Birth order and risk of multiple sclerosis: Are they associated and how?

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Abstract
By analyzing birth order distribution in 107 patients with multiple sclerosis, a positive association is found between birth order and risk of multiple sclerosis. Conditionally to the number of siblings in the 107 families, patients’ mean birth order is significantly greater than expected. The number of patients whose birth order is equal to one is significantly smaller than the corresponding expected value. The present finding is in contrast to recent results observed by Isager et al. (1980) and this potential association deserves to be further investigated.