Differences among the three ethnoracial groups were found for nearly all study variables. In particular, the Latino group had younger age at onset of AD, more cognitive impairment and dementia at the time of initial presentation, and more depressive symptoms. African Americans had a slightly older age of onset than WNHs, but levels of dementia severity and cognitive impairment were intermediate between WNHs and Latinos. Also of interest is the apparent absence of apolipoprotein E e4 genotype as a risk factor for AD in our Latino cohort.
Many sociocultural factors contribute to general health and limit access to healthcare and could delay evaluation, which might skew the clinical profile at initial presentation. We considered if this delay contributed to differences in severity. We found no statistically significant differences between any of the groups in the interval between first onset of symptoms and evaluation in our ADC. This suggests that in this population, perhaps due to effective outreach and recruitment, there is equivalent access. Other studies explain greater symptom severity as being related to a lack of linguistically and culturally appropriate care providers.32
It is also possible that differences in how members of different ethnoracial groups recognize cognitive decline and assign a time of onset could be responsible for delays in evaluation, thus explaining the greater severity of symptoms at first visit. In a study in which Latinos and WNHs were queried about their understanding of the cause of AD both groups reported “genes” as a major cause; however, Latinos were more likely to report “stress” as a cause, whereas WNHs reported an idea about “plaques” or “brain plasticity.”33
Support for the hypothesis that lower education is associated with higher levels of cognitive impairment, increased risk of dementia, and more rapid cognitive decline is mixed, particularly when other variables including pathophysiology of the disease and symptom severity are taken into consideration.30,34
In our sample, there were considerable differences in education between the groups, especially notable for low education levels in many Latinos. Education is considered a proxy for many factors (eg, poverty, nutrition, healthcare access) that affect health as well as the expression of disease, particularly cognitive disorders. We attempted to control for education statistically by using years of education as a regressor in statistical analyses. Although these adjustments attenuated the ethnoracial differences, significant associations between ethnoracial group and cognition persisted. In some comparisons however (eg, Latinos versus WNHs for global cognition), statistical adjustment for education eliminated the ethnoracial group effect, even when the difference between groups was extremely large.
Another variable often associated with functional decline and poorer cognitive performance is depression.25,35,36
Greater endorsement of depressive symptoms by Latinos in both AD and NCI groups could reflect higher distress levels in this largely poor, linguistically and culturally isolated immigrant group. Alternatively, it could indicate a culturally specific reflection of disease expression or a different degree of endogenous mood symptoms. Our data highlight the need to better understand how depression contributes to or is associated with cognitive impairment.
Finally, this study found even stronger evidence than the North Manhattan project12
that APOE-e4 is not as highly associated with AD diagnosis in Caribbean Latinos as it is in African Americans and WNHs. In our study population, there was no association of APOE-e4 genotype with AD diagnosis or cognition in the Latino cohort, while this association was strong in the African American and WNH groups. Furthermore, and in contrast to recently reported findings,37
we found no difference in age of onset in Latino APOE e4 carriers than noncarriers, unlike WNH or African American groups.
Normative data are lacking for language-translated study measures, posing a challenge to ADCs serving diverse communities in the United States.38
This allows for potential confounds related to cultural bias and inadequate reference groups. One way to assess the contributions of cultural bias in the present study was to look for potential differences between the performances of people in different ethnoracial groups with NCI. For instance, we observed strong differences among the groups in the Boston naming task and digit symbol substitution task, but not the clock draw or 10-item word list learning and recall tests. Future studies using measures less susceptible to cultural bias will be important. Other studies have found that even when demographic variables such as age, education, gender and socioeconomic background are held constant disparities remain in scores on commonly used neuropsychological testing measures.39
There are important limitations to acknowledge in this study. As a descriptive study using a convenience sample, it cannot draw causal inferences about the variables under consideration and the onset and progression of dementia. Furthermore, the nature of our sample, which likely includes a degree of self-selection bias, may preclude generalization to the general population. Also, the Latino community in the United States is very diverse and our cohort principally included people of Puerto Rican heritage, resident of a culturally secluded and economical deprived area of Philadelphia. Therefore, caution must be heeded when attempting to generalize data from this study to other Latino communities or even other immigrant or nonimmigrant Puerto Rican communities. Furthermore, selection into ethnoracial group was determined by self-report. It can be argued that these classifications are socially constructed classifications and therefore subjective. Finally, the Latino individuals included in this study represent a fairly restricted range of education and socioeconomic level. The especially low levels of education reported by the Latino members of this cohort are noteworthy as a significant confound. They are also mostly immigrants and have had the added stress of relocation and acculturation. Finally, the recruitment methods for many of the Latino and African American participants involved targeted outreach efforts that were different from the way in which we recruited the WNH subjects into the cohort. The African American and Latino participants were approached in a primary care health clinic in North Philadelphia or screened through other outreach endeavors at the West Philadelphia Primary Care office. Furthermore, studies comparing immigrant and nonimmigrant Latino communities will be important to identify the contributions of these many factors.