Incidence of Multiple Sclerosis in Multiple Racial and Ethnic Groups

Why is this study important?

Racial and ethnic minorities have long been underrepresented in western clinical studies of disease characteristics and outcomes. This has led to faulty assumptions about the frequency with which certain chronic conditions affect nonwhite individuals. For decades, multiple sclerosis (MS) has been considered a disease that affects primarily white women, with a low incidence in black communities and in other populations with darker skin tones. Previous studies comparing the risk for MS in black and white individuals were severely limited by factors such as lack of access to care in underserved communities.

A few years ago, researchers from the Kaiser Permanente Southern California Department of Research & Evaluation took a closer look at the racial distribution of MS across their health network and set out to paint a more accurate picture of the risk for MS among black, Hispanic, and Asian patients.

Which group had the highest risk for MS?

The researchers looked at the health records of more than 3.5 million members enrolled in the Kaiser Permanente Southern California health plan over a 3-year span, from January 2008 to December 2010. They identified 496 patients newly diagnosed with MS who met the clinical and MRI criteria for the disease. The majority of these patients were women (70.2%).

Overall, the likelihood of developing MS was higher among black than among white individuals. People of Hispanic and Asian descent fared better, with a lower risk for MS than white individuals. The results showed that Hispanics had a 50% reduced risk compared to white individuals, and Asians had an 80% lower chance to develop MS than white patients. These decreased odds were true for both sexes.

What was the most surprising finding?

These figures, taken from a racially diverse population, tell a surprising story: MS is still a woman’s disease, but black women are affected disproportionately. Black women included in the study were more likely to have MS compared to both white men and women, whereas black men and white men had a similar risk of developing the disease. Moreover, black women had a 3 times higher risk for MS compared with black men.

Race, ethnicity, sex, and genetic and environmental factors likely interact in shaping the risk for MS. A myriad of issues, including higher prevalence of hormonal risk factors such as fewer full-term pregnancies over a woman’s lifetime, may explain why black women are more vulnerable to this disease.  Future research may reveal more about the role of genotypes in the onset of MS.

What are the implications for minorities?

The authors noted that the results do not support the widely held belief that black individuals have a lower risk for MS than white people. While this study plays an important role in overturning assumptions, many questions about the drivers of risk in minorities remain unanswered. Individuals with darker skin tones have lower levels of vitamin D, which have been associated with an increased risk for MS. However, this does not explain why black men or individuals of Hispanic and Asian descent have more favorable odds than black women.

Additionally, the findings of the study likely underestimate the true incidence rates of MS, particularly among minorities, because some black patients with MS may be misdiagnosed and their conditions may be miscoded in health records. Projections based on the study results show that an estimated 19,000 individuals per year (or 250 per week) will be diagnosed with MS in the United States. Minorities are likely to make up a sizeable proportion of these new cases. Including minorities in MS studies in higher numbers is a critical step toward decoding the etiology of MS in racially diverse populations.

Original Article