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JAK3 gene

Janus kinase 3

Normal Function

The JAK3 gene provides instructions for making a protein that is critical for the normal development and function of the immune system. The JAK3 protein is part of a signaling pathway called the JAK/STAT pathway, which transmits chemical signals from outside the cell to the cell's nucleus. Signals relayed by the JAK3 protein regulate the growth and maturation of certain types of white blood cells (lymphocytes) called T cells and natural killer cells. In addition, JAK3 is important for the normal maturation of another type of lymphocyte called B cells. T cells, B cells, and natural killer cells attack bacteria, viruses, and fungi and help regulate the entire immune system.

Health Conditions Related to Genetic Changes

JAK3-deficient severe combined immunodeficiency

More than 50 JAK3 gene mutations have been identified in people with JAK3-deficient severe combined immunodeficiency (SCID), an impairment of the immune system that leads to repeated and persistent infections that can be life-threatening.

Most mutations in the JAK3 gene prevent the production of JAK3 protein or result in a protein that is unstable and quickly broken down. Others lead to production of a protein that cannot perform its function. Without functional JAK3 protein, certain chemical signals are not relayed to the nucleus, impairing lymphocyte growth and development. As a result, individuals with JAK3-deficient SCID have few or no T cells and natural killer cells and a normal number of poorly functioning B cells. The shortage of functional lymphocytes causes people with this condition to be susceptible to infections.

More About This Health Condition

Other Names for This Gene

  • JAK-3
  • JAKL
  • Janus kinase 3 (a protein tyrosine kinase, leukocyte)
  • L-JAK
  • leukocyte Janus kinase
  • LJAK
  • tyrosine-protein kinase JAK3

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Catalog of Genes and Diseases from OMIM

Gene and Variant Databases


  • Notarangelo LD, Mella P, Jones A, de Saint Basile G, Savoldi G, Cranston T, Vihinen M, Schumacher RF. Mutations in severe combined immune deficiency (SCID) due to JAK3 deficiency. Hum Mutat. 2001 Oct;18(4):255-63. doi: 10.1002/humu.1188. Citation on PubMed
  • O'Shea JJ, Husa M, Li D, Hofmann SR, Watford W, Roberts JL, Buckley RH, Changelian P, Candotti F. Jak3 and the pathogenesis of severe combined immunodeficiency. Mol Immunol. 2004 Jul;41(6-7):727-37. doi: 10.1016/j.molimm.2004.04.014. Citation on PubMed
  • Pesu M, Candotti F, Husa M, Hofmann SR, Notarangelo LD, O'Shea JJ. Jak3, severe combined immunodeficiency, and a new class of immunosuppressive drugs. Immunol Rev. 2005 Feb;203:127-42. doi: 10.1111/j.0105-2896.2005.00220.x. Citation on PubMed
  • Vihinen M, Villa A, Mella P, Schumacher RF, Savoldi G, O'Shea JJ, Candotti F, Notarangelo LD. Molecular modeling of the Jak3 kinase domains and structural basis for severe combined immunodeficiency. Clin Immunol. 2000 Aug;96(2):108-18. doi: 10.1006/clim.2000.4880. Citation on PubMed

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.