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JAK3-deficient severe combined immunodeficiency
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

JAK3-deficient severe combined immunodeficiency

JAK3-deficient severe combined immunodeficiency (SCID) is an inherited immune system disorder that leaves individuals highly susceptible to life-threatening infections.

Overview

JAK3-deficient severe combined immunodeficiency (SCID) is an inherited disorder where the body lacks the necessary immune cells to fight bacteria, viruses, and fungi. Affected infants are prone to persistent, serious infections and often develop chronic diarrhea, oral thrush, pneumonia, and skin rashes. Due to persistent illness, affected children grow more slowly than their peers. Without treatment, the condition is typically fatal in early childhood.

Causes

The condition is caused by mutations in the JAK3 gene. The JAK3 protein is critical for the growth and maturation of lymphocytes, specifically T cells and natural killer cells, and is also important for the maturation of B cells. Mutations prevent the production of functional JAK3 protein, leading to an absence of T cells and natural killer cells and a population of poorly functioning B cells. This shortage of functional lymphocytes leaves the immune system unable to defend the body.

Inheritance

This condition is inherited in an autosomal recessive pattern. This means that both copies of the JAK3 gene in each cell must have mutations for the condition to occur. Parents of an affected individual each carry one copy of the mutated gene but typically do not exhibit signs or symptoms of the disorder.

Frequently Asked Questions

Look for persistent thrush, chronic diarrhea, failure to thrive, recurrent or unusual infections (viral, bacterial, fungal) and a lack of response to standard antibiotics. A complete blood count often shows very low lymphocyte counts, prompting further immunologic work‑up.
Diagnosis relies on flow cytometry showing absent or markedly reduced CD3⁺ T cells and NK cells, with low‑functional B cells. Genetic sequencing of the JAK3 gene identifies pathogenic mutations. Additional tests include T‑cell receptor excision circles (TRECs) and functional assays of cytokine signaling.
Carrier testing confirms each parent’s status. Options include pre‑implantation genetic diagnosis (PGD) with IVF to select embryos without the mutation, prenatal chorionic villus or amniocentesis testing, or use of donor gametes. Genetic counseling is strongly recommended.===
The standard curative option is hematopoietic stem cell transplantation (HSCT) from a matched sibling or unrelated donor, with survival rates >80 % when performed early (<3‑4 months of age). Emerging gene‑therapy trials using autologous stem cells corrected with a functional JAK3 transgene show promising immune reconstitution, but are still investigational.
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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