1. Sean M. Healey & AMG Center for ALS, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
2. Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
3. Biogen, Cambridge, MA, USA
4. Department of Physical Medicine and Rehabilitation, Spaulding Rehabilitation Hospital, Harvard Medical School, Boston, MA, USA and
5. Massachusetts General Hospital, Biostatistics Center, Harvard Medical School, Boston, MA, USA