May 28, 2004 -- A person's risk of multiple sclerosis seems to come from their mother, new data shows.
Multiple sclerosis is 20 to 50 times more common in people whose parents have the complex and poorly understood disease. But it's not a simple matter of a single gene being passed on from generation to generation. Researchers don't know whether multiple sclerosis comes from a person's genes, from a person's early environment, or from a complex interplay between the two.
Now it looks as though an important cause of multiple sclerosis may be linked to mothers. The information comes from a clever study led by George C. Ebers, MD, director of the department of clinical neurology at England's Oxford University. They compared multiple sclerosis frequency in the full-sisters and full-brothers to that of the half sisters and half brothers of people with multiple sclerosis. This study's design could help determine which parent, if either, is having an affect on multiple sclerosis risk.
They found that having a full-sister or full-brother with multiple sclerosis increased a person's risk of multiple sclerosis by 3%. Sharing only a mother with someone with multiple sclerosis increased a person's risk by a similar amount: 2%. But sharing only a father increased risk only by 1%.
"The difference in risk suggests a maternal parent-of-origin effect in multiple sclerosis susceptibility," Ebers and colleagues write in the May 29 issue of The Lancet.
Women get multiple sclerosis twice as often as men. Whether this is related to the Ebers team's current findings is not clear.
The researchers note that there are several possible explanations for the link to mothers. One is that mitochondrial genes -- genes contained in the power-generating structure in cells, which mothers pass on directly to children -- play a role in multiple sclerosis. Another theory is that multiple sclerosis is caused by imprinted genes (genes that are active only when passed on by a particular parent). Or the condition might not be genetic at all: Events that happen in the womb or during birth may play a major role.
An editorial accompanying the study comes from Mara Giordano and Patricia Momigliano-Richiardi of Eastern Piedmont University, Novara, Italy.
"Despite the new data, the nature-nurture dilemma remains," they write. "The findings of Ebers and colleagues do, however, give us some clues about directions for future research."