Adenosine deaminase deficiency (ADA)
is an inherited condition that affects the immune system and typically leads to severe combined immunodeficiency (SCID). People with SCID have a reduced or absent immune response which leaves them vulnerable to frequent bacterial, viral, and fungal infections. Most people affected by ADA develop symptoms of the condition before 6 months of age. However, approximately 10-15% of affected people have a "delayed" onset of symptoms; diagnosis of these cases, which are often less severe, typically takes place later in childhood (often between age 1 and 10) or even into adulthood. Signs and symptoms of ADA include pneumonia, chronic diarrhea, widespread skin rashes, slowed growth and/or developmental delay. ADA is caused by changes (mutations) in the ADA gene and is inherited in an autosomal recessive manner. The most effective treatment is transplantation of blood-forming stem cells from the bone marrow of a healthy person. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.