Among patients of European descent, higher latitude regions are associated with an earlier age at onset of multiple sclerosis (MS), according to data published online ahead of print November 3 in the Journal of Neurology, Neurosurgery and Psychiatry. Age at MS onset also is lower among people with less exposure to ultraviolet radiation.
Bruce V. Taylor, MBBS, Professorial Research Fellow at the University of Tasmania, Australia, and his collaborators examined data for 22,162 eligible patients participating in the international MSBase Registry. Eligible participants had MS, were age 16 or older, and came from centers of largely European descent. The investigators defined age at onset as the year of the first symptom suggestive of inflammatory CNS demyelination. They evaluated predictors of age at onset using linear regression.
Bruce V. Taylor, MBBS
Most patients in the sample were women (70.4%) and had relapsing-remitting MS (91.5%). In addition, most participants were from the northern hemisphere (81.4%), particularly Europe (67.2%), and a large proportion (15.7%) were from Australia. The sample’s mean age at MS onset was 32.3.
In the univariable analysis, latitude as a continuous linear factor was significantly negatively associated with age at onset. Every 10° increment of latitude was associated with a 0.3-year earlier onset. After adjustment for relevant covariates, patients of the highest latitude stratum had MS onset nearly 1.9 years earlier than patients of the lowest latitude stratum. In an evaluation of latitude as a continuous variable in the multivariable analysis, a 10° increase in latitude was associated with a 0.82-year earlier onset.
A similar pattern emerged for exposure to ultraviolet light. After adjustment for confounders, the investigators found a dose-dependent association between ultraviolet B and age at MS onset. In the multivariable analysis, people with the lowest ultraviolet B exposure had MS onset nearly two years earlier than people with the highest ultraviolet B exposure.
After adjustment for variables, age at MS onset was 0.43 years lower among women than among men. The latitudinal gradient of age at onset was not significantly different between men and women. Birth dates were evenly distributed in all four seasons, and the researchers found no association between season of birth and age at onset.
—Erik Greb
Suggested Reading
Tao C, Simpson S Jr, van der Mei I, et al. Higher latitude is significantly associated with an earlier age of disease onset in multiple sclerosis. J Neurol Neurosurg Psychiatry. 2016 Nov 3 [Epub ahead of print].