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FOXN1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

FOXN1 gene

The FOXN1 gene provides instructions for making a transcription factor essential for the development of the skin, hair, nails, and the immune system.

Normal Function

The FOXN1 gene provides instructions for making a protein that attaches (binds) to specific regions of DNA and regulates the activity of other genes. On the basis of this action, the FOXN1 protein is called a transcription factor.

The FOXN1 protein is important for the development of the skin, hair, nails, and immune system. Studies suggest that this protein helps guide the formation of hair follicles and the growth of fingernails and toenails. The FOXN1 protein also plays a critical role in the formation of the thymus, which is a gland located behind the breastbone where immune system cells called T cells mature and become functional. T cells recognize and attack foreign invaders, such as viruses and bacteria, to help prevent infection.

Researchers suspect that the FOXN1 protein is also involved in the development of the brain and spinal cord (central nervous system), although its role is unclear.

Health Conditions Related to Genetic Changes

T-cell immunodeficiency, congenital alopecia, and nail dystrophy

At least one mutation in the FOXN1 gene has been found to cause T-cell immunodeficiency, congenital alopecia, and nail dystrophy, a condition that affects the immune system and the growth of hair and nails. The known mutation, written as Arg255Ter or R255X, replaces the protein building block (amino acid) arginine with a signal to stop protein production. No functional FOXN1 protein is produced from the mutated gene.

  • Immune System Impact: A lack of FOXN1 protein prevents the formation of the thymus. Without this gland, the immune system cannot produce mature, functional T cells to fight infections, leading to recurrent serious infections starting early in life.
  • Physical Characteristics: Loss of the FOXN1 protein prevents the formation of hair follicles, leading to an absence of hair (alopecia). Additionally, a shortage of this protein causes malformations of the fingernails and toenails (nail dystrophy).
  • Central Nervous System: Researchers have described abnormalities of the central nervous system in at least two cases of this condition, though it is not yet known if this is a common feature or how a shortage of the protein contributes to these findings.

Frequently Asked Questions

The thymus is the organ where T cells mature and learn to distinguish between foreign invaders and the body's own tissues. Without a functional thymus, the immune system cannot produce mature T cells, leading to severe T-cell immunodeficiency. This leaves the child highly susceptible to recurrent, severe, and potentially life-threatening infections from bacteria, viruses, and fungi, often starting in infancy.
Parents and clinicians often look for the absence of hair and abnormal nail development as primary indicators. In affected infants, the scalp may appear smooth and shiny with no visible hair shafts, and the fingernails and toenails may be thin, brittle, or completely absent. These dermatological features are typically present at birth or become apparent within the first few months of life, distinguishing this condition from other immune disorders that may present later with infections.
This condition is inherited in an autosomal recessive pattern, meaning a person must inherit two mutated copies of the FOXN1 gene, one from each parent, to develop the disease. Parents who carry one mutated copy are typically carriers and do not show symptoms. If both parents are carriers, there is a 25 percent chance with each pregnancy that the child will inherit the condition, a 50 percent chance the child will be a carrier, and a 25 percent chance the child will inherit two normal gene copies.
Currently, there is no cure for the genetic mutation itself, and the condition is serious due to the high risk of fatal infections. Management focuses on aggressive treatment of infections and maintaining immune health. In severe cases, a hematopoietic stem cell transplant (bone marrow transplant) may be considered to restore immune function, though this is a complex procedure with significant risks. Regular monitoring by an immunologist is critical for early detection and management of complications.
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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