Biogen loses head of R&D, the latest blow to the struggling drugmaker

Biogen is facing what many say is a critical year for its business, with its portions of its drug pipeline crumbling and new competition closing in. Now, the drugmaker is going to have to address those dilemmas without one of its scientific experts.

Michael Ehlers is leaving the Cambridge drug giant to become the CEO of a new gene therapy-focused startup, Limelight Bio.