Answer
Adenosine deaminase enzyme is very important for functioning of immune system. ADA deficiency is due to delection of the gene for adenosine deaminase.
Possible permanent cure is gene therapy where lymphocytes from the blood of the patients are grown in a culture outside the body. Then functional ADA is introduced into these lymphocytes which are then introduced into patient.
However it is important that gene isolated from marrow cells producing ADA is introduced
into cells at early embryonic stage for permanent cure.