Birth order does not affect multiple sclerosis risk

Reported by Susan Aldridge, PhD, medical journalist

A study shows that older siblings do not, as had previously been believed, run a higher risk of multiple sclerosis.
It's been suggested that both environmental and genetic factors play a role in multiple sclerosis (MS). In previous research, more cases have been found in small families and in eldest children. One possible reason for this is the so-called hygiene hypothesis - exposure to infection reduces the risk. Such exposure is less in a small family and, maybe, for the older siblings.

Canadian and British scientists analyzed data from nearly 11,000 individuals with MS and other 26,000 healthy siblings. Overall, no link was found between risk of MS and birth order position. In large families, those who went on to develop MS actually seemed to be born later - rather than earlier. The findings suggest that maybe other environmental factors are relevant in MS, but the hygiene hypothesis may not be valid.

Source
The Lancet Neurology online 22nd August 2005

Please take a moment to give us your comments. For questions about Health matters you may check our "Questions & Answers" Portal and Service.