PKU (phenylketonuria, from “phenyl”, “ketone”, “uria”, aka phenylalanine hydroxylase deficiency) is an inherited error of amino acid metabolism, where protein-rich foods or the sweetener aspartame can act as poisons, impairing metabolism of the amino acid phenylalanine.

Patient information

What is PKU? It sounds a bit like pee-ka-boo?
PKU is an inherited disease. It's where you can't metabolize a particular amino acid, called phenylalanine. It means that foods with that, like the sweetener aspartame, can act as POISONS .

What's phenylalanine? Don't they have a warning about that in bubble gum ?
Yeah they do, sugar free Wrigley's , so that's the sweetener aspartame being used. So phenylalanine is an amino acid. There are 22 amino acids, so there aren't that many of which 9 are essential. Phenylalanine is one of the essential ones. So amino acids are like your leucine, lysine, arginine, that sort of thing.

• It is an inherited disease. Both parents must be carriers of the mutated PAH gene. Most parents who are carrier causes no medical problems. To be affected by PKU, a child must inherit 2 mutated alleles, 1 from each parent
• There is absent (or virtually absent) PAH (phenylalanine hydroxylase) enzyme activity
• PAH breaks down excess phenylalanine from food
• Phenylalanine is a necessary part of the human diet, and is naturally present in all kinds of dietary protein. It is also used to make aspartame, which is used to sweeten low calorie and sugar free soft drinks, yogurts and desserts
• Although phenylalanine is a necessary part of diet, if there isn't enough PAH enzyme (or its cofactor), then excess phenylalanine from the protein in foods build up in the blood and brain, beyond what is needed in the body, to toxic levels, affecting brain development and function

• Strict phenylalanine-restricted diet, which should be maintained for life
• Supplementation by a medical formula containing amino acids and other nutrients

• Early Dx (see newborn screen), and maintenance of a strict diet, can have a normal life span with normal mental development
• Can lead to intellectual disability, seizures, and other serious medical problems

• Rare, but important to identify, because if caught early it is very treatable