Professor Jean Manson is Head of the Neuropathogenesis Division of The Roslin Institute at the University of Edinburgh. This lecture is part of the Medical Detectives, a series of public lectures that show how keen detective work is still essential for 21st century doctors: http://www.ed.ac.uk/news/events/medical-detectives/ Recorded on 4 October 2012 in the Anatomy Lecture Theatre at the University of Edinburgh.