SGSH and Abnormal retinal morphology: To enable a head‐to‐head comparison of the two clinically relevant routes of delivery of AAV9‐sulfamidase, we performed intra‐CSF infusions of vector into the lateral ventricles of neonatal MPS IIIA mice and the impact on retinal disease at 20 weeks of age was compared to that observed following i.v. delivery of the same vector at the same disease stage.