** Shares of drug developer Regenxbio RGNX.O fall 18.7% to $8.16 premarket

** Co says its experimental gene therapy for duchenne muscular dystrophy met the main goal of a late-stage study

** Co says 93% of participants reached at least 10% microdystrophin expression, the muscle-protecting protein missing or defective in people with Duchenne, at 12 weeks

** The trial evaluated RGX-202 in 31 ambulatory boys aged 1 year and older; two serious adverse events were reported, both were easily managed and resolved within weeks, co says

**"Two serious adverse events muddy the update and FDA feedback will be debated as we await additional clarity from RGNX’s upcoming meeting with FDA prior to BLA filing" - Leerink Partners

** Duchenne muscular dystrophy is a rare neuromuscular disease characterized by worsening muscle weakness and loss of function

** Co plans to discuss this data with the FDA at a future meeting and pursue accelerated approval for RGX-202

** Up to last close, stock down 30.3% YTD