The disease incubates up to 30 years, and victims survive less than a year after the onset of symptoms. Patients typically show profound mental deterioration, muscle spasms, tremor and loss of coordination. The iatrogenic infections incubate 15 months to 30 years. After onset at a mean age of 60, the disease usually lasts between seven and nine months. Worldwide, one out of every million people is affected.
Patients show lack of coordination and difficulty walking.
Dementia is comparatively minor, though some families show a more profound manifestation. The disease lasts for five years on average, with onset at midlife. In the past, it has been mistaken as familial Alzheimer's disease, particularly since spongiform changes of the brain may be absent. It's extremely rare and was only recently discovered. It strikes in middle or late life, with an average duration of 13 months.