New study suggests connection between MS and the environment.

While scientists do not know all of the risk factors for developing MS, it is generally believed that genetics, geography, and an as-yet unknown environmental factor, such as a bacteria or vires, might each have a role.

A new study may point to an environmental trigger for MS.

MS and emigration 

Dr. R Cabre and colleagues at Le Centre Hospitalier Universitaire de Fort-De-France, Martinique, have been studying a recent rise in MS on the islands of Martinique and Guadeloupe.

During the 1950s and 1960s many people emigrated from these islands to France. Many have since returned. Dr. Cabre and his team found the prevalence of MS was twice as high in people who had returned to the islands as in people who never left. It was especially high if the person left before the age of 15.

The study was published in the September 23, 2005, issue of Brain.

The authors propose several explanations, including the idea that intestinal parasites may once have played a protective role. Dr. Cabre's team notes that the rate of intestinal parasites on the islands dropped from 70% in 1978 in children aged 5 to 15, to just 8% in 1994. Immune-system defenses against parasites may have prevented the over-active immune response characteristic of MS.

One of the alternative explanations is that MS was triggered by exposure to something in the environment while the individuals lived in France.

Further study is needed to explore the surprising increase of MS on Martinique and Guadeloupe--research that may reveal important clues to the cause of MS.