A hereditary condition is adenosine deaminase deficiency. A person has an ADA deficiency if there is a reduced level of ADA in their blood. Treatment options for this condition include ADA enzyme in a enzyme replacement therapy and bone marrow transplantation. The method of treating ADA is not completely curative. The patient receives an ADA injection as a part of enzyme replacement treatment. Introduction of genes that make ADA from bone marrow cells into the patient's cells at a very early stage of embryogenesis. With the use of gene therapy, it can be permanently cured.