ADA is involved in the development and maintenance of the immune system as it ensures the breakdown of metabolic by-products toxic to T-lymphocytes, in absence of which the toxic by-products of purine metabolism kill the T cells shortly after they are produced in the bone marrow, greatly reducing the number of T cells and resulting in ADA dependent severe acute combined immunodeficiency (SCID) (3). The gene discussed is ADA; the disease is severe combined immunodeficiency.