Severe Combined Immunodeficiency (SCID)

SCID is a group of rare disorders caused by mutations in different genes involved in the development and function of infection-fighting T, B, and natural killer cells. Infants with SCID appear healthy at birth but are highly susceptible to severe infections. The condition is fatal, usually within the first year or two of life, unless infants receive immune-restoring treatments, such as transplants of blood-forming stem cells, gene therapy, or enzyme therapy. More than 80 percent of SCID infants do not have a family history of the condition. However, development of a newborn screening test has made it possible to detect SCID before symptoms appear, helping ensure that affected infants receive life-saving treatments.

Why Is the Study of Severe Combined Immunodeficiency (SCID) a Priority for NIAID?

SCID is a group of rare genetic disorders that may be chronic, debilitating, and costly. By learning more about these disorders and their effects on the body, scientists gain a greater understanding of immune function that can inform multiple areas of research.

How Is NIAID Addressing This Critical Topic?

Research supported by NIAID and other organizations has shown that early diagnosis of SCID through newborn screening leads to prompt treatment and high survival rates. Early transplantation is critical to achieving the best outcomes for SCID infants. Researchers at NIAID and NIAID-supported institutions also have shown that gene therapy can be an effective treatment for some types of SCID, such as X-linked SCID.

SCID is a primary immune deficiency disease (PIDD). For more information on PIDD research and patient care at NIAID, visit the NIAID PIDD site

Photo of blood being collected from a newborn for screening.
Credit: U.S. Air Force

Blood is collected from a newborn for screening.


SCID is caused by defects in different genes involved in the development and function of infection-fighting immune cells. More than a dozen genes have been implicated in SCID, but gene defects are unknown in approximately 15 percent of newborn-screened SCID infants.

Symptoms & Diagnosis

Typically, symptoms of SCID occur in infancy and include serious or life-threatening infections, especially viral infections, which result in pneumonia and chronic diarrhea. Candida (yeast) infections of the mouth and diaper area and pneumonia caused by the fungus Pneumocystis jirovecii also are common in affected infants.


Hematopoietic (blood-forming) stem cell transplantation is the standard treatment for infants with SCID. Ideally, SCID infants receive stem cells from a sibling who is a close tissue match. 

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Content last reviewed on June 24, 2016