Growing up with baby brothers or sisters may have a protective effect against the development of multiple sclerosis (search).

It’s possible but not certain, says Anne-Louise Ponsonby, PhD. She works at the Australian National University and has studied MS, a disease of the brain and spinal cord. MS symptoms include problems with muscle control and strength, vision, and balance.

No one knows what causes MS. Genetics might be involved, since people with family members that have MS are at a higher risk for the disease. Environmental factors such as viral illnesses (search) and other infections may also play a role in the development of the disease.

How might babies help protect their big brothers and sisters from MS? The answer could be the infections infants often get during their first two years of life. When babies become infected, their older siblings can also be exposed, strengthening their immune systems, say the researchers.

It is thought that MS is an autoimmune-driven disease; people with this disease have an altered immune system which mistakenly attacks nerve fibers of the brain and spinal cord.

However, there is no clear proof that any specific infection triggers the autoimmune disease (search) to develop.

Ponsonby and colleagues studied more than 300 Australians, reporting their findings in the Jan. 26 issue of The Journal of the American Medical Association.

Participants were 136 adults with MS and 272 without MS. All were about 43 years old. Brain scans (MRI) confirmed MS cases by showing distinct lesions seen in people with MS.

More Babies, Lower Risk

Those with at least one baby sibling before age 6 were less likely to have MS as adults.

The more time participants spent before age 6 with baby brothers or sisters, the less likely they were to have MS as adults.

For those with one to three years of infant contact before age 6, MS risk was 43 percent lower. Those who were around baby siblings for three to five years before age 6 had a 60 percent drop in MS risk. The greatest reduction in MS risk — 88 percent — was among people with five or more years of exposure to baby siblings before age 6.

For people with MS, infant exposure was linked to a delayed onset of the disease.

Benefits were only seen with younger siblings less than 2 years old.

Researchers call for more studies to confirm the findings.

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Ponsonby, A. The Journal of the American Medical Association, Jan. 26, 2005; vol 293: pp 463-469. WebMD Medical Reference from Healthwise: “Multiple Sclerosis (MS) — Topic Overview.” WebMD Medical Reference from Healthwise: “Multiple Sclerosis (MS) — Cause.” WebMD Medical Reference from Healthwise: “Multiple Sclerosis (MS) — What Increases Your Risk.” News release, JAMA and Archives Journals.