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JAG1 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

JAG1 gene

The JAG1 gene provides instructions for making the Jagged-1 protein, which is essential for cell signaling during embryonic development and throughout life.

Normal Function

The JAG1 gene provides instructions for making a protein called Jagged-1, which is involved in an important pathway by which cells can signal to each other. The Jagged-1 protein is inserted into the membranes of certain cells. It connects with other proteins called Notch receptors, which are bound to the membranes of adjacent cells. These proteins fit together like a lock and its key.

When a connection is made between the Jagged-1 and Notch proteins, it launches a series of signaling reactions (Notch signaling) affecting cell functions. Notch signaling controls how certain types of cells develop in a growing embryo, especially cells destined to be part of the heart, liver, eyes, ears, and spinal column. The Jagged-1 protein continues to play a role throughout life in the development of new blood cells.

Health Conditions Related to Genetic Changes

Alagille syndrome

At least 226 mutations in the JAG1 gene have been identified in people with Alagille syndrome. Most of these mutations result in an abnormally short Jagged-1 protein that is missing the segment that normally spans the cell membrane (the transmembrane domain). Other mutations interfere with proper transport (trafficking) of the protein within the cell, preventing it from reaching the cell membrane.

The loss of Jagged-1 protein at the cell membrane precludes its interaction with Notch proteins and prevents cell signaling. The lack of Notch signaling causes errors in development that result in:

  • Missing or narrowed bile ducts in the liver
  • Heart defects
  • Distinctive facial features
  • Changes in other parts of the body

People with JAG1 gene mutations may have one or more of these problems. In particular, some affected individuals have a particular combination of heart defects known as tetralogy of Fallot without other signs or symptoms of Alagille syndrome. The type and severity of problems associated with Alagille syndrome may differ even within the same family.

Cancers

Increased activity (expression) of the JAG1 gene has been linked to certain cancers, including breast cancer and head and neck tumors. The increased expression of the JAG1 gene may promote the development of new blood vessels that nourish a growing tumor. The altered gene expression may also enhance other cancer-related events such as cell division (proliferation) and the inflammatory response.

Other Names for This Gene

  • AGS
  • AHD
  • AWS
  • CD339
  • CD339 antigen
  • HJ1
  • JAG1_HUMAN
  • jagged 1 (Alagille syndrome)
  • jagged 1 precursor
  • JAGL1

Frequently Asked Questions

Mutations in JAG1 usually produce a shortened or mis‑folded Jagged‑1 protein that cannot reach the cell surface to interact with Notch receptors. Without proper Notch signaling, the developmental programs that form bile ducts in the liver and the cardiac outflow tract are disrupted, leading to narrowed bile ducts (cholestasis) and congenital heart defects such as pulmonary artery stenosis.
JAG1-related Alagille syndrome is inherited in an autosomal‑dominant pattern, meaning each child of an affected parent has a 50 % chance of inheriting the mutated gene. However, disease severity varies widely; some carriers have mild or no symptoms, while others develop the classic multi‑system features. Genetic counseling and testing are recommended before family planning.
Management focuses on relieving cholestasis and preventing complications: ursodeoxycholic acid to promote bile flow, fat‑soluble vitamin supplementation (A, D, E, K), and monitoring for portal hypertension. In severe cases, surgical options such as biliary drainage or liver transplantation may be considered. Regular cardiac follow‑up and ophthalmologic exams are also part of comprehensive care.
confirmed pathogenic JAG1 mutation often eliminates the need for invasive liver biopsy to establish the diagnosis of Alagille syndrome. Biopsy may still be performed if the clinician needs detailed information about liver fibrosis stage or to rule out other liver diseases, but many centers rely on genetic testing combined with clinical criteria.
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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