Phenylketonuria, also know as Folling’s Disease or more commonly PKU, is an inherited, metabolic disorder characterized by the body’s inability to produce a sufficient amount of the enzyme responsible for breaking down the amino acid phenylalanine. Left undiagnosed, the condition can lead to a variety of problems which range in severity from irritability, eczema and vomiting to neurological deficits, seizures, and severe mental retardation. Fortunately, PKU is a manageable condition.
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Causes and Testing
An inherited disorder, a child will only develop PKU if both parents carry the gene. If both parents carry the gene but do not have PKU, their chances of having a child with the condition are 25%. If one partner is a carrier of the gene and the other has PKU, the chances increase to 50%, and in instances where both parents have PKU, all of their children will have the condition.
In the UK and the US, all infants are tested for PKU during the first month of life. A simple blood test determines the level of phenylalanine present in their system and if this level is high, a diagnosis of PKU is confirmed.
Although there is no cure for PKU, the condition is manageable through careful dietary restrictions. Foods that are high in phenylalanine must be avoided, while foods containing lower amounts of phenylalanine should be substituted. Additionally, many of those diagnosed with PKU are prescribed a phenylalanine-free protein supplement. A paediatric dietician is normally consulted to provide parents with appropriate feeding guidelines.
The naturally high levels of phenylalanine in some foods make them off limits to those with PKU. Meats, eggs, dairy and nuts are typically forbidden completely, while some fruits and starches must be consumed in limited quantities as they contain moderate amounts of phenylalanine.
The standard PKU diet replaces meat, dairy, and eggs with a special medically prescribed formula that does not contain phenylalanine. Most of the caloric needs of people with PKU are met by consuming this formula, with the remaining calories coming from eating low-phenylalanine foods, such as grains, vegetables, and some fruits. Most foods contain some phenylalanine, so those with PKU must carefully monitor their food intake to keep their blood levels within the safe range.
When infants are first diagnosed with PKU, parents are advised on proper diet. As children grow and begin to make some of their own dietary choices, they must be made aware of their limitations. When well managed, PKU will not produce negative changes within the body, but if the recommended diet is not closely followed, there will be consequences.
Studies show that if the diet is not adhered to during infancy and early childhood, irreparable brain damage and IQ loss is probable. For teens and adults with PKU, loosening the dietary restrictions may not have consequences quite as dire, but many will notice emotional and intellectual deficits. Regular blood testing throughout life is necessary to keep a close watch on the blood level of phenylalanine.