Multiple Sclerosis in the Hispanic/Latinx Population

Multiple sclerosis (MS) is an immune-mediated disease with etiology that seems to be multifactorial. Studies have reported the presence of several alleles against the development of autoimmune diseases. Environmental factors, genetics, and social determinants, including racial and ethnic identities) play essential roles in the geographic distribution of MS, although studies confirm the importance of environmental agents as an independent variable not associated with ethnic identity.

The terms Hispanic and Latino are sometimes used interchangeably in the literature, but Hispanic, historically, refers to people born in the regions of the Americas colonized by Spain. Latino refers to people with ancestral and cultural ties to Latin America.¹ The term Latinx is a newer gender-neutral or nonbinary alternative to Latino or Latina to refer to a person of Latin American origin or descent. There is a great diversity amongst Hispanic/Latinx individuals, including Amerindian people (the indigenous populations that inhabited the region before European conquest), Black people (Africans brought to the region as slaves and their descendants), and white people (European colonists who conquered and settled the region and their descendants). In addition, these populations have blended.¹ Diversity of culture also exists amongst and even within regions where people reside, comprised by the large area that is North America, South America, Latin America, and the Carribbean.

Epidemiology

Incidence of MS in Hispanic/Latinx people varies widely (Table).^2-9 A retrospective cohort study from the Kaiser Permanente plan in Southern California reported an incidence among individuals identified as Hispanic of 2.9 per 100,000 vs 6.9 per 100,000 in individuals identified as white.² The Hispanic/Latinx population in the US has a higher incidence of MS compared with some populations in some countries of their ancestral origins. In 2012 in a large sample of Lacandonian individuals who underwent comprehensive clinical and neurologic testing showed an absence of MS and neuromyelitis optica spectrum disorders (NMOSD) in this Amerindian group in Mexico considered as having unmixed ancestry.³

In Latin America and the US, prevalence of MS is variable (Table).^3-9 Notably, incidence and prevalence in Puerto Rico are higher than in many Latin American countries. Reasons for the low prevalence of MS in Latin America have not been identified, but genetic and environmental factors may play an influential role. Although MS is still more common in regions further away from the equator, increased incidence has been reported in countries that previously had lower prevalence.^4-8

Recent reports show increasing frequency of MS in Latin America and globally, which could result from multiple factors, including increased access to MRI for diagnosis and increased medical education and awareness for medical practitioners and neurologists.^4-10 There was an approximately 30% to 40% increase in the age-standardized prevalence of MS in Latin America and the Caribbean from 1990 to 2016.^9,10

Genetic Risk of MS in the Hispanic/Latinx Population

Studies in Mexico have shown that people with MS who have combined ancestry from both indigenous Amerindians and Spaniards share an HLA-DRB1 profile similar to that of Europeans. Alleles associated with increased MS risk in Latin America include DRB1*1501 with an odds ratio (OR) of 2.6, DQB1*0602 (OR 2.5), DRB1*15 (OR 2.3), DQB1*06 (OR 2.2), and DRB1*1503 (OR 2.2).¹¹

The presence of 1 or more of these risk alleles varies widely among Latin Americans. The DRB1*1501 allele is found primarily in people with European ancestry and is more prevalent in Argentina and Uruguay. Brazilians with African ancestry who have MS share some European alleles associated with MS susceptibility in Europeans and Afrocaribbeans, such as DQB1*0602, but do not share the DRB*1501 allele common in Brazilian white people, Europeans, and Americans with African ancestry. DRB1*1503 is found in people with African ancestry in the Caribbean and Americas.^12,13

Environmental Factors

Other unique environmental factors may also help explain the lower frequency of MS and other autoimmune disorders in Latin America. Exposure to environmental pathogens such as parasites may have a protective effect, suppressing the development of MS, as suggested by the hygiene hypothesis.¹⁴ Other factors include vitamin D and sun exposure.¹⁵ These environmental factors may be different in Hispanic/Latinx individuals, in particular, those born in the US.

MS in Hispanic/Latinx People in the US

Hispanic Americans/Latinx individuals living with MS in the US are a diverse group from many different cultural and ancestral backgrounds, and some are more likely to have socioeconomic barriers that can interfere with access to adequate MS care. Hispanic representation in clinical trials in the US presents a unique set of challenges for public health practitioners, including language barriers, concerns about immigration status, and different cultural views on the benefits of medical care. Hispanic individuals account for only 7.6% of participants in clinical trials although according to 2010 census data they comprise 18.5% of the US population.

There also seems to be a higher proportion of disease severity in this group, particularly in male individuals.¹⁵ This may be related to comorbidities and other genetic factors that have not been fully elucidated yet. Higher prevalence of MS is observed in Hispanic/Latinx people in the US compared with Latin America, because of acculturation, which refers to assimilation of a different culture that can affect dietary habits and activity levels as well as environmental exposure to different pathogens. Moreover, accessibility to MS specialists and advance neuroimaging may lead to underestimate of the prevalence in Latin America as well.

Other contributing factors may include the gut microbiome, for which emerging evidence suggests a relationship with immune-driven diseases such as MS. Microbiome alterations could lead to differences in disease severity and response to medications.¹⁶ In people in the US with a new diagnosis of MS who were treatment-naive, 3 ethnic groups were compared, and significant differences were seen in the beta-diversity of the gut microbiome in Hispanic/Latinx individuals with vs without MS.¹⁷ More studies regarding gut microbiome and ethnicity are needed to be able to make any conclusions.

Latin Americans with African ancestry with relapsing-remitting MS have been reported to have a higher risk of transition to secondary progressive disease.² Other research suggests response to treatment, in particular interferon Β, is less optimal in Black and Afrocaribbean people (see Multiple Sclerosis in the Black Population in the United States).¹⁸

Compared with white people, Hispanic/Latinx people have lower enrollment rates for clinical trials. Therefore, the generalization of the trial results to Hispanic/Latinx population should be done carefully. Data from the North American Registry for Care and Research in Multiple Sclerosis showed that Hispanics and individuals from other populations that have been historically minoritized in North America are less likely to be treated with a disease-modifying therapy (DMT).¹⁹ The Latin American MS Expert Forum also reported a suboptimal response to DMT among Hispanic individuals.²⁰ This may be a factor leading to poor clinical outcomes in the Hispanic/Latinx population; early diagnosis and early aggressive treatment, may positively affect clinical outcomes.

Adherence to treatment by people from historically minoritized populations is a focus of interest. A retrospective study evaluated adherence to fingolimod vs glatiramer acetate treatment by Hispanic individuals with MS found both Hispanic and Black individuals who began therapy with fingolimod had higher adherence to treatment than those who started with glatiramer acetate.²¹ More extensive studies are needed to evaluate the lower response of and less adherence to certain DMTs in Hispanic/Latinx individuals.

Conclusion

Hispanic/Latinx individuals living with MS are a diverse group in which genetic background and multiple environmental factors may play a role in the prevalence of disease as well as the response and adherence to DMTs. The severity of disease seems to be higher in this population. More studies are necessary to describe the clinical, genetic diversity, and environmental factors that may be involved. In addition, having a better understanding of the cultural, economic, and social barriers may lead to a more comprehensive approach to MS care for Hispanic/Latinx patients in the US.