AAV-Mediated Gene Delivery Corrects CNS Lysosomal Storage in Cats with Juvenile Sandhoff Disease

Sandhoff Disease (SD) is an autosomal recessive neurodegenerative disease caused by a mutation in the Hexb gene for the β-subunit of β-hexosaminidase A, resulting in the inability to catabolize ganglioside GM2 within the lysosomes. SD presents with an accumulation of GM2 and its asialo derivative GA2 primarily in the CNS. Myelin-enriched glycolipids, cerebrosides and sulfatides, are also decreased in SD corresponding with dysmyelination. At present, no treatment exists for SD. Previous studies have shown the therapeutic benefit of using adeno-associated virus (AAV) vector-mediated gene therapy in the treatment of SD in murine and feline models. In this study, CNS tissue was evaluated from SD cats (4-6 week old) treated with bilateral injections of AAVrh8 expressing feline β-hexosaminidase α and β into the thalamus and deep cerebellar nuclei (Thal/DCN) or into the thalamus combined with intracerebroventricular injections (Thal/ICV). Both groups of treated animals had previously shown improved quality of life and absence of whole-body tremors. The activity of β-hexosaminidase was significantly elevated whereas the content of GM2 and GA2 was significantly decreased in tissue samples taken from the cerebral cortex, cerebellum, thalamus, and cervical intumescence. Treatment also increased levels of myelin-enriched cerebrosides and sulfatides in the cortex and thalamus. This study demonstrates the therapeutic benefits of AAV treatment for feline SD and suggests a similar potential for human SD patients.