The ADA gene (ADA stands for "adenosine deaminase") is a protein-coding gene located on chromosome 20q13.12. The ADA gene encodes the enzyme "adenosine deaminase", which catalyzes the hydrolysis of adenosine to inosine in the purine catabolism pathway.
Several mutations have been described for this gene that are associated with human diseases related to impaired immune function, such as severe combined immunodeficiency disease (SCID), which is due to a deficiency of the ADA enzyme.
In individuals with ADA deficiency, there is a marked reduction in T, B, and NK lymphocytes. This leads to a deficiency in humoral and cellular immunity.