New population-based research indicates African-Americans may face a higher risk of developing multiple sclerosis (MS) than Caucasians, challenging long-held assumptions.
Overview of the study
A study published in the May 7, 2013 print issue of the journal Neurology examined MS incidence across a large, diverse health plan population and found notable differences in risk by race and sex. Conducted by researchers at Kaiser Permanente Southern California, the investigation used a population-based approach to provide a more comprehensive estimate of MS risk than clinic-based studies.
Study design and data
Researchers analyzed the health records of more than 3.5 million Kaiser Permanente Southern California members over a three-year period to identify newly diagnosed cases of multiple sclerosis. Using this large, population-based sample allowed the team to capture cases across the health system rather than relying on data from a single clinic or referral center, which can introduce selection bias.
Key findings
The researchers identified 496 people with newly diagnosed multiple sclerosis. Compared with Caucasian members of the study population, African-Americans had a 47 percent higher risk of MS. In contrast, Hispanics and Asians showed substantially lower risks—58 percent and 80 percent lower, respectively, than Caucasians.
Sex differences emerged in the analysis. The elevated risk among African-Americans was driven primarily by women: African-American women had approximately three times the risk of MS compared with African-American men. The lower risk observed in Hispanic and Asian groups applied to both sexes.
Population distribution
Examining the composition of the study population clarified these disparities: African-Americans represented 21 percent of those diagnosed with MS, though they comprised only 10 percent of the overall population studied. Caucasians made up 52 percent of MS cases versus 38 percent of the total population. Hispanics accounted for 23 percent of MS cases but 40 percent of the overall population, and Asians represented 3 percent of MS cases compared with 9 percent of the population.
Possible explanations and limitations
One hypothesis offered by the authors is that differences in vitamin D levels, which can be affected by skin pigmentation and sun exposure, might contribute to risk variation. However, the vitamin D explanation does not fully account for why Hispanic and Asian groups had lower risk than Caucasians, and the study authors cautioned that multiple biological, environmental, and social factors could influence these findings.
Because the study is observational, it cannot establish cause and effect. The authors emphasize the need for further research to clarify the mechanisms behind racial and ethnic differences in MS risk, including studies that measure vitamin D and other potential risk factors directly and that include diverse populations in genetic, clinical, and environmental analyses.
Implications
These results underscore the importance of including minorities in MS research and clinical trials. If African-American women are at relatively higher risk, targeted awareness, earlier diagnosis, and better access to care may help address disparities in outcomes. The findings also suggest clinicians should consider demographic and social determinants when evaluating patients with early neurological symptoms.
Notes about this multiple sclerosis research
The study was supported by the Kaiser Permanente Community Benefits Fund.
Contact: Rachel Seroka and Michelle Uher – American Academy of Neurology
Source: American Academy of Neurology press release
Image source: Public domain diagram of multiple sclerosis symptoms
Original research: Abstract for “Clinical and Demographic Predictors of the Risk of Conversion from Clinically Isolated Syndrome to Multiple Sclerosis: A Population-Based Study” by Annette Langer-Gould and Jian Zhang in Neurology. Published online February 12, 2013.