Ultragenyx Announces Progress Across Broad Gene Therapy Portfolio and Positive Longer-Term Data from Multiple Phase 1/2 Gene Therapy Studies

Durable and Clinically Meaningful Responses Reported from Phase 1/2 Studies of DTX401 for GSDIa and DTX301 for OTC

Phase 3 Studies for DTX401 and DTX301 to Begin in 2021

IND for UX701 for Wilson Disease Submitted; Expect to Enter Clinic in First Half 2021 using AAV Drug Product Made by HeLa PCL Platform

NOVATO, Calif. , Jan. 08, 2021 (GLOBE NEWSWIRE) -- Ultragenyx Pharmaceutical Inc. (NASDAQ: RARE), a biopharmaceutical company focused on the development and commercialization of novel products for rare and ultra-rare diseases, today announced positive longer-term safety and efficacy data from the first three cohorts of the ongoing Phase 1/2 studies of DTX401, an investigational adeno-associated virus (AAV) gene therapy for Glycogen Storage Disease Type Ia (GSDIa), and DTX301, an AAV gene therapy for ornithine transcarbamylase (OTC) deficiency. In addition, dosing is nearing completion for the prophylactic steroid cohorts in both studies. Discussions with regulatory agencies continue to progress for both programs, and Ultragenyx expects to initiate Phase 3 studies for DTX401 in the first half of 2021 and for DTX301 in the second half of 2021. The company also plans to start a seamless single-protocol Phase 1/2/3 study for UX701, an AAV gene therapy for Wilson disease.

“We continue to see durable and clinically meaningful responses in patients in both the DTX401 and DTX301 programs. GSDIa patients treated with DTX401 demonstrate continually improved glucose metabolism with reduction or elimination of cornstarch dependence over time. OTC patients treated with DTX301 show good metabolic control after tapering or discontinuation of alternate pathway medications and protein restricted diet,” said Eric Crombez, M.D., Chief Medical Officer of the Ultragenyx Gene Therapy development unit. “With the initiation of the UX701 program in Wilson disease and progression of DTX401 and DTX301 to Phase 3 as well as progress in our preclinical stage programs, we are leveraging our proprietary platforms to advance one of the broadest portfolios of gene therapy programs in the industry.”

DTX401 (GSDIa) Program

Phase 1/2 data update: All patients (n=9) responding and demonstrating continued improvement of glucose control while reducing or eliminating cornstarch therapy

All nine patients continue to demonstrate improved glucose control while tapering or discontinuing oral glucose replacement with cornstarch and improvements in energy metabolism pathways over the long term. Patients continue to taper the amount and frequency of cornstarch dosing with progress in eliminating overnight and daytime cornstarch doses. At the primary evaluation timepoint at Week 52, the overall mean reduction in cornstarch was 77% across all three cohorts, including two patients in Cohort 3 showing a reduction of greater than 75%. Longer term follow-up for more than two years for the three patients in Cohort 1 have shown sustained and continued cornstarch reductions with a mean reduction of 91% through weeks 104 and 120. Two patients (one each from Cohort 1 and 3) are completely off cornstarch therapy at weeks 127 and 60, respectively.