Avidity Biosciences (RNA) investor relations material

Study design and participant characteristics

• EXPLORE44 was a randomized, double-blind, placebo-controlled trial in boys and young men with DMD amenable to exon 44 skipping, followed by an open-label extension (OLE) where all received del-zota at 5 mg/kg every six weeks.

• The OLE included 39 participants aged 7–27, both ambulatory and non-ambulatory, with most on corticosteroids; 67% were ambulatory and 90% on steroids.

• Functional data are from participants with at least one year of continuous del-zota treatment.

• 26 participants were enrolled in the initial trial, with 23 rollover and 16 direct enrollees in the OLE.

Efficacy and biomarker results

• Del-zota treatment led to dystrophin increases up to 58% of normal, with robust improvement from baseline; near full-length dystrophin reached >30% of normal in some, approaching levels seen in asymptomatic carriers.

• Creatine kinase levels were rapidly reduced by over 80% and maintained near normal for up to 16 months; 50% of participants had normal CK at one year.

• Statistically significant and clinically meaningful improvements were observed in 4-stair climb, 10m walk/run, time to rise from floor, NSAA, and upper limb function at one year, with del-zota-treated patients showing gains while natural history controls declined.

• Functional improvements included a 2.1 second gain in 4-stair climb, 0.7 second gain in 10-meter walk/run, 3.2 second gain in time to rise from floor, and 1.5 point gain in upper limb function, while natural history groups declined.

• Improvements exceeded clinically meaningful differences for all major endpoints and were consistent across ambulatory and non-ambulatory patients.

Safety and tolerability

• Most adverse events were mild or moderate; 26% were related to study drug, and 8% were serious adverse events.

• One serious adverse event (moderate hypersensitivity) was related to treatment and led to discontinuation; no deaths occurred.

• Most common adverse events included upper respiratory symptoms, diarrhea, falls, back pain, and headache.

• No new safety signals emerged, and the safety profile remains favorable over long-term follow-up.