How can gene therapy restore function in a genetic disease? Example.

• A. It uses gene editing to delete the defective gene
• B. It introduces a correct copy of the gene into patient cells using viral or non-viral vectors
• C. It blocks all gene expression in affected tissues
• D. It replaces the entire genome of the patient

Answer: (B)

Delivering a functioning copy of the gene into patient cells so they can make the missing or defective protein is how gene therapy can restore the lost function. By introducing this healthy gene using vectors—viral vectors that carry the gene or non-viral delivery systems—the cells start producing the correct protein again, which can reestablish the normal cellular activity and tissue function that the mutation disrupted. The delivered gene may persist as an extra copy or integrate into the genome, depending on the method, but the goal is the same: restore protein production and function.

Other ideas wouldn’t achieve restoration of function in the same way. Deleting the defective gene removes its product entirely rather than supplying a working version. Blocking all gene expression would suppress activity rather than fix the underlying deficit. Replacing the entire genome isn’t a practical therapeutic approach with current technology and would go far beyond how gene therapy is designed to work.