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T-B+ severe combined immunodeficiency due to gamma chain deficiency

Synonym(s) SCIDX1
T-B+ SCID due to gamma chain deficiency
T-B+ severe combined immunodeficiency, X-linked
Prevalence 1-9 / 100 000
Inheritance X-linked recessive
Age of onset Neonatal
  • D81.2
  • C2931540
MeSH -
MedDRA -


Disease definition

Severe combined immunodeficiency (SCID) due to gamma chain deficiency, also called SCID-X1, is a form of SCID (see this term) characterized by severe and recurrent infections, associated with diarrhea and failure to thrive.


It accounts for approximately 50% of SCID cases and is the most common form of SCID in Europe. The annual incidence varies among the populations but it is estimated at approximately 1/200,000 births. The disease occurs in males.

Clinical description

SCID-X1 manifests during the first months of life with severe and often life threatening viral, bacterial or fungal infections (e.g. Pneumocystis jiroveci pneumonitis, disseminated BCG infection if previously vaccinated), and failure to thrive. Chronic diarrhea is a frequent finding. Some patients may have skin rashes and abnormalities of liver function. Materno-fetal transfusion-associated graft versus host disease is also associated with the disease. Immunological findings are lymphopenia with the absence of T and NK cells, hypogammaglobulinemia, and normal or increased B cell count.


SCID-X1 results from a defect in the IL2RG gene encoding the common gamma chain.

Genetic counseling

Transmission is X-linked.

Expert reviewer(s)

  • Dr Andrew GENNERY

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Clinical genetics review
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