The backlash surrounding aducanumab post-approval has put Biogen (NSDQ:BIIB) on the defensive, prompting the company’s head of research and development, Dr. Alfred Sandrock, to post an open letter to the Alzheimer’s disease community on Biogen’s website. In the letter, Sandrock lamented that there was “extensive misinformation and misunderstanding” regarding the drug. In recent weeks, the company also requested…