Viral vector-mediated SLC9A6 gene replacement reduces cerebellar dysfunction in the shaker rat model of Christianson syndrome

Christianson syndrome (CS) is an x-linked recessive neurodevelopmental and neurodegenerative condition characterized by severe intellectual disability, cerebellar degeneration, ataxia, and epilepsy. Mutations to the SLC9A6 gene are responsible for CS, and we recently demonstrated that a mutation to the rat Slc9a6 gene causes a similar phenotype in the spontaneous shaker rat model, which exhibits cerebellar degeneration with motor dysfunction. In previous work, we used the PhP.eB-L7-Slc9a6-GFP adeno-associated viral (AAV) vector to demonstrate that gene replacement in Purkinje cells reduced the shaker motor and molecular phenotype. Here, we carried out a 20-week longitudinal study evaluating the impact of Purkinje cell-specific gene replacement on ataxia and tremor. Taking advantage of the high homology between human SLC9A6 and rat Slc9a6 , we tested a more clinically relevant construct, AAV9-CAG-hSLC9A6 AAV vector in the shaker rat. Administration of either of PhP.eB-L7-Slc9a6-GFP or AAV9-CAG-hSLC9A6 AAV vectors led to significant improvement in the molecular and motor phenotypes. The abundance of several disease-relevant cerebellar proteins was significantly correlated to motor performance. Finally, we found evidence that tremor and ataxia phenotypes in may arise from dissociable cerebellar mechanisms in the context of CS. These findings impact future SLC9A6 -targeted gene therapy efforts for CS and strongly support gene replacement as a viable therapeutic strategy.