A California health official says two cases of what appears to be Creutzfeldt-Jakob disease in Marin County could be coincidence.
One of the victims has died, the Marin Independent Journal reported.
Dr. Craig Lindquist, the county public health officer, said the doctors treating the two patients reported the diagnosis to the state, which alerted him last week.
"There is no information suggesting a causal link between the two cases; nor is there any information that suggests a risk to the public," he said.
A variant form of Creutzfeldt-Jakob occurs from eating beef from cattle with bovine spongiform encephalopathy, known as mad cow disease. BSE is caused by protein fragments known as prions.
The more common form of Creutzfeldt-Jakob, although it is also rare, is caused by genetic mutation or by the introduction of contaminants during medical procedures. Both forms cause brain deterioration leading to dementia and death.
Craig McAllister of Oakland told the Independent Journal the dead patient might be his ex-wife, Aline Shaw of San Rafael. He said they lived in London from 1989 to 1992 at a time when there was an outbreak of BSE among British cattle.
Researchers are unsure how long people with Creutzfeldt-Jakob remain without symptoms although they suspect it may be decades in some cases.