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Canberra (pte024/26.01.2005/12:30) - Children that live with younger siblings in their first six years are less likely to develop multiple sclerosis in later life, according to a new study. As New Scientist http://www.newscientist.com reports, the finding backs the so-called "hygiene hypothesis", which proposes that exposure to infectious bugs early in life - lurking in household dirt or carried by younger siblings - reduces the risk of allergic and autoimmune diseases by stimulating the immune system.
Multiple sclerosis (MS) is an autoimmune disease in which the body's immune system is thought to attack the fatty coat, which insulates nerve cells. Damage to this stops the nerves conducting electrical signals properly. The study, carried out by the Australian National University in Canberra http://www.anu.edu.au , showed that living with a toddler sibling for over five years could reduce the risk of developing MS by as much as 90 per cent. "This possibly occurs by altering childhood infection patterns and related immune responses," said Anne-Louise Ponsonby. According to Ponsonby, the results, if replicated, could help in understanding how to prevent MS. "It is important to emphasise that MS is a complex multi-factorial disease with both genetic and environmental factors," she added.
The team of researchers examined 136 patients diagnosed with MS and 272 healthy matched controls in Tasmania. Each volunteer was interviewed to find out more about their childhood environment. Blood samples were also taken to test for specific antibodies to certain viruses, such as the Epstein-Barr virus (EBV), which can cause glandular fever. High levels of antibodies against this virus or becoming ill with glandular fever have previously been associated with a higher risk of developing MS. The study found that people who had been exposed to younger siblings for more than five years had an 88 per cent reduced risk of suffering from MS. Those with three to five years of contact with infant siblings had a 60 per cent reduced risk, while those with one to three years living with a younger sibling have a 43 per cent reduced risk. People without MS were also less likely to have high levels of EBV antibodies.
"The new study showed that, among healthy controls, higher infant contact reduced the risk of infectious glandular fever or elevated EBV antibodies. That is, it reduced the risk of having those previously identified MS risk factors," said Ponsonby. According to Ponsonby, a possible explanation could be that repeated stimulation of the immune system by common infant infections enhances the immune response against them.
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