Effect of disease progression on CSF-directed AAV gene therapy in a large brain animal model of lysosomal storage disease

The lysosomal storage disease alpha-mannosidosis (AMD) is caused by a genetic deficiency of lysosomal alpha-mannosidase, leading to the widespread presence of storage lesions in the brain and other tissues. Animal models of lysosomal diseases have demonstrated the benefit of early treatment; however, many human diagnoses occur after patients are symptomatic. We demonstrate here partial correction of the globally distributed storage lesions by infusion of a high dose of adeno-associated virus 1-feline alpha-mannosidase into the cerebrospinal fluid via the cisterna magna in the gyrencephalic AMD cat brain at different ages, corresponding with different stages of disease progression. Significant improvements in clinical parameters were observed, and partial correction was documented <i>pre mortem</i> by non-invasive magnetic resonance spectroscopy and diffusion tensor imaging. <i>Post mortem</i> analysis demonstrated that higher levels of lysosomal alpha-mannosidase activity in animals treated at 12 weeks of age did not translate into increased correction of lysosomal storage lesions throughout the brain when compared with animals treated at earlier time points. These results further demonstrate the importance of early detection and treatment of a lysosomal storage disease to successful outcomes.