Multiple sclerosis, timing of birth, birth order, sibling age gap and exposure to younger siblings

Abstract

Background: Recent studies have suggested associations between the risk of developing multiple sclerosis and timing of birth or exposure to younger siblings prior to the age of 6 years. Confirmation of such findings would provide evidence for an as yet unidentified birth-related environmental factor such as early childhood infection.

Methods: As part of a national UK survey of autoimmune disease in families with multiple sclerosis we obtained nuclear family history details including date of birth for 571 case families and 351 control families. Diagnosis of multiple sclerosis was confirmed by personal review of cases using the Poser criteria.

Results: No association was seen between month of birth and risk of multiple sclerosis when compared with controls and also with UK population data for the same period. Whilst a trend towards earlier birth order was seen in cases, this was not significant and was nullified by correction for latent disease in younger siblings. Mean age gap between affected siblings (n=53) was 5.9 years compared with 5.6 years in controls (P=0.44). There was no significant difference in sibship size between case and control families. Number of years exposed to younger infant siblings in the first 6 years of life showed no significant difference between cases and controls.

Conclusions: These data suggest that risk of multiple sclerosis is not affected by season of birth or exposure to younger infant siblings, and therefore do not support a significant birth related environmental factor in susceptibility to this disease. These data are consistent with other studies.