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Upper extremity muscle strength composite shows statistically significant difference between the 6 gram and 3 gram dose groups

Novato, CA — December 20, 2013 — Ultragenyx Pharmaceutical Inc., a biopharmaceutical company focused on the development of novel products for rare and ultra-rare diseases, today announced topline results from a 48-week Phase 2 clinical study of sialic acid extended-release (SA-ER, UX001) tablets in 46 patients with hereditary inclusion body myopathy (HIBM), a progressive muscle-wasting disease. SA-ER is designed to replace the deficient sialic acid substrate in patients with HIBM. Patients were initially randomized to either receive placebo, 3 grams or 6 grams of SA-ER per day. After 24 weeks, placebo patients crossed over to either 3 grams or 6 grams total daily dose, on a blinded basis, for an additional 24 weeks. The final analysis compared change at week 48 from baseline for the combined groups at 6 grams versus 3 grams of SA-ER.