Ultragenyx Posts HIBM Topline Results

Ultragenyx Pharmaceutical has posted topline results from a 48-week Phase II 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.

Similar to the results observed at the 24-week interim analysis, at 48 weeks the comparison of the upper extremity composite of muscle strength for the combined group of patients on 6 grams showed a modest increase and a statistically significant difference relative to the decline in strength observed in the combined groups on 3 grams. In the 6-gram cohort treated for 48 weeks, the modest increase in upper extremity strength observed at 24 weeks was sustained relative to a further decline in the comparable 3-gram group. These changes were more pronounced in those patients that have less advanced disease as assessed by a greater walking ability at baseline, a predefined subset. The lower extremity composite did not show a statistically significant difference between the dose groups, but neither group showed a significant decline during the treatment period. The upper extremity and lower extremity composites are predefined endpoints that aggregate change in muscle strength across multiple individually measured muscle groups.

The data from the 48-week analysis are expected to be presented in full at a scientific conference in 2014. All 46 patients from the original study have elected to continue into the extension study. The company plans to treat patients with an increased dosage of sialic acid based on the dose-dependence observed at week 48. The first patient has already been treated with a higher dose of sialic acid, and data from the increased dose is expected in late 2014.