Final answer:
Gene therapy is the use of genetic engineering to treat or prevent diseases by replacing or correcting defective genes with functional ones, often using viral vectors.
Step-by-step explanation:
The use of genes to treat or prevent disease is called gene therapy. This genetic engineering technique involves the introduction of a non-mutated gene into the genome to replace a defective protein caused by a mutated gene. The new gene, typically introduced into diseased cells through a vector like a virus, can integrate with the host cell's DNA and produce functional proteins to combat the disease. Advanced forms of gene therapy aim to correct the mutation at the original site in the genome. Conditions such as severe combined immunodeficiency (SCID) have been treated using gene therapy, and while it remains an experimental approach, it has seen successes and holds promise for future medical treatments.