INFORMATION FOR WOMEN WHO HAVE MATERNAL PHENYLKETONURIA DURING PREGNANCY OR BREASTFEEDING

What is phenylketonuria?

Phenylketonuria (PKU) is a recessive genetic condition, meaning that you have the condition if you received two gene copies that cause the same defect, one copy from your mother and the other from your father. Normally, the two gene copies encode an enzyme called phenylalanine hydroxylase (PAH). This enzyme is needed to convert the amino acid phenylalanine into a different amino acid, called tyrosine, which can be utilized by the body to make proteins, and also converted into still other amino acids, by other enzymes. More than 500 mutations making the gene for PAH defective have been identified. A combination of any two defective genes for this enzyme in the same individual leads to PKU but, depending on the particular mutations, the individual may have some amount of enzyme activity. If PKU is identified early in infancy, its effects can be minimized with a special diet that limits the amount of phenylalanine that you ingest.