Some diseases are either more serious or more frequent in US Hispanics, and systemic lupus erythematosus is one of them. This fact has not yet diffused to all providers, many of whom will be the ones dealing with these individuals when the disease first emerges.
In order to raise physicians’ awareness of this situation, we will briefly review here the salient features of lupus in US Hispanics and its short-term and long-term impact.
HISPANICS ARE THE LARGEST MINORITY IN THE UNITED STATES
Over the last 30 years, the Hispanic population in the United States has increased to the point that it is now the largest US minority group, and the fastest-growing. In the 2010 US census, Hispanics surpassed the 50 million mark.1 Physicians and health care providers are becoming familiar with this growing population and its ailments, but more needs to be done to familiarize them with specific conditions that are more frequent and more serious in US Hispanics.
No population-based study has yet defined the prevalence and incidence of lupus in US Hispanics. However, on the basis of hospital and outpatient visits in regions in which Hispanics make up a large part of the population, it has been inferred that this group has a higher frequency of lupus, probably as high as in African Americans.
Likewise, clinicians taking care of these patients have suspected that lupus is more severe in US Hispanics than in non-Hispanic Caucasians, but this was documented and brought to general attention only with the publication of reports from the Lupus in Minorities: Nature versus Nurture (LUMINA) study.2
LUMINA, a longitudinal study
LUMINA is a longitudinal study of 640 patients with lupus from four populations: Hispanic from Texas, Hispanic from Puerto Rico, African American, and Caucasian non-Hispanic (Table 1). At the time of recruitment, patients were at least 16 years old and had had lupus for 5 years or less. They come in for periodic visits to the University of Alabama at Birmingham, the University of Texas Health Science Center at Houston, and the University of Puerto Rico Medical Sciences Campus. Recruitment began in 1994 and finished in 2007. Follow-up ranges from 1 to 14 years, with a mean of 4.5 years.
LUMINA is supported by grants from the National Institute of Arthritis and Musculoskeletal and Skin Diseases, the National Institutes of Health General Clinical Research Centers program, the National Center for Research Resources Clinical Research Infrastructure Initiative, the Mary Kirkland Center for Lupus Research Scholars Program, and Rheuminations Inc (New York, NY).
The purpose of the study is to shed light on the interplay of genetics and environment in this disease and, in the process, to raise awareness about the problem of lupus in Hispanics. In fact, much of the information in the following sections is from the LUMINA study.
HISPANICS ARE NOT A HOMOGENEOUS GROUP
In the United States, the term Hispanic describes anyone whose origin goes back to a Spanish-speaking country. However, US Hispanics are not a homogeneous racial group: they differ in genetics, culture, and problems.
The largest US Hispanic subgroup and the one more likely to be seen by US physicians is Hispanics of Mexican origin, who account for 66% of all US Hispanics. This group has a higher percentage of Amerindian genes than those of Puerto Rican ancestry.3 LUMINA researchers analyzed the DNA of 492 patients and found the following mixtures of genes3:
- Hispanics in Texas (mostly of Mexican origin): 48% Amerindian, 18% African, 34% European
- Hispanics from Puerto Rico: 20% Amerindian, 45% African, 35% European
- African Americans: 0% Amerindian, 79% African, 21% European
- Non-Hispanic Caucasians: 10% Amerindian, 18% African, 72% European.
Latin Americans of mixed European and Amerindian ancestry (which includes Aztec, Mayan, Quechuan, Aymaran, and other Central and South American groups) are called mestizos. Not all people in Latin America are mestizos: some are of European, African, or Asian ancestry, but in the United States they are all called Hispanics.
LUPUS DIFFERS AMONG SUBGROUPS
LUMINA research has revealed that lupus is heterogeneous also among US Hispanic subgroups. When people from Puerto Rico get lupus, it is generally less serious and devastating than in those from Mexico or Central America. Since US Hispanics of Mexican or Central American origin possess more Amerindian genes, this observation supports the notion that these genes are important contributors to the occurrence and expression of the disease.
Amerindian genes contribute to a greater susceptibility to lupus,4,5 although there is an interplay between genetic and nongenetic factors in the etiology and expression.6 Lupus starts at a younger age in Hispanics of predominantly Amerindian ancestry than in non-Hispanic Caucasians, and the onset is more likely to be acute.7
Renal involvement in these patients8 and mestizos from Latin America is rather common, probably as common as it is in US African Americans, and it tends to develop earlier than in non-Hispanic Caucasians.9 Amerindian ancestral genes, like African genes, contribute to the occurrence of renal disease in lupus patients.4 Furthermore, once nephritis ensues, end-stage renal disease occurs more often in US Hispanic and African American than in non-Hispanic Caucasian children, as demonstrated by Hiraki et al10 using national databases, and the same is true in adults, as shown in the LUMINA cohort.11
Other potentially serious manifestations of the disease are also more common, including hematologic and central nervous system manifestations. Not surprisingly, then, these patients show a higher degree of disease activity, both early in the course of the disease12,13 and over time.14
Table 1 compares the demographic and clinical features of LUMINA patients according to ethnicity. By and large, Hispanics from Texas have lower levels of education and income (comparable with levels in African Americans), and this can adversely affect the disease course by limiting these patients’ access to adequate care.15
DISEASE ACTIVITY AND ORGAN DAMAGE ARE GREATER IN HISPANICS
Disease activity in lupus reflects the ongoing immune-mediated inflammatory process. In LUMINA patients, regardless of the time at which disease activity was ascertained, it was higher in Hispanics from Texas and in African Americans than in non-Hispanic Caucasians and in Hispanics from Puerto Rico.7,12,16–18 Similar findings were seen in the Grupo Latinoamericano de Estudio de Lupus (GLADEL) cohort,13 in which mestizos and Hispanics of mixed African and European ancestry had higher maximum disease activity scores than non-Hispanic Caucasians.13
In addition, organ damage in lupus—the irreversible changes that occur in organ systems as a consequence of the disease or its treatments (eg, glucocorticoids, immunosuppressive drugs)—is more severe and develops sooner in Hispanics from Texas than in other groups.6,18,19 Using multivariate analysis, LUMINA investigators19 estimated the hazard ratio for the time until organ damage appeared for various risk factors, with values of 1 or greater indicating a shorter time and lower values indicating a longer time. Being a Hispanic from Texas carried a hazard ratio of 2.11 (95% confidence interval 1.15–3.88).
Because organ damage is an important and independent predictor of further damage20 and death,21 physicians need to take this disease quite seriously and try to prevent damage early in people at risk. To achieve that, the need to control disease activity must be balanced against the risk of overtreatment, as the important contribution of glucocorticoids to organ damage is well recognized.22