Phenylketonuria

Phenylketonuria or often called PKU, is a rare congenital metabolic disorder. People who have PKU, are missing an enzyme in their liver that allows for amino acid break down. Because the amino acids are not broken down, they accumulate in the tissue and brain, interfering with brain development.

Some amino acids are still needed for normal growth and so PKU treatment concentrates on limiting the amount of amino acids a person consumes. 

Untreated PKU can result in mental retardation, failure to thrive and autism-like behavior. The severity of this condition varies. PKU dietary restriction is continued for life.  


Phenylketonuria and its Impact on Breastfeeding

  • Babies with PKU are more prone to developing thrush infections. 
  • Babies with PKU can still be breastfed, in-fact those that were breastfed, were found to score 12.9 points higher on the IQ scale. 
  • Breast milk contains much less amino acids than commercial formulas. Phenylalanine-free formulas can be taken while the mother continues to breastfeed. Breast milk can be given after formula feeds or in-between formula feeds. 
  • It is essential that the mother and partner contact a dietician and lactation consultant who have experience in managing PKU. 
  • If PHE levels are found to be high, the mother might need to stop breastfeeding for 1 -3 days for levels to return to normal. The mother should pump her milk during this time to maintain her milk supply. 
  • The amount of formula will need to be calculated in addition to the time spent at the breast to determine the right amount of PHE required. This amount will also change as the baby gets older. 
  • Solids are introduced according to a strict PKU diet. Rice and wheat are usually avoided completely. Aspertame should be avoided as well; it is sometimes found in artificial sweeteners, drinks, mediation and some foods.

A list of PKU support groups


Raising a Child with PKU


The Impact and Importance of PKU Screening Tests

Children born with PKU have very low, or no enzyme, that the body needs to process protein. The foods that most people eat every day are actually dangerous for them. Too much protein can cause brain damage. Anything that we consider to be a protein source, is too much for them.

Because of newborn screening, PKU is caught early enough to avoid the terrible side effects. By following a special diet for their whole life, the mental impact of PKU can be prevented.

Before newborn screening, children with PKU were undiagnosed, until they later began falling behind their peers. These children where deeply affected by severe mental disabilities and suffered throughout their lives.

Because of the screening tests that were introduced in 1961, children with PKU can now lead normal lives, to be who they would have been without PKU.


Tracy Behr, CBC, CLD (CBI)

Reference: Breastfeeding course information through Childbirth International on the physiology of breastfeeding / health problems / Phenylketonuria.

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