To determine whether the amelioration of CNS pathology in MPS-IIIA mice that were injected with AAVs encoding the fully modified sulphamidase resulted in an improvement in the behavioural phenotype, we monitored the exploratory activity in control normal mice, control MPS-IIIA mice, and MPS-IIIA mice treated with fully modified sulphamidase. The gene discussed is SGSH; the disease is mucopolysaccharidosis.