AAV (Adeno-Associated Virus)

**What it means:** AAV is a tiny, harmless virus used as a **delivery vehicle** (vector) to carry therapeutic genes into cells. Think of it like a Trojan horse — the virus looks normal from the outside (it won't cause disease because it's been stripped of everything harmful), but inside it's carrying a healthy copy of the MEF2C gene as cargo. **Why AAV specifically?** AAV is the "gold standard" gene therapy vector because it: - Doesn't cause disease in humans (it's very safe) - Can infect both dividing and non-dividing cells (important for neurons, which don't divide) - Stays in the cell long-term without integrating into the host genome (reduces safety risks) - Has been used in seven FDA-approved gene therapies already (Luxturna, Zolgensma, etc.) **The limitation:** AAV has a small cargo capacity — it can only carry relatively small genes. This is why the MEF2C gene had to be carefully optimized to fit inside the AAV vector. If MEF2C were any larger, it wouldn't fit.