What is gene therapy, in simple terms?

Our genes are instructions for building the proteins that keep our bodies running. When a gene has a harmful change, the protein it makes may not work, and disease can follow. Gene therapy tries to fix the problem at its source rather than managing symptoms.

The most common approach is gene replacement: scientists package a healthy copy of the gene into a delivery vehicle, called a vector, and give it to the patient. The vector carries the new gene into cells, which can then use it to make the working protein. The U.S. Food and Drug Administration has approved several gene therapies for other rare genetic conditions.

In nonketotic hyperglycinemia, the broken genes build the glycine cleavage system that clears glycine. The idea behind the therapy the O'Sullivans are pursuing is to deliver a working copy so cells can begin clearing glycine themselves.

Gene therapy is powerful, but it is still medicine with risks and unknowns, and each new therapy must be tested carefully in clinical trials. Read about EmetAbba, the therapy planned for Drake and Vivian's trial, or see what it can and can't promise.

Sources: U.S. FDA: What is Gene Therapy? · MedlinePlus Genetics: What is gene therapy?