Severe combined immunodeficiency

The information in this section of the website is designed to help answer the questions families may have about the immune condition called severe combined immunodeficiency (SCID). The content has been produced jointly between Immunodeficiency UK, Great Ormond Street Hospital (GOSH) and the Great North Children’s Hospital and has been reviewed by the Immunodeficiency UK Medical Advisory Panel and Patient Representative Panel and by families affected by SCID.

Specific information on X-linked SCID and ADA-SCID is available but we recommend that this information is read in conjunction with this overview of SCID.


SCID is the name given to a group of rare, inherited disorders that cause major abnormalities of the immune system. They form part of a larger group of conditions known as primary immunodeficiencies. The immune system abnormalities in SCID lead to greatly increased risks of infection and other complications that are life-threatening. Affected infants become unwell within the first few months of life, and before modern medication and treatments were available, most affected babies did not survive beyond their first year. Today, doctors understand much more about SCID. Treatment is now available that can reduce the risk of serious infection, and in many cases, cure the disorder.

There are many different types of SCID, each with different genetic causes. However, infants affected by the various types of SCID have many features in common and these are described here. In all infants affected by SCID, specialised white blood cells, known as lymphocytes, are missing or not functioning properly. The three main types of lymphocytes that can be affected are called T-cells, B-cells and natural killer (‘NK’) cells.

Continuing developments and improvements are transforming the lives of children with SCID. Advances in diagnostic techniques and genetic technology, improved treatments and better medications enable many children with SCID to proceed through stem cell transplant safely. It is likely that gene therapy will continue to develop and become applicable to more types of SCID.

Reviewed April 2017