Gene Therapy

The first clinical gene therapy was given in 1990 to a 4-year-old girl suffering from adenosine deaminase (ADA) deficiency.
ADA is an enzyme essential for the functioning of the immune system; the disorder is caused by deletion of the ADA gene.
Lymphocytes from the patient's blood were grown in culture, a functional ADA cDNA was introduced into them using a retroviral vector, and the cells were returned to the patient.
Diabetes mellitus is treated with insulin, chicken pox is a viral infection and rheumatoid arthritis is an auto-immune disorder; none of them was the first target of gene therapy.
Hence the first clinical gene therapy was for adenosine deaminase deficiency.

ADA deficiency is caused by the deletion of the gene for adenosine deaminase, an enzyme crucial for the immune system to function.
Enzyme replacement therapy (injecting functional ADA) and bone marrow transplantation are not completely curative.
In gene therapy, lymphocytes from the patient's blood are grown in culture, a functional ADA cDNA is introduced into them using a retroviral vector, and they are returned to the patient. Since these cells are not immortal, the patient requires periodic infusion of such lymphocytes; so this is not a permanent cure either.
However, if the gene isolated from marrow cells producing ADA is introduced into cells at early embryonic stages, it could be a permanent cure.
Hence the permanent cure is introducing bone marrow cells producing ADA into cells at early embryonic stages.