Final answer:
The first gene therapy trial aimed to replace the ADA enzyme to treat SCID, a genetic disease with a specific single gene defect, making it a suitable candidate for such interventions. While successful, the therapy required ongoing treatments, showing promise for SCID patients, particularly when bone marrow transplants are not viable.
Step-by-step explanation:
In the first gene therapy trial designed to cure or partially cure a patient, there was an attempt made to replace the adenosine deaminase (ADA) enzyme. ADA deficiency is one type of severe combined immunodeficiency (SCID), a genetic disorder where the lack of ADA leads to a buildup of toxins that destroy immune cells, compromising the immune system and preventing it from fighting infections. Bone marrow cells were taken from a SCID patient, the ADA gene was inserted into these cells, and then the modified cells were put back into the patient's bloodstream. While the treatment was successful in restoring immune function, it required repeated treatments to maintain efficacy.
SCID is a good disease for early attempts at gene therapy because it's caused by a single gene defect, making it easier to correct with gene therapy than diseases with more complex genetic causes. Additionally, new treatments for SCID do not require the tissue match that is necessary for standard bone marrow transplants, offering a significant advantage, especially for those in whom bone marrow transplantation has failed.