AAV-mediated gene therapy demonstrates phenotypic rescue in a mouse model of Cockayne syndrome

Cockayne syndrome (CS) is an autosomal recessive, progressive developmental and neurodegenerative disease. Approximately 30% of cases are caused by mutations in the ERCC8/CSA gene. Patients with CS present with cutaneous photosensitivity, growth failure, shorter life span, and a progressive degeneration of the central nervous system. Loss-of-function mutations in CSA result in deficiencies in transcription-coupled nucleotide excision repair. Currently, no therapies are available for these patients. Adeno-associated virus-mediated (AAV-mediated) gene therapy offers an opportunity to address this unmet need. We designed an AAV vector encoding human CSA under a ubiquitous promoter. We tested the therapeutic efficacy of this AAV9-CSA vector by neonatal intracerebroventricular injection in the Csa-/- Xpa-/- mouse model. Treatment with AAV9-CSA resulted in a significant increase in life span, and broad distribution of human CSA in the brain and heart, without evidence of vector-related toxicity. Despite clear therapeutic benefit, we also observed neuroradiological abnormalities, and neuropathologic alterations, including hypomyelination, astrocytosis, and microgliosis, as well as likely life-limiting transcriptomic alterations in liver at endpoint. Nonetheless, the success of these experiments paves the way for clinical translation of an AAV gene therapy for patients with CS into humans.