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JAK3 gene

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

JAK3 gene

The JAK3 gene provides instructions for a protein critical to the development and function of the immune system.

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 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:

  • T cells
  • Natural killer cells
  • B cells

These lymphocytes are essential for attacking bacteria, viruses, and fungi and regulating the 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, life-threatening infections.

Most mutations in the JAK3 gene prevent the production of the JAK3 protein or result in a protein that is unstable and quickly broken down. Without functional JAK3 protein, chemical signals are not relayed to the nucleus, impairing lymphocyte growth. As a result, individuals with this condition have:

  • Few or no T cells
  • Few or no natural killer cells
  • A normal number of poorly functioning B cells

Other Names for This Gene

  • JAK-3
  • JAK3_HUMAN
  • JAKL
  • Janus kinase 3 (a protein tyrosine kinase, leukocyte)
  • L-JAK
  • leukocyte Janus kinase
  • LJAK
  • tyrosine-protein kinase JAK3

Frequently Asked Questions

Place the infant in a protective isolation environment (e.g., a HEPA‑filtered room), avoid live vaccines, restrict visitors, and start prophylactic antibiotics/antifungals as directed by the immunology team. Early referral for definitive therapy such as hematopoietic stem‑cell transplantation (HSCT) or gene‑editing therapy is essential, ideally within the first few months of life.
Yes. JAK3‑related SCID follows an autosomal‑recessive inheritance pattern, so each sibling has a 25 % chance of being affected, a 50 % chance of being a carrier, and a 25 % chance of being unaffected and not a carrier. Carrier testing is done by targeted DNA sequencing of the known family mutation, usually through a clinical genetics laboratory.
The optimal donor is a human leukocyte antigen (HLA)‑matched sibling, because it offers the lowest risk of graft‑versus‑host disease and higher engraftment rates. If no matched sibling is available, a matched unrelated donor (MUD) or a haploidentical parent donor with post‑transplant cyclophosphamide can be considered. The transplant team will evaluate donor availability, HLA compatibility, and the child’s overall health before deciding.
Yes. Recent clinical trials have used autologous hematopoietic stem cells that are genetically corrected with a functional JAK3 cDNA using a lentiviral vector. Early results show successful immune reconstitution and reduced infection rates, but the therapy is still investigational and typically available only at specialized centers.
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.