Large1 Gene Transfer in Older myd Mice with Severe Muscular Dystrophy Restores Muscle Function and Greatly Improves Survival

Muscular dystrophy is a progressive and ultimately lethal neuromuscular disease due to lack of therapeutic options that restore muscle function. Gene editing and gene transfer hold great promise as therapies for various neuromuscular diseases when administered prior to the onset of severe clinical symptoms. However, the efficacy of these strategies for restoring neuromuscular function and improving survival in the late stages of muscular dystrophy with severe muscle pathophysiology is unknown. Dystroglycanopathies are muscular dystrophies characterized by extensive skeletal muscle degeneration and, in many cases, are accompanied by eye and brain abnormalities. Thus far, mutations in at least eighteen human genes are known to cause dystroglycanopathies, including those in the like-acetylglucosaminyltransferase-1 ( LARGE1 ) gene. LARGE1 encodes a xylosyl- and glucuronosyltransferase that modifies α-dystroglycan (α-DG) with matriglycan, a linear repeating disaccharide of alternating xylose and glucuronic acid that binds to the laminin G-like domains of extracellular matrix proteins with high affinity. Large myd /Large myd ( myd) mice lack expression of Large1 , and exhibit severe skeletal muscle pathophysiology, impaired mobility, and a drastically reduced lifespan (50% survivorship at 35 weeks of age). Here, we show that systemic delivery of AAV2/9 CMV Large1 (AAV Large1 ) in >34-week-old myd mice with advanced disease restores matriglycan expression, attenuates skeletal muscle pathophysiology, improves motor and respiratory function, and normalizes systemic metabolism, which collectively and dramatically extends survival. Our results demonstrate that in a mouse model of muscular dystrophy, skeletal muscle function can be restored, illustrating its remarkable plasticity, and that survival can be greatly improved even after the onset of severe skeletal muscle pathophysiology.