Although the management and treatment of infants with SCID is usually very similar for all types, it is important to know the exact cause: (a) because in some conditions there may be specific treatments available, and (b) to allow accurate genetic counselling for future pregnancies. Some of the more frequently encountered types include common gamma chain deficiency, adenosine deaminase (ADA) deficiency, JAK 3 kinase deficiency, MHC class II deficiency, and recombinase activating gene (RAG) deficiency. The names given to the different types of SCID are based on the particular protein or gene that is affected. Recent developments in genetics mean that doctors are now often able to make a specific SCID diagnosis. In infants affected by SCID, a genetic mistake results in the absence or malfunction of a protein that is necessary for normal development and/or function of the immune system. Many different genes can be affected, each causing a different type of SCID.

Specialists in genetics and genetic counselling are on hand to talk through the inheritance of SCID with families if needed, and we have a separate information leaflet devoted to the genetics of primary immunodeficiency available on our website.

It is caused by a mistake (or mutation) in a child’s genetic make-up. SCID is an inherited condition, meaning it is passed on in families in the same way as physical characteristics, such as eye colour, are passed from parent to child. The three main types of lymphocytes that can be affected are called T-cells, B-cells and natural killer (‘NK’) cells. In all infants affected by SCID, specialised white blood cells, known as lymphocytes, are missing or not functioning properly. 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 in this leaflet. Treatment is now available that can reduce the risk of serious infection, and in many cases, cure the disorder. Today, doctors understand much more about SCID. 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. 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. Severe combined immunodeficiency (SCID) is the name given to a group of rare, inherited disorders that cause major abnormalities of the immune system.

What is scid caused by