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FOXN1
forkhead box N1
The FOXN1 gene provides instructions for a protein crucial for the proper development of the immune system, particularly T-cells, and the formation of skin structures like hair and nails. The FOXN1 gene encodes a transcription factor that plays a vital role in regulating the activity of other genes.
FOXN1 is located on the long (q) arm of chromosome 17, at band 17q11.2. Arm ratio per GRCh38 - banding schematic.
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Overview
The FOXN1 gene, also known as forkhead box N1, is a key component in human development. It produces a protein that acts as a transcription factor, meaning it controls the expression of numerous other genes. This regulatory role is particularly important for the immune system, as well as for the healthy formation of skin, hair, and nails.
What the gene does
The FOXN1 protein functions primarily as a transcription factor, binding to specific DNA regions to regulate the activity of various genes. This function is critical for several developmental processes. It guides the formation of hair follicles and supports the growth of fingernails and toenails. More critically, the FOXN1 protein is indispensable for the proper development of the thymus gland, an organ located behind the breastbone. Within the thymus, immune cells called T-cells mature and become fully functional. These T-cells are essential for recognising and combating foreign invaders like viruses and bacteria, thereby preventing infection. Research also suggests a possible role for the FOXN1 protein in the development of the central nervous system, including the brain and spinal cord, although its specific role is not yet fully understood.
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Chromosome location
The FOXN1 gene is situated on chromosome 17, specifically at the 17q11.2 band. This location indicates its position on the long arm of chromosome 17. The gene provides instructions for synthesising a protein composed of 648 amino acids.
Protein structure
The FOXN1 protein has a complex domain architecture, which includes several key functional regions. It features a Fork-head (DNA binding) domain spanning amino acids 271-367, which is crucial for its function as a transcription factor. Additionally, the protein contains multiple Disordered regions at positions 1-105, 392-445, 458-508, and 623-648. These disordered regions often play roles in protein-protein interactions and regulatory functions.
Key variants
Genetic variants in the FOXN1 gene can impact its ability to produce a functional protein, potentially leading to altered gene regulation. Such changes may affect the development of the immune system, hair, and nails. At least one documented variant (Arg255Ter or R255X) leads to premature termination of the protein, preventing production of a functional FOXN1 protein.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.1370del | p.His457fs | Pathogenic | ★★★☆ | T-cell immunodeficiency, congenital alopecia, and nail dystrophy |
c.1376C>A | p.Ser459Ter | Pathogenic | ★★★☆ | T-cell immunodeficiency, congenital alopecia, and nail dystrophy |
c.1465del | p.Gln489fs | Pathogenic | ★★★☆ | T-cell immunodeficiency, congenital alopecia, and nail dystrophy |
c.246C>A | p.Cys82Ter | Pathogenic | ★★★☆ | T-cell immunodeficiency, congenital alopecia, and nail dystrophy |
c.340C>T | p.Arg114Ter | Pathogenic | ★★★☆ | T-cell immunodeficiency, congenital alopecia, and nail dystrophy |
c.562del | p.Ser188fs | Pathogenic | ★★★☆ | T-cell immunodeficiency, congenital alopecia, and nail dystrophy |
c.723C>G | p.Tyr241Ter | Pathogenic | ★★★☆ | T-cell immunodeficiency, congenital alopecia, and nail dystrophy |
c.880G>A | p.Val294Ile | Pathogenic | ★★★☆ | T-cell immunodeficiency, congenital alopecia, and nail dystrophy |
c.933_936dup | p.Asp313fs | Pathogenic | ★★★☆ | T-cell immunodeficiency, congenital alopecia, and nail dystrophy |
c.958C>T | p.Arg320Trp | Pathogenic | ★★★☆ | T-cell immunodeficiency, congenital alopecia, and nail dystrophy |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Pathogenic variants in the FOXN1 gene are associated with an inherited condition characterised by T-cell immunodeficiency, congenital alopecia, and nail dystrophy. This condition impacts the immune system's ability to function effectively and also affects the growth and structure of hair and nails. Research indicates that variants in FOXN1 can disrupt normal protein function, leading to these features.
No disease links recorded for this gene in our reference set.
Inheritance pattern
Conditions caused by pathogenic FOXN1 variants typically follow autosomal recessive inheritance.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
UK clinical status
The FOXN1 gene is included in several UK NHS clinical panels, reflecting its established role in health. It is listed on the COVID-19 research panel, the DDG2P (Deciphering Developmental Disorders) panel, and the Primary immunodeficiency or monogenic inflammatory bowel disease panel (R15), all with a 'green' status indicating a strong evidence base for its involvement in these conditions.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What is the primary function of the FOXN1 gene?
The FOXN1 gene provides instructions for creating a protein that acts as a transcription factor. This protein is essential for the development of the immune system, particularly T-cells, and the normal growth of hair and nails.
How do variants in FOXN1 affect health?
Variants in the FOXN1 gene can impair its function, leading to a condition characterised by T-cell immunodeficiency, congenital alopecia (hair loss), and nail dystrophy. This impacts both immune system function and the development of hair and nails.
Is the FOXN1 gene associated with inherited conditions?
Yes, the FOXN1 gene is associated with an autosomal recessive inherited condition that affects the immune system, hair, and nails. Individuals inherit a copy of the altered gene from each parent to be affected.
References
- Vigliano I, Gorrese M, Fusco A. FOXN1 mutation abrogates prenatal T-cell development in humans. Journal of medical genetics. 2011. PMID: 21507891
- Amorosi S, Vigliano I, Del Giudice E. Brain alteration in a Nude/SCID fetus carrying FOXN1 homozygous mutation. Journal of the neurological sciences. 2010. PMID: 20864124
- Pignata C, Fusco A, Amorosi S. Human clinical phenotype associated with FOXN1 mutations. Advances in experimental medicine and biology. 2009. PMID: 20429426
- Amorosi S, D'Armiento M, Calcagno G. FOXN1 homozygous mutation associated with anencephaly and severe neural tube defect in human athymic Nude/SCID fetus. Clinical genetics. 2008. PMID: 18339010
- Adriani M, Martinez-Mir A, Fusco F. Ancestral founder mutation of the nude (FOXN1) gene in congenital severe combined immunodeficiency associated with alopecia in southern Italy population. Annals of human genetics. 2004. PMID: 15180707
- Pignata C. A lesson for unraveling complex aspects of novel immunodeficiencies from the human equivalent of the nude/SCID phenotype. Journal of hematotherapy & stem cell research. 2002. PMID: 11983112