gene therapy

The US Food and Drug Administration defines gene therapy as a technique that modifies a person's genes to treat or cure disease, seeking to modify or manipulate the expression of a gene or to alter the biological properties of living cells. That single name covers several quite different approaches.

A therapy might add a working copy of a gene that is missing or faulty, so the body can make a protein it previously could not. It might switch a gene off, or turn another one on. Or it might edit the existing sequence directly, which is what CRISPR-based treatments do. The cells being changed may be treated inside the body, or removed, altered in a laboratory and put back.

The distinction worth holding on to is between changing a gene and changing what a gene does. Both count as gene therapy, as does a one-time treatment and a repeated one. So when a story describes a gene therapy, the useful questions are which cells were changed, whether the change is expected to last a lifetime, and how long the people treated have actually been followed. That last one is usually the limit on what can honestly be claimed.