People with younger brothers and sisters may face a lower risk of developing multiple sclerosis, suggests a new study published this month in the Journal of the American Medical Association.1
The Family Connection
Medical researchers in Australia followed more than 400 adults, and compared their exposure to younger brothers and sisters under age 2 in the context of MS risk. The physicians took MRI (magnetic resonance imaging) scans of each person's brain to confirm MS. One hundred thirty-six patients with the disease were compared in terms of exposure to a younger sibling with 272 people without MS matched for age and year of birth.
Contact with siblings before age 6 was the key focus, as this is a time in which children very frequently encounter other kids at school.
"Increasing duration of contact with a younger sibling aged less than 2 years in the first 6 years of life was associated with reduced MS risk," wrote lead study investigator Anne-Louise Ponsonby, PhD, who works in the National Centre for Epidemiology and Population Health at The Australian National University in Canberra, Australia. Children exposed to their siblings for 1 to 3 years (before age 6) was associated with a 43% reduced risk of developing MS, the researchers found. But for those with contact with their younger siblings for more than 5 years, the risk was 88% lower.
The scientists also compared the risk of acquiring Epstein-Barr virus between people who had less or more contact with younger siblings, and found the same trends. It's hypothesized that the cause of MS may be due to a viral infection like that caused by the Epstein-Barr virus, although the evidence is inconclusive.2
'Hygiene Hypothesis'
Why is this? Ponsonby and her colleagues suggest that it may be due to the "Hygiene Hypothesis". Immune reactions form early in childhood, and so, children exposed more often to a variety of germs by coming into contact with younger siblings tend to develop more antibodies against them. Thus, their immune system may help protect them in this way against MS later in life.
Experts say exposure to older siblings does not provide the same protective effect because older children have fewer germs, and thus they're not passing as many of these disease-causing organisms on.
Origins of the Disease
Multiple sclerosis is thought to have afflicted approximately 400,000 Americans. Each week, another 200 people are diagnosed. It's believed to be an autoimmune disease, centered around an abnormal immune system attack against the body's own tissues. One key target of this attack is myelin, a fatty tissue that protects nerve endings in the central nervous system.
Myelin allows nerve fibers to conduct electrical impulses between each other, but when it is stripped away, the fibers become damaged and unable to communicate among each other. As a result, the symptoms seen in MS appear. There are four key forms of the disease:
• Relapsing-remitting MS
• Primary-progressive MS
• Secondary-progressive MS
• Progressive-relapsing MS
Relapsing-remitting multiple sclerosis is the most common form, affecting an estimated 85 percent of people with the disease.
1. Ponsonby AL, van der Mei I, Dwyer T et al. Exposure to infant siblings during early life and risk of multiple sclerosis. JAMA 2005 Jan 26;293(4):463-9.
2. National Multiple Sclerosis Society. Viruses. Available at: http://www.nationalmssociety.org/Sourcebook-Viruses.asp. Accessed February 4, 2005.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include coverage of health news for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
