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HSD17B3 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

HSD17B3 gene

The HSD17B3 gene provides instructions for producing an enzyme essential for the conversion of androstenedione into the male sex hormone testosterone.

Normal Function

The HSD17B3 gene provides instructions for making an enzyme called 17-beta hydroxysteroid dehydrogenase 3. This enzyme is active in the male gonads (testes), where it helps to produce the male sex hormone testosterone from a precursor hormone called androstenedione.

Health Conditions Related to Genetic Changes

17-beta hydroxysteroid dehydrogenase 3 deficiency

More than 20 mutations that cause 17-beta hydroxysteroid dehydrogenase 3 deficiency have been identified in the HSD17B3 gene. In the Arab population of Gaza, where the condition is most common, almost all affected individuals have two copies of the same mutation. This mutation replaces the protein building block (amino acid) arginine with the amino acid glutamine at protein position 80 (written as Arg80Gln or R80Q).

Mutations in the HSD17B3 gene result in a 17-beta hydroxysteroid dehydrogenase 3 enzyme with little or no activity, reducing testosterone production. A shortage of testosterone affects the development of the reproductive tract in the male fetus, resulting in the abnormalities in the external sex organs that occur in 17-beta hydroxysteroid dehydrogenase 3 deficiency.

Genomic Location

The HSD17B3 gene is found on chromosome 9.

Frequently Asked Questions

This deficiency primarily affects male development. At birth, affected individuals typically have external genitalia that are ambiguous, meaning they are not clearly male or female. They might have a small penis, a scrotum that is split or underdeveloped, or testes that have not descended. In some cases, the external genitalia may appear more female-like. During puberty, individuals with this condition, if not diagnosed and treated, may not develop typical male secondary sexual characteristics like a deepened voice, facial hair, or increased muscle mass, and may instead develop some breast tissue.
17-beta hydroxysteroid dehydrogenase 3 deficiency is an autosomal recessive condition. This means that an individual must inherit two copies of the mutated HSD17B3 gene (one from each parent) to develop the condition. If both parents are carriers (meaning they each have one normal gene and one mutated gene but do not show symptoms themselves), there is a 25% chance with each pregnancy that their child will inherit two mutated copies and be affected, a 50% chance the child will be a carrier like the parents, and a 25% chance the child will inherit two normal copies and not be affected or a carrier. Genetic counseling can provide detailed risk assessments.
Diagnosis often begins with a physical examination of the external genitalia, especially in newborns with ambiguous genitalia. Further evaluation involves blood tests to measure hormone levels, particularly testosterone and its precursors like androstenedione. A high ratio of androstenedione to testosterone can be indicative of the deficiency. Genetic testing of the HSD17B3 gene is the definitive way to confirm the diagnosis by identifying specific mutations.
Treatment typically involves hormone replacement therapy, specifically testosterone, to promote the development of male secondary sexual characteristics during puberty and to address any related health issues. Surgical interventions may also be considered to correct ambiguous genitalia, often performed in childhood, depending on the assigned gender and family's wishes. Genetic counseling is also important for affected families to understand the inheritance pattern and risks for future pregnancies.
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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