From the Cerebrovascular Program, Department of Neurology, Indiana
University School of Medicine, Indianapolis.
Correspondence to Askiel Bruno, MD, Neurology Department, 541 Clinical Dr, Room 365, Indiana University School of Medicine, Indianapolis, IN 46202-5111.
The study of disease
differences between ethnic and racial groups is complicated by the
genetic, environmental, and cultural heterogeneity
within each group. Despite these complications, the study of
well-defined groups of people can yield medical information useful to
improve health in these groups. For example, moyamoya disease has a
predilection for Japanese people, the incidence of stroke is higher in
blacks than in whites,1 and occlusive cerebrovascular
lesions are more likely to be intracranial in blacks than
whites.2 3 4 This information can be used to optimize risk
factor screening and management, acute stroke treatment, and secondary
stroke prevention in the various ethnic and racial groups.
Relatively little is known about cerebrovascular disease in
Hispanics and Native Americans in the southwestern United States.
Hispanics constitute
Differences in vascular risks have been measured between US Hispanics
and non-Hispanic whites. US Hispanics appear to have a lower prevalence
and severity of arterial hypertension and lower levels of
serum cholesterol but higher prevalence of diabetes
mellitus, tobacco smoking, and obesity than non-Hispanic
whites.5 These differences in vascular risks may lead to
variances in the manifestation of cerebrovascular disease between
Hispanics and non-Hispanic whites. The incidence of
intracerebral hemorrhage6 and
subarachnoid hemorrhage7 in central New
Mexico is significantly higher among Hispanics than non-Hispanic
whites. The reasons for these differences have not been investigated.
It is important and interesting to observe that Hispanics in New York
City, who have different ancestry than Hispanics in New Mexico, also
have an increased incidence of hemorrhagic strokes as compared with
whites.8 Although the prevalence is probably very low,
familial cerebral cavernous vascular malformations predominate in
Hispanics in the southwestern United States.9 10
Native Americans constitute
The available cardiovascular data on Native Americans
from various parts of the United States, mainly from the National
Health and Nutrition Examination Survey I and II, suggest that they may
have a higher prevalence of diabetes mellitus, tobacco smoking, and
obesity than whites.13 Additional well-documented
cardiovascular risk factor information, including
alcoholism and drug abuse, in well-defined homogeneous
Native American populations is needed to optimize vascular disease
prevention efforts.
The best way to study differences between ethnic or racial groups is to
investigate community populations by using standardized
diagnostic criteria and verified diagnoses. Hospital-based
studies are prone to patient selection bias. Patients referred to a
given medical center are selected on the basis of their health
insurance coverage, a specific disorder in which the receiving medical
center specializes, the interest and confidence with which the
referring physicians treat patients with similar disorders, presence of
other complicating diseases, and proximity to the medical center. A
large proportion of patients with similar disorders, living in the same
community, are probably not referred to the study center unless it is
the only medical facility for a given community. This is beyond the
control of the investigators. Because of this unavoidable bias, results
from a hospital-based study may or may not apply to the same groups of
people living in the community. For example, in the study published in
this issue of the journal,14 the proportion of stroke
patients with intracerebral hemorrhage is
unusually high among whites (37%) and Hispanics (48%). The expected
proportion of intracerebral hemorrhages among
whites is 10%, based on various other stroke registries. The
proportion of strokes due to intracerebral
hemorrhage among Hispanics has not been studied in a
southwestern US community population, but in New York City it was
11%.8 This is one reason why the subjects in this study
are unlikely to be a representative sample of stroke
patients in the community.
Another possible source of confusion from epidemiological studies is
when results are based solely on diagnostic codes or death
certificates. These documents are completed by a variety of people
without specific standardized guidelines. In some instances, the
diagnosis of stroke may be questionable or key diagnostic
tests may be missing. This could lead to coding inaccuracies. In
instances in which the cause of death is unconfirmed, the designation
may be based on the presence of risk factors and other available
clinical information. The accuracy of such determinations is likely to
be low. Consequently, the accuracy of these medical documents are
variable, and the results based on them may be erroneous. Review of
pertinent medical records with standardized and reasonably strict
criteria to confirm the diagnoses will minimize errors.
Only community-based studies, with proper standardized definitions and
verified diagnoses of the disorders being investigated, will
convincingly answer the important questions regarding vascular
differences between various ethnic and racial groups. In addition, to
maximize the chances of demonstrating differences between ethnic and
racial groups, if they exist, each group should be defined to make it
as homogeneous as is reasonably possible. Ancestry,
environment, and culture should be similar within each group.
Footnotes
The opinions expressed in this editorial are not necessarily those of the editors or of the American Heart Association.
Reviews of this manuscript were directed by Hermes Kontos, MD, and Marie-Germaine Bousser, MD. Because of possible conflict of interest, Drs Mark Dyken and José Biller were not involved in the reviews.
References
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Caplan LR. Strokes in
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Gorelick P, Caplan L, Langenberg P, Hier D, Pessin M,
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asymptomatic occlusive cerebrovascular disease.
Neurology.. 1988;38:852-858.
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Inzitari D, Hachinski VC, Taylor DW, Barnett HJ.
Racial differences in the anterior circulation in
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factors? Arch Neurol.. 1990;47:1080-1084.
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Wityk R, Lehman D, Klag M, Coresh J, Ahn H, Litt B.
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Gillum RF. Epidemiology
of stroke in Hispanic Americans. Stroke.. 1995;26:1707-1712.
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Bruno A, Carter S, Qualls C, Nolte KB.
Incidence of spontaneous intracerebral
hemorrhage among Hispanics and non-Hispanic whites in New
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Bruno A, Carter S, Qualls C, Nolte KB.
Incidence of spontaneous subarachnoid hemorrhage
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Sacco RL, Hauser WA, Mohr JP. Hospitalized
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Kattapong VJ, Hart BL, Davis LE. Familial
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Knowler WC, Pettitt DJ, Saad MF, Bennett PH.
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Mitchell B, Stern M. Recent developments in the
epidemiology of diabetes in the
Americas. World Health Stat Q.. 1992;45:347-349.[Medline]
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Gillum RF. The
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Americans. Stroke.. 1995;26:514-521.
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© 1998 American Heart Association, Inc.
Editorial
Are There Differences in Vascular Disease Between Ethnic and Racial Groups?
Key Words: genetics • racial differences • stroke • ethnic groups • vascular diseases
9.0% of the US population according to the
1990 US census, and a large majority of them live in the southwestern
United States. The ancestors of the Hispanics in the southwestern
United States are mainly the settlers and conquerors who came from
Spain starting in the 16th century. Since their arrival in the southern
part of North America, there has been cultural and genetic interaction
between the Spanish and the various Native American tribes living in
this region. The Hispanics who relatively recently immigrated from
Mexico to the southwestern United States have a similar ancestry. 0.8% of the US population according to
the 1990 US census. The Native Americans came to the Americas from Asia
tens of thousands of years ago, when the Bering Straights area was land
connecting the two continents. Before the arrival of Europeans in the
Americas, Native Americans had already spread over the continents and
developed a variety of cultures influenced by various ecological
conditions. In the southwestern United States, Native Americans have
been divided into four groups, the Yuma, Pima-Papago, Pueblo, and
Apache. These groups probably are exposed to different vascular risks
and have different attitudes toward health and illness. These
differences are likely to influence the extent of detection and control
of vascular risks. Since the arrival of Europeans in the Americas,
cultural and genetic integration with Native Americans has been
occurring to some degree. Some Native Americans live on reservations,
but most live in neighboring communities and periodically visit their
native reservation. Consequently, Native Americans in the southwestern
United States are heterogeneous people. An example of a
physiological difference between the Native
American tribes in the southwestern United States is the unusually high
prevalence of diabetes mellitus among the Pima Indians of
Arizona.11 12 Studying a combination of Native American
groups may mask differences between them.
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