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What is Tetrahydrobiopterin?

By Douglas Bonderud
Updated May 17, 2024
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Tetrahydrobiopterin is a naturally-occurring nutrient that is essential in the human body. It is important as a co-factor in several enzymes required for proper mental function. The nutrient is also known as THB, BH4 and sapropterin.

This key nutrient is synthesized from guanosine triphosphate (GTP), which is used as the energy source for protein synthesis. The function of tetrahydrobiopterin is to aid in the creation of essential neurochemicals. Serotonin, adrenaline and nitric oxide (NO) are all synthesized by enzymes which cannot be created without the presence of tetrahydrobiopterin.

A lack of it, or limited production, leads to tetrahydrobiopterin deficiency. When a limited amount of the substance is present in the human body, the essential amino acid phenylalanine will begin to build up. This acid is obtained through food and is extremely common. In the body, phenylalanine is converted into phenylalanine hydroxylase (PAH), which is then made into an enzyme by its interaction with tetrahydrobiopterin. Without sufficient tetrahydrobiopterin to interact with, PAH supplies in the body will become maximized, and phenylalanine will begin to build up. Typically, this condition presents at a very young age, and results in cognition problems and motor function disorders.

There is also a genetic disorder known as phenylketonuria (PKU) which displays similar symptoms. PKU causes the body to have difficulty producing PAH, which in turn means a build up of phenylalanine. In addition, a limited amount of PAH means that there will be a limited amount of the enzyme tyrosine produced, which is created when tetrahydrobiopterin is combined with PAH. This enzyme is essential in the creation of dopamine and norepinephrine, two essential neurotransmitters. The condition was discovered in 1934 by Norwegian physician Ivar Asbjorn Folling, and it is also known as Folling's disease. In the developed world, most babies are screened for this condition at between six to 14 days of age, by means of a simple blood test.

A prescription drug known as Kuvan® has been created by the BioMarin Pharmaceutical corporation for the treatment of PKU. In the United States, the Food and Drug Administration (FDA) approved the sale of this drug on December 13, 2007. The proprietary process used to create this drug uses the salt form of tetrahydrobiopterin, and has been shown in clinical trials to lower the amount of phenylalanine levels in the blood. With the use of both drug treatments and a strict diet, PKU can usually be managed and its symptoms brought under control.

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