Distal myopathy with rimmed vacuoles (DMRV)-hereditary inclusion body myopathy (hIBM) is an adult-onset, moderately progressive autosomal recessive myopathy; eventually, affected individuals become wheelchair bound1. It is characterized clinically by skeletal muscle atrophy and weakness, and pathologically by rimmed vacuoles, which are actually accumulations of autophagic vacuoles2, 3, 4, scattered angular fibers and intracellular accumulation of amyloid and other proteins5. To date, no therapy is available for this debilitating myopathy, primarily because the disease pathomechanism has been enigmatic. It is known that the disease gene underlying DMRV-hIBM is GNE, encoding glucosamine (UDP-N-acetyl)-2-epimerase and N-acetylmannosamine kinase6, 7, 8--two essential enzymes in sialic acid biosynthesis9. It is still unclear, however, whether decreased sialic acid production causes muscle degeneration, as GNE has been proposed to have roles other than for sialic acid biosynthesis10, 11, 12. By showing that muscle atrophy and weakness are completely prevented in a mouse model of DMRV-hIBM after treatment with sialic acid metabolites orally, we provide evidence that hyposialylation is indeed one of the key factors in the pathomechanism of DMRV-hIBM. These results support the notion that DMRV-hIBM can potentially be treated simply by giving sialic acids, a strategy that could be applied in clinical trials in the near future.