A Phase 2 Study to Evaluate the Dose and Pharmacodynamic Efficacy of Sialic Acid-Extended Release (SA-ER) Tablets in Patients With GNE Myopathy or Hereditary Inclusion Body Myopathy

GNE myopathy or hereditary inclusion body myopathy (HIBM) is a severe progressive metabolic myopathy caused by a defect in the biosynthetic pathway for sialic acid (SA). Substrate replacement therapy is a potential therapeutic strategy based on the success of replacing missing SA and reducing muscle disease in a relevant mouse model of the human disease (Malicdan et al., 2009). Successful use of SA replacement therapy in humans is believed to depend upon providing steady long-term exposure to the compound in an extended release form (such as Sialic Acid-Extended Release \[SA-ER\]), given SA's short half-life. Following a Phase 1 study to establish the pharmacokinetics (PK) for SA-ER, Ultragenyx is conducting this study to assess the dose and potential pharmacodynamic effect of restoring sialylation of muscle by treatment with SA-ER at two dose levels as compared to placebo when administered over two 24 week periods of time. The study will also evaluate safety, as well as the effect of SA-ER on clinical measures of muscle strength, mobility, function and self-reported disability and quality of life. Effects on muscle volume/mass and function and on serum biomarkers will be evaluated as exploratory measures. These data should allow the selection of a dose and the appropriate design for a Phase 3 clinical study.