That makes genetic studies more efficient, because scientists have to sift through fewer chunks of DNA. Because founder populations were established by only a few people, these groups have higher levels of genetic homogeneity. That means there are fewer causes for each disease, which makes it easier to find specific causes, says Reich.
This is the case in the recent Parkinson’s study. Researchers found that a single genetic mutation is responsible for a relatively large percentage of cases in the two groups under study. Within the Ashkenazim, 18 percent of diseased people carried the mutation, compared with just 1 percent of healthy people. Thirty percent of North Africans with Parkinson’s carried the mutation, compared with 3 percent of healthy people. Scientists say the surprising impact of this gene in Parkinson’s suggests that variations in this or other genes may play a role in the disease in other populations as well.
The findings also open up the possibility of genetic testing and counseling in these groups. While gene testing for diseases that have no known cure, such as Parkinson’s, is controversial, Laurie J. Ozelius, a molecular geneticist at Albert Einstein College of Medicine of Yeshiva University in the Bronx, who was involved in the research, says testing still could have some advantages. “People who come to the doctor [with symptoms of Parkinson’s] already have a lot of degeneration. Now we can look at [earlier] stages of the disease,” she says. “If we find treatments that slow the disease, it’s better to identify a gene carrier so we can start the treatment earlier.”
Susan B. Bressman, senior investigator of the report and a neurologist at Einstein, says that having a group with a known risk for Parkinson’s will aid in future studies of the disorder. Because not everyone with the mutation will go on to develop the disease, scientists can try to identify the genetic or environmental factors that put some people at greater risk. Scientists could also test potential neuroprotective drugs in this group much more efficiently than in a general population.