The Disease

The Disease

PKU is a hereditary disease which means that a child suffering from PKU has inherited the predisposition for this disease from its parents. A person only develops PKU if both parents are carriers of the genes that cause the disease. If such a coincidence occurs there is a 25% risk that a child off these parents will develop PKU. Approx. 2% of the population are carriers of this gene. Coinciding genes in the parents are often (but not always) a result of close kinship between the parents.

Consequently, this disease is a relatively rare phenomenon in the Nordic countries whereas it is seen more often in more southern countries, specifically in Arab countries where marriages between cousins are more frequent. 1 in every 10,000 newborn infants is assumed to suffer from the disease. PKU is a metabolic deficiency caused by a defective enzyme of the liver, phenylalanine hydroxylase. As a result of this defect instead of being converted to tyrosine the amino acid phenylalanine (phe) builds up in the blood and tissue.

The accumulation of phenylalanine and the insufficiency of tyrosine lead to serious mental deficiencies. Without treatment the nervous system of the child will suffer damage already within the first year of its life. Consequently, it is critical to limit the intake of phenylalanine already from birth to prevent damage of the brain. Phenylalanine is part of all proteins. Therefore the treatment consists of a strictly controlled diet. The disorder is also known as "Følling's disease" named after the Norwegian doctor Asbjørn Følling who described it in 1934.

The gene of phenylalanine hydroxylase has been located to 12q24.1. Globally, approx. 400 different mutations have been described some of which are particularly frequent in Denmark. There is good agreement between genotype and phenotype in relation to PKU. This means that it is possible to predict the outcome of the known mutations; either the severe classic PKU, mild PKU, or hyperphenylalaninaemia, HPA - a very mild mutation that often does not require treatment.

The milder of the two mutations will dominate the patient. Based on the genotypes of the Danish patient cohort, 43% should be a classic mutation of PKU, 25% a mild mutation, 7% a moderate mutation, and 17% should be HPA. 8% remain unclassified either because one or both of the mutations have not been identified or because there are no previous records of the mutation concerned.

The History

Since 1959, the treatment against PKU-related diseases has involved following a strict dietary strategy primarily aimed at avoiding proteins.


Read more about the history about the PKU treatment

The History

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