Ultragenyx (RARE) Begins Dosing in Phase I/II Study of UX053 Posted byZacks Equity Research December 2, 2021 Leave a comment on Ultragenyx (RARE) Begins Dosing in Phase I/II Study of UX053 Ultragenyx (RARE) doses the first patient in a phase I/II study evaluating its investigational mRNA candidate, UX053, for treating glycogen storage disease type III.