Ultragenyx Announces Positive Topline Cohort 3 Results and Improved Longer-Term Cohort 2 Results from Phase 1/2 Study of DTX301 Gene Therapy in Ornithine Transcarbamylase (OTC) Deficiency

More uniform response in Cohort 3 with two confirmed responders and one potential responder

New female responder in Cohort 2 for a total of three confirmed female responders across all cohorts

Up to six responders across all nine patients dosed in study

Prophylactic steroid cohort to begin in first half 2020; data expected in second half 2020

Ultragenyx to host conference call today at 4:30 p.m. Eastern Time

NOVATO, Calif., Jan. 09, 2020 (GLOBE NEWSWIRE) -- Ultragenyx Pharmaceutical Inc. (NASDAQ: RARE), a biopharmaceutical company focused on the development of novel products for rare and ultra-rare diseases, today announced topline positive safety and efficacy data from Cohort 3 and longer-term data from Cohort 2 of the ongoing Phase 1/2 study of DTX301, an investigational adeno-associated virus (AAV) gene therapy for the treatment of ornithine transcarbamylase (OTC) deficiency. In Cohort 3 (n=3), there were two confirmed female responders as well a third potential male responder who requires longer-term follow-up to confirm response status. In Cohort 2, one female patient has newly demonstrated a response starting at Week 52 which was confirmed at Week 78. The two previously disclosed responders in Cohort 1 and Cohort 2 also remain clinically and metabolically stable at 104 and 78 weeks, respectively. Across all nine patients dosed in the study, up to six patients have demonstrated a response.

“We are encouraged to see a more uniform response at the higher doses including three female responders. To date, three patients in the study have discontinued alternate pathway medication and liberalized their diets while remaining clinically and metabolically stable,” said Eric Crombez, M.D., Chief Medical Officer of the Ultragenyx Gene Therapy development unit. “We are moving to prophylactic steroid use in the next cohort as we believe this could further enhance the level and consistency of expression that we have demonstrated so far.”

Cohort 3 Efficacy Summary (as of December 9, 2019 cutoff date): One complete responder, one responder, and one potential responder

Patient 7 (complete responder, female):
Patient 7 demonstrated a clinically meaningful 79 percent change in rate of ureagenesis, from a low of 24 percent of normal at baseline to the 51 to 64 percent range, and staying at 44 percent of normal at Week 52. During this period, she reported feeling significantly better and discontinued her alternate pathway medications and liberalized her protein-restricted diet. She has remained clinically and metabolically stable without a rise in ammonia.