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Establishing that there are gestation-related risk factors for multiple sclerosis (MS) significantly impacts our understanding of the timing of environmental risk in MS and ultimately would have a critical influence on prevention strategies. One such factor—month or season of birth—has been reported1- 3 to be associated with risk of MS and other diseases, such as asthma and type 1 diabetes mellitus, as well as overall lifespan. Prior studies4- 7 have demonstrated a higher risk for MS in infants born in the spring, whether in the Northern or Southern hemispheres. Recent work8- 10 has questioned these associations based on unaccounted-for biases from birth patterns in the general population. Concern has centered on the concept that birth rates are not homogeneously distributed throughout the year and may vary by region or latitude within a country. Seasonality has been shown8 to be more prominent with higher birth rates in the spring in countries or regions farther away from the equator. Because the frequency of MS is well known to vary by latitude, these regional birth rates may cause false association of birth month and MS risk.
Graves JS. Is Season of Birth Important for Multiple Sclerosis Risk?. JAMA Neurol. 2016;73(8):912-913. doi:10.1001/jamaneurol.2016.1763