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Princess Margaret Hospital
WA Newborn Screening Program - Information For Parents
Phenylketonuria (PKU)
What is PKU?
PKU is an amino acid disorder. It is a hereditary disease that is caused by a missing enzyme needed to digest phenylalanine. Phenylalanine is an amino acid that is present in all foods containing protein. Without treatment, phenylalanine builds up in the blood and causes brain damage and mental retardation.
What Causes PKU?
The gene defect for PKU is inherited when both parents have the same abnormal gene and unknowingly pass it on to their baby. A parent who has the abnormal gene, but not the disease, is called a carrier. The health of a carrier is rarely affected. However, for each pregnancy of two such carriers, there is a 1 in 4 chance that the child will be born with the disease. PKU occurs in about 1 in every 16,000 births in WA. There are also milder forms of PKU (called hyperphenylalaninaemia) in which the blood phenylalanine levels are lower. Very rarely, a severe form of PKU occurs and is caused by a lack of biopterin, which helps in the enzymatic digestion of phenylalanine.
What Problems does PKU Cause?
Infants with PKU appear normal for the first few months. However, they then begin to lose interest in their surroundings and their development slows. Children with untreated PKU have severe mental retardation and behavioural problems and they may also have a musty odour, dry skin, rashes or convulsions. These problems can be avoided if treatment is started in the first weeks of life.
How is PKU Treated?
PKU is treated by limiting the amount of phenylalanine in the diet. Phenylalanine is found in protein containing foods. Babies who are diagnosed with PKU are put on a special milk substitute and later in life the diet is mainly vegetarian. It is recommended that the special diet be followed throughout life.
Screening Issues
The screening test measures the level of phenylalanine in the blood. For reliable screening the test should not be performed before 48 hours.
