What is the cause of combined immunodeficiency?

Several gene defects: Combined immunodeficiency (cid) results from many gene defects, they have in common that the result is impairment of the cells of the immune system and also the production of antibodies. Cells and antibodies are essential to fight infections and also for surveillance of cancer cells.

Genetic or unknown: Many immunodeficiencies are caused by genetic mutations - i.e. Genetic defects - that may be passed from parent(s) to child. So if the mutation is known, it may be tested for. However, some immune deficiencies do not have known genetic causes. Cause may remain unknown. And, a mutation can be new - not inherited, newly developed that shows up on a test.