In an article in the Journal of Neurology, Neurosurgery and Psychiatry, Dr. Christopher H. Hawkes of the Institute of Neurology in London states that certain genetic factors make some people susceptible to a sexually transmitted agent that triggers multiple sclerosis. He does not claim, however, that the disease is always contracted sexually.
But other MS experts were skeptical about the notion, which they said does not have a sound scientific grounding.
"I think the hypothesis is of low credibility," Dr. Graeme Stewart of the University of Sydney in Australia told Reuters Health.
The report, according to Stewart, who is the author of an accompanying editorial, "is not based on original research but is derived from a selective interpretation of old studies" that were carried out for different purposes. It is also based, at least in part, he said, "on assumptions of sexual behavior that are not supported by direct data and that are not particularly credible."
The report is "speculation," according to Dr. Lauren Krupp, a professor of neurology at the State University of New York at Stony Brook. The hypothesis is "really not supported" by scientific evidence, Krupp, who is a spokeswoman for the National Multiple Sclerosis Society, told Reuters Health in an interview.
In MS, the slow destruction of myelin--the thin, protective coating that insulates nerve fibers in the brain and spine--can lead to numbness, muscle weakness and stiffness, impaired vision and coordination problems.
No one knows what causes MS, but both heredity and environment are thought to be involved. About 5% of people with MS also have a sibling with the illness and about 15% have another close relative with the disease. Geography is one environmental factor that seems to come into play. About 1 out of every 2,000 people in temperate climates have MS, compared with just 1 out of every 10,000 people in tropical areas.
Hawkes proposes that "multiple sclerosis is a sexually transmitted infection acquired principally during adolescence and mainly from infected and not necessarily symptomatic males."
In the report, Hawkes cites two types of migration studies to support the hypothesis. It is generally accepted, he states, that moving from a high-risk to a low-risk area--a colder climate to a warmer one--before age 15 lowers the risk of developing MS. And he points out that the reverse situation--people moving from low- to high-risk areas--increases the risk of MS.
"These studies are supportive of an environmental factor and raise the possibility that the risk of multiple sclerosis is established in the teenage years, the time of sexual debut," Hawkes writes.
The UK researcher also cites several clusters and epidemics of MS that occurred in Iceland, the Orkney and Shetland Islands and other locations after foreign troops, who likely had sexual contact with some residents, were stationed there.
Adding to the evidence linking MS to a sexually transmitted infection, according to Hawkes, is that symptoms of the disease are similar to those of a sexually transmitted disease called tropical spastic paraplegia.
Cultural factors also support the idea that MS is sexually transmitted, Hawkes states. He notes that MS is more common in cultures that have more permissive attitudes toward sex. Hawkes also suggests that the low rates of MS in certain groups, including the Maoris in New Zealand and Native Americans, may stem not from genetic differences but from the fact that these cultures have less social interaction with other groups.
To support his claim, Hawkes also notes that the percentage of MS patients who were women began to climb in the early 1970s, when the use of oral contraceptives was increasing. This trend supports a sexually transmitted MS agent, according to Hawkes, because presumably women taking the Pill would be less likely to use barrier methods of birth control, such as condoms, that would block the spread of a sexually transmitted infection.
The report does not prove that MS is sexually transmitted, but it "provides a testable hypothesis," Hawkes said.
According to Krupp, the spokeswoman for the National MS Society, the concept that environmental factors affect MS risk is not new. There are indications that exposure to any of a number of viruses, including the measles virus, which is not sexually transmitted, may affect MS risk, Krupp said, but there is scant evidence for the idea that MS is spread sexually. The report, she said, "does not in any way" suggest that people with MS should abstain from sex with their partners.
SOURCE: Journal of Neurology, Neurosurgery and Psychiatry 2002;73:358-359, 439-443.