DALLAS – Latitude continues to be associated with the prevalence of multiple sclerosis (MS), according to an updated meta-analysis presented at ACTRIMS Forum 2019, held by the Americas Committee for Treatment and Research in Multiple Sclerosis.
Dr. Steve Simpson Jr.
After integrating data from 94 new studies, “the latitudinal gradient in MS prevalence ... significantly enhanced in magnitude,” said presenting author Steve Simpson Jr., PhD, and his colleagues. Dr. Simpson is a researcher at the Melbourne School of Population & Global Health at the University of Melbourne and the Menzies Institute for Medical Research at the University of Tasmania.
The researchers’ original study, published in 2011, found a slope of 2.68.
Latitudinal variations in MS prevalence have given credence to the theory that sun exposure and vitamin D may play a role in MS onset. The researchers’ original meta-analysis – based on 650 prevalence estimates from 321 studies – “confirmed the existence of a robust latitudinal gradient,” they said. To examine whether the gradient has changed, the researchers identified relevant studies published between 2010 and 2018.
They included complete, peer-reviewed articles in their analysis and extracted data about the study area, prevalence year, MS diagnostic criteria used, sample size, source population, crude prevalence, and age-specific prevalence. They combined the new prevalence estimates with those from their original study. The estimates were log-transformed and weighted with the inverse of the variance. In addition, the researchers used random-effects meta-regression models that adjusted for prevalence year and method of case ascertainment.
Their literature review identified 126 new studies, 94 of which met inclusion criteria. The new studies yielded 230 additional prevalence points, predominantly in Scandinavia, France, and the Middle East.
“Latitude was consistently and significantly associated with MS prevalence in all analyses, increasing in magnitude on adjustment and persisting on age-standardization,” Dr. Simpson and his colleagues reported.
By region, strong and significant positive gradients continue to exist in Australasia, the United Kingdom/Ireland, and North America. Meanwhile, a significant inverse gradient continues to exist in the Italian region, which the researchers have said relates to the frequency of an MS-related HLA-DRB1 allele there. A negative gradient in the Scandinavian/North Atlantic region in the original meta-analysis, considered potentially related to dietary differences, was “markedly reduced” and no longer statistically significant in the updated meta-analysis.
“While there are potential intra-regional effects contributing to the latitudinal variation in MS prevalence, these results and the relative consistency across the whole of the globe continue to provide indirect evidence in support of the role of sun and vitamin D in MS etiology,” Dr. Simpson and his colleagues concluded.
The researchers had no disclosures.
SOURCE: Simpson S Jr et al. ACTRIMS Forum 2019, Abstract 126.