What causes SCID?

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. It is caused by a mistake (or mutation) in a child’s genetic make-up. Specialists in genetics and genetic counselling are on hand to talk through the inheritance of SCID with you if needed, and PID UK has a separate information leaflet devoted to the genetics of primary immunodeficiency. 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. Recent developments in genetics mean that doctors are now often able to make a specific SCID diagnosis. The names given to the different types of SCID are based on the particular protein or gene that is affected. 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. 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.

Reviewed April 2017