An example of how difficult it is to conclude that gene therapy is effective is the case of the life-threatening disorder known as SCID – Severe Combined Immunodeficiency Disorder – in which sufferers have little or no functioning immune system.
It happens when the T-lymphocytes in the blood, which normally direct the rest of the immune system to respond to any foreign invader in the body, do not function properly. If the disorder is detected soon enough after a baby has been born, they can be placed in a protective, germ-free “bubble”.
Obviously this isolation from normal life is not ideal for the child or the family. Bone marrow transplants have helped these babies, but this relies on finding suitable donors, and may have to be repeated several times, and sometimes are only partially successful or do not work at all.
Trials conducted since 1990 to try to treat children with SCID by gene therapy have had some successes. In 2000 it was reported that two children who had received no prior treatment by bone marrow transplant, appeared to be developing normally in good health with no other treatment following their gene therapy.
But in late 2003 a worrying report in the journal Science was published that showed that, following gene therapy another two young boys had developed a leukaemia-type disease. Scientists discovered that the corrected DNA inserted to replace the defective cells had been placed next to a gene that was a known inhibitor of leukaemia.
USEFUL WEB LINKS:
You can read more about SCID on SCID.NET or the Nemours Foundation's Kids Health pages.