Is sporadic MS caused by an infection of adolescence and early adulthood? A case-control study of birth order position.

Birth order position was examined in 164 cases with sporadic multiple sclerosis (MS), i.e. no other family members with MS, and spousal controls, matched for sibship size, socioeconomic status and opposite sex. The results did not find an association between birth order position and the subsequent development of MS and thus do not support the concept of an infectious cause for MS where "early exposure" is protective and exposure to the infection is a single event of short duration.