An unusual case of variant CJD, the human form of mad cow disease, has revived fears that some people might be infected while not yet developing symptoms.
The genetic make-up of a 30-year-old man who died from vCJD suggests some cases of infection might have incubation periods spanning decades. To date, everyone confirmed as having vCJD has had a form of the human prion protein gene known as MM. The newly identified victim, who died in January, had the MV form. Scientists led by Professor John Collinge, from the Medical Research Council Prion Unit in London, pointed out in The Lancet medical journal that related brain diseases had longer incubation periods in people with the MV prion gene. The Times, December 18, 2009