Lafora disease gene therapy: EPM2A but not EPM2B overexpression results in Lafora body formation

Lafora disease (LD) is a fatal teenage-onset neurodegenerative epilepsy caused by loss-of-function mutations of the genes encoding the laforin phosphatase-malin E3 ubiquitin ligase complex. This complex regulates glycogen structural integrity, through yet unclear mechanisms. Deficiencies of the complex lead few glycogen molecules at a time to misshape, precipitate and cumulate into toxic Lafora bodies (LBs) that drive LD. We developed an intrathecal AAV9-based gene therapy for malin-deficient LD and obtained preclinical efficacy without toxicity. A similar gene therapy for laforin-deficient LD also afforded efficacy, but with a relatively narrow therapeutic window. When overexpressed, laforin paradoxically led to LB generation and did so at a rate higher than in LD. The phenomenon was invariably observed first and dominantly in dorsal root ganglia (DRG) and occurred irrespective of where in the CSF axis the viral vector was delivered. Laforin overexpression-mediated LB formation represents novel biology, which we characterize and show that it occurs independently of laforin and malin's enzymatic activities. The accumulations are time-dependent, which toward clinical development will necessitate longer preclinical and clinical safety monitoring. The effect is strongest with species mismatch (i.e., expression of human laforin in mice), which may require matched-species preclinical development. Finally, the DRG are sentinel, and their pathology and neurophysiology can serve to monitor the iatrogenic toxicity. Our work suggests a clear gene therapy development path for malin-deficient LD, and sets important guardrails for gene therapy for laforin-dependent LD. It also opens a new avenue to understanding the basic biologies of glycogen quality control and LD.