Adenosine deaminase deficiencyĀ (ADA deficiency) is aĀ metabolic disorderĀ that causesĀ immunodeficiency. It is caused by mutations in theĀ ADA gene. It accounts for about 10–15% of all cases ofĀ autosomalĀ recessiveĀ forms ofĀ severe combined immunodeficiencyĀ (SCID) among non-inbredĀ populations