According to a study published in the January 2005 issue of Journal of the American Medical Association exposure to an infant sibling in the first 6 years of life was associated with a reduced risk of multiple sclerosis (MS) among 408 people studied in Tasmania, Australia. A history of exposure to infants was also associated with reduced reactivity to certain infectious agents. The authors suggest that this study may strengthen the idea––known as the “hygiene hypothesis”––that exposure to infections early in life may alter immune activity and decrease the risk for disorders such as MS that involve an autoimmune attack.

Dr. Anne-Louise Ponsonby and her colleagues from The Australian National University in Canberra interviewed 136 people with MS and 272 people without the disease between 1999 and 2001. The interview included questions on number of siblings and their dates of birth, whether siblings lived in the same house, and illness history. The authors also drew blood samples to determine the presence of immune-system antibodies to Epstein-Barr Virus (EBV), indicating prior exposure to a virus that can cause infectious mononucleosis and other disorders and which in some studies has been linked to the risk of MS.

The results suggest that the longer people (in the first 6 years of life) were cumulatively exposed to any siblings younger than 2 years, the more reduced their risk of developing MS. Exposure to infant siblings also was associated with a reduced response to EBV in people who did not develop MS. Also, among the 272 individuals without MS, 1 year of exposure to an infant was associated with a reduced risk of developing mononucleosis when they were older. In 2003, this group had reported evidence that increased sun exposure during ages 6 to 15 was associated with a decreased risk of MS, so in the current study, they investigated past sun exposure as well. They found that the association between having younger siblings by age 6 years and reduced risk of MS was significantly stronger in people who had higher winter sun exposure during childhood.

This study takes an interesting approach to investigating whether early exposure to infectious agents, in this case to infant carriers of such agents, is “protective” against the development of MS. The authors note that further work is necessary to confirm these findings, and to determine possible underlying mechanisms whereby childhood infection or sun exposure may trigger immunomodulation. (Available from:
http://www.nationalmssociety.org/Research-
2005Jan31.asp

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