Similar term(s): Phenylketonuria, homozygote for PKU, heterozygote for PKU.


A hereditary genetic disease involving liver enzyme deficiency.

Source: GreenFacts


A person with PKU is completely or nearly completely deficient of the enzyme phenylalanine hydroxylase found in the liver. This enzyme is able to convert the essential amino acid phenylalanine to another amino acid called tyrosine.

Without this enzyme (phenylalanine hydroxylase), the conversion cannot take place and if action is not taken to control the intake of phenylalanine, it will accumulate in the blood and body tissues. This is a concern as chronic high levels of phenylalanine and some of its breakdown products can have effects on the brain.

As an essential amino acid, phenylalanine can only be obtained from protein in the food we eat. People with PKU can limit the intake of phenylalanine by limiting the amount of high protein foods they eat. They thus avoid eating meat, fish, poultry, eggs, cheese, milk, dried beans and peas.

As some phenylalanine is required for normal growth, a diet is required where some phenylalanine is present but in much lower amounts than normal. Phenylalanine free formulas are available but a controlled diet can be followed where cereals, starches, fruits, and vegetables are eaten and a milk substitute is used.

Phenylketonuria (PKU) is a hereditary disease, that is, to have it you need to inherit it from your biological parents. People who inherit PKU from both parents are homozygote for PKU and display all the symptoms listed above. Approximately, 1 individual in 10,000 is homozygote for PKU.

People who inherit PKU from only one parent are heterozygote for PKU, and are carriers for PKU. Carriers do not have symptoms of the disorder, they are healthy but can pass the gene on to their children.

Source: GreenFacts

Related words:

Chronic - Enzyme(s) - Heterozygous for PKU - Homozygous for PKU - Phenylalanine - Tissue

To read about this term in context:

GreenFacts Summary on Aspartame:


Español: PKU
Français: PCU (Phénylcétonurie)

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