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FGF8 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

FGF8 gene

The FGF8 gene provides instructions for making a protein essential for embryonic development, including the formation of nerve cells in the brain and the regulation of sexual development.

Normal Function

The FGF8 gene provides instructions for making a protein called fibroblast growth factor 8 (FGF8). This protein is part of a family of proteins involved in processes such as cell division, regulation of cell growth and maturation, and development before birth. FGF8 attaches (binds) to another protein called fibroblast growth factor receptor 1 (FGFR1) on the cell surface, triggering a cascade of chemical reactions inside the cell.

Starting before birth, signals triggered by FGF8 and FGFR1 are critical for the formation, survival, and migration of certain neurons in the brain. This signaling is essential for neurons that produce gonadotropin-releasing hormone (GnRH), which controls hormones directing sexual development before birth and during puberty. FGF8 and FGFR1 also play a role in olfactory neurons, which migrate to the olfactory bulb to process smells. Additionally, the FGF8 protein is found in the developing limbs, heart, ears, and eyes, where it is suspected to assist in the formation and development of these structures.

Health Conditions Related to Genetic Changes

Kallmann syndrome

Mutations in the FGF8 gene have been identified in people with Kallmann syndrome, a disorder characterized by hypogonadotropic hypogonadism (impaired production of hormones directing sexual development) and an impaired sense of smell. These mutations reduce or eliminate the protein's function, disrupting the migration and survival of olfactory and GnRH-producing neurons. Features may include:

  • Impaired or absent sense of smell
  • Delayed or absent puberty
  • Cleft lip and cleft palate
  • Bimanual synkinesis (mirrored hand movements)

Nonsyndromic holoprosencephaly

MedlinePlus Genetics provides information about Nonsyndromic holoprosencephaly.

Other disorders

Some FGF8 mutations cause a form of hypogonadotropic hypogonadism without an impaired sense of smell, known as normosmic isolated hypogonadotropic hypogonadism (nIHH). These mutations also disrupt the migration of GnRH-producing nerve cells, leading to delayed or absent puberty. It remains unclear why some mutations affect the sense of smell while others do not.

Other Names for This Gene

  • AIGF
  • androgen-induced growth factor
  • FGF-8
  • fibroblast growth factor 8 (androgen-induced)
  • HBGF-8
  • heparin-binding growth factor 8
  • HH6
  • KAL6

Frequently Asked Questions

FGF8 is essential for the survival and migration of olfactory neurons from the nose to the brain. Mutations in this gene can disrupt this pathway, leading to hyposmia (reduced smell) or anosmia (loss of smell), which is a hallmark of Kallmann syndrome. Currently, there is no cure to restore the sense of smell once the neural connections are disrupted during development. Management focuses on safety, such as using smoke detectors and checking food expiration dates, and psychological support to cope with the loss of a significant sensory input.
Yes, FGF8 mutations can be associated with other developmental anomalies because the protein is involved in the formation of limbs, heart, ears, and eyes. Some individuals may present with cleft lip and cleft palate, bimanual synkinesis (mirrored hand movements), or structural heart defects. In rarer cases, severe disruptions in FGF8 signaling can contribute to holoprosencephaly, a condition where the brain fails to divide into two hemispheres. A thorough physical examination and imaging studies are often necessary to identify any associated structural abnormalities beyond the primary endocrine and olfactory symptoms.
Mutations in the FGF8 gene can prevent the proper migration of neurons that produce gonadotropin-releasing hormone (GnRH), leading to hypogonadotropic hypogonadism where the body does not signal the gonads to produce sex hormones. This results in delayed or absent puberty. Hormone replacement therapy, such as estrogen or testosterone, can induce secondary sexual characteristics and bone maturation, but it does not restore the underlying neurological defect. For individuals who wish to conceive, specific treatments like pulsatile GnRH or gonadotropin injections may be required to stimulate fertility, as standard sex hormone replacement alone does not typically induce ovulation or sperm production.
FGF8-related Kallmann syndrome is typically inherited in an autosomal dominant pattern, meaning only one copy of the altered gene is sufficient to cause the condition. If one parent has the mutation, there is a 50 percent chance of passing it to each child. However, variable expressivity is common, meaning that even if a child inherits the mutation, their symptoms may range from mild to severe, or they may have no symptoms at all. Genetic counseling is recommended for family planning to understand the specific inheritance pattern and potential outcomes.
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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