It has been thought that there might be a genetic link between Alzheimer’s disease and Parkinson’s disease, but that seems not to be the case.

Researchers have found that the odds of developing Alzheimer’s disease is not increased among relatives of people who have Parkinson’s disease, compared with relatives of unaffected “control” subjects.

It seems unlikely therefore that there are “major shared genetic contributions” to the development of these two diseases, according to a report in the July issue of the Archives of Neurology.

Dr. Karen Marder from Columbia University, New York, and associates determined the disease status of first-degree relatives of 487 people with Parkinson’s disease without dementia and 409 matched subjects without Parkinson’s disease, using a structured family history interviews.

All told, the study included 4819 relatives of Parkinson’s patients, and 2285 relatives of control participants.

A diagnosis of Alzheimer’s disease was reported for 61 relatives of people with Parkinson’s disease, and 52 relatives of controls. That worked out to almost exactly the same percentage in each group - 2.3 percent and 2.4 percent.

“If there were a major shared genetic influence on Parkinson’s disease and Alzheimer’s disease, we would have expected both an increased risk of Parkinson’s disease in Alzheimer’s disease families and an increased risk of Alzheimer’s disease in Parkinson’s disease families,” Marder told Reuters Health.

“While clearly there is some overlap in some families in which Alzheimer’s disease and Parkinson’s disease co-exist, there is probably not a huge overlap,” Marder concluded.

SOURCE: Archives of Neurology, July 2004.