Discuss the use of viral vectors in gene therapy including the risks involved.

viral vector used to replace defective gene in somatic cell;
virus genetically engineered to carry normal copy of gene;
valid example; (e.g. SCID (severe combined immunodeficiency))
cause of disease; (e.g. lack of enzyme/adenosine deaminase/ADA in bone marrow cells)
technical issues need to be solved / ensure correct amount of gene product/at the right time/in the right place;
need to be sure insertion of therapeutic gene does not harm other necessary cell functions;
viral vectors may infect healthy cells;
causing illness/disease/cancer;
virus may revert to original form and cause disease;
newly introduced DNA may affect reproductive cells causing genetic changes;
immune system may attack newly introduced viruses causing inflammation/toxicity/ organ failure;

Answers failed to include enough of the range of risks needed for a high score.