- some children's cold and flu medicine
Always check food and medicine labels for aspartame.
Breastfeeding your baby
Some breastfeeding is possible for babies with PKU, but it will be limited. Your dietitian will advise you on this.
You can feed your baby regular infant formula, but this may need to be restricted. You may be offered a special PKU formula to supplement your baby's needs.
Medicine
Your baby may be given a medicine called sapropterin. If it works for them, it can help your baby break down phenylalanine.
Regular blood tests
If a child has PKU, they will usually need regular blood tests throughout their life.
How a child inherits PKU
PKU is caused by a gene change passed on by both parents. The parents are usually carriers and do not have symptoms themselves.
If you're a carrier of the gene and you have a baby with someone who is also a carrier, your baby has a:
- 1 in 4 chance of having PKU
- 1 in 2 chance of being a carrier of PKU
- 1 in 4 chance of receiving a pair of normal genes
PKU and pregnancy
Women with PKU have to take special care during pregnancy. This is because high levels of phenylalanine can harm an unborn baby.
The metabolic team will be able to offer you support and advice.
If your levels of phenylalanine are controlled, problems can be avoided. You can have a healthy baby.
It's recommended that you plan your pregnancy carefully. Follow a strict diet and check your blood twice a week before trying to become pregnant. You should try to conceive when phenylalanine levels are within the target range for pregnancy.
Contact your GP or dietitian as soon as possible if you get pregnant when your phenylalanine levels are not well controlled.
If your levels come down within the first few weeks of pregnancy, the risk of complications to your baby is low.
More information
You can get more information about PKU at the National Centre of Inherited Metabolic Disorders.
Patient and family information and support - metabolic.ie
To speak to a metabolic doctor contact CHI at Temple Street.
Phone: (01) 878 4200