** Shares of drug developer PepGen PEPG.O fall 17% to $5.60 in extended trading
** PEPG says the U.S. FDA has put a partial clinical hold on its mid‑stage trial of a rare muscle disease drug
** The drug, PGN‑EDODM1, is being tested for myotonic dystrophy type 1, which causes progressive muscle weakness
** Co says the health regulator's concerns relate to earlier lab and animal studies the company submitted
** PEPG says it's working with the FDA to address the questions and will submit additional info
** PEPG rose 72.7% in 2025
(Reporting by Kamal Choudhury in Bengaluru)
((Kamal.Choudhury@thomsonreuters.com;))