a treatment where a defective gene is replaced by a corrected gene. Often this is done by transporting the corrected gene into the body on a viral vector that is genetically modified to be non-infective and incapable of replication. This virus will enter cells and deliver the corrected copy of the gene to the nucleus, resulting in production of the missing or non-mutated protein.. There are scientists who specialize in creating the right vectors for carrying genes to specific places in the body.