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HPRT1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

HPRT1 gene

The HPRT1 gene is responsible for producing an enzyme that recycles purines, and its dysfunction leads to severe neurological and behavioral conditions known as Lesch-Nyhan syndrome.

Normal Function

The HPRT1 gene provides instructions for producing an enzyme called hypoxanthine-guanine phosphoribosyltransferase (HGprt). This enzyme allows cells to recycle purines, which are essential building blocks of DNA and RNA.

While cells can make new purines (de novo purine synthesis), this process requires significant energy. Recycling purines through the purine salvage pathway is more efficient and ensures that cells have a steady supply of building blocks for DNA and RNA production. Purines also play a critical role in providing cellular energy and facilitating cell communication, which is especially important during development.

Health Conditions Related to Genetic Changes

Lesch-Nyhan syndrome

Hundreds of pathogenic variants in the HPRT1 gene cause Lesch-Nyhan syndrome. This condition is characterized by severe movement problems, behavioral issues including self-injury (such as biting and hitting), and arthritis caused by the overproduction of uric acid. It occurs almost exclusively in boys and men.

The condition occurs when there is less than 1.5 percent of normal HGprt enzyme activity. Without enough of this enzyme, purines are not recycled but are instead broken down, leading to abnormally high levels of uric acid.

Lesch-Nyhan variant

Individuals who have pathogenic variants resulting in 2 percent or more of normal HGprt enzyme activity are considered to have Lesch-Nyhan variant or partial HPRT1 deficiency. The signs and symptoms are milder than those of Lesch-Nyhan syndrome; while affected individuals may have high uric acid levels and neurological problems, they typically do not engage in self-injury. Because both conditions are caused by variants in the same gene, they are considered part of the same disease spectrum.

Frequently Asked Questions

Management focuses on symptom control. Medications can help reduce uric acid levels, preventing kidney stones and gout. For neurological symptoms, physical and occupational therapy are vital. Behavioral management strategies, often involving protective restraints or dental guards, are used to prevent self-injury, as there are no medications that reliably stop these behaviors.
Early signs often include developmental delays, especially in motor skills like sitting up or crawling, and low muscle tone (hypotonia). As the condition progresses, involuntary movements, such as dystonia (sustained muscle contractions) and choreoathetosis (writhing movements), become noticeable. In Lesch-Nyhan syndrome, self-injurious behaviors like biting lips or fingers typically emerge in the first few years of life.
Diagnosis usually involves a combination of clinical observation of symptoms, measurement of uric acid levels in blood and urine (which are typically very high), and genetic testing to identify mutations in the HPRT1 gene. Enzyme activity assays can also measure the level of HGprt. A diagnosis helps guide management, anticipate potential complications like kidney stones and neurological issues, and allows for early intervention, though there is currently no cure.
Lesch-Nyhan syndrome is an X-linked recessive condition. This means the HPRT1 gene is located on the X chromosome. Males, who have one X and one Y chromosome, are affected if they inherit a mutated HPRT1 gene on their X chromosome. Females, with two X chromosomes, are typically carriers and usually do not show symptoms, but they have a 50% chance of passing the mutated gene to each child. Sons who inherit the mutation will be affected, while daughters who inherit it will be carriers.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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