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Having younger siblings helps prevent MS.

The study found that increasing amounts of time spent in contact with a younger sibling aged less than two years in the first six years of life was associated with reduced risk of developing MS, possibly by altering childhood infection patterns and related immune responses.

Dr Ponsonby said participants who had had one to three years of cumulative contact with any younger sibling had a 43 percent reduced risk; three to five years of contact a 60 percent decreased risk; and greater than five years of contact an 88 percent reduced risk of MS.

The study, conducted in Tasmania from 1999 to 2001, involved more than 400 participants. Researchers surveyed 136 patients with MS and 272 people without MS (control group) about their number of siblings and dates of birth, whether the sibling lived in the same house as the participant, and other factors thought to be associated with MS. Blood samples were taken to measure levels of antibodies to the Epstein-Barr virus (EBV), a common childhood infection.

Past work has shown that two major risk factors for developing MS are a history of glandular fever, and higher levels of antibodies to EBV.

Dr Ponsonby said: “Healthy participants in this new study who had contact with younger siblings aged from birth to two years were less likely to have a history of glandular fever or higher EBV antibodies. That is, they were less likely to have these risk factors.”

“It has been proposed that early life infections may reduce the risk for allergic and also autoimmune disorders such as MS, by influencing the developing immune system. Having siblings may increase the number of early-life infections, and a lack of contact with siblings has been associated with several immune disorders.

“Younger siblings may be important because they are a source of common childhood viral infections. Re-exposure to active viral infection is known to cause immune boosting and train immune responses”, she said.

The possible protective role of early life infection in the development of MS is in line with increasing prevalence of the disease, which has accompanied a decline in childhood infection rates over time.

“Further work is required to confirm these findings and understand the underlying mechanisms. This is another piece of the jigsaw in the understanding and work towards future prevention of MS”, said Associate Professor Ponsonby.

Multiple Sclerosis (MS) is a chronic inflammatory disease of the brain and spinal cord that leads to various degrees of disability. Symptoms may range from tingling and numbness to paralysis and blindness. Twice as many women as men have MS, with the onset of symptoms occurring most often between the ages of 20 and 40.

This project was supported with funding from the National Health and Medical Research Council of Australia, the Australian Rotary Health Research Fund, and MS Australia.