Research agenda for understanding Alzheimer disease in diverse populations: work group on cultural diversity, Alzheimer's association

Challenging Assumptions About African American Participation in Alzheimer Disease Trials

OBJECTIVE

The authors investigated potential effects of increased African American participation in Alzheimer disease (AD) and mild cognitive impairment (MCI) clinical trials by examining differences in comorbid conditions and treatment outcome affecting trial design.

METHODS

Using a meta-database of 18 studies from the Alzheimer's Disease Cooperative Study and the Alzheimer's Disease Neuroimaging Initiative, a cohort of 5,164 subjects were included for whom there were baseline demographic data and information on comorbid disorders, grouped by organ system. Meta-analysis was used to compare prevalence of comorbidities, dropouts, and rates of change on the cognitive subscale of the Alzheimer's Disease Assessment Scale by race. Clinical trial scenarios similar to recent therapeutic trials were simulated to determine effects of increased African American participation on statistical power.

RESULTS

Approximately 7% of AD, 4% of MCI, and 11% of normal participants were African American. African American subjects had higher prevalence of cardiovascular disorders (odds ratio: 2.10; 95% confidence interval [CI]: 1.71-2.57) and higher rate of dropouts (odds ratio: 1.60; 95% CI: 1.15-2.21) compared with whites but lower rates of other disorders. There were no significant differences in rate of progression (-0.862 points/year; 95% CI: -1.89 to 0.162) by race and little effect on power in simulated trials with sample sizes similar to current AD trial designs.

CONCLUSION

Increasing African American participation in AD clinical trials will require adaptation of trial protocols to address comorbidities and dropouts. However, increased diversity is unlikely to negatively affect trial outcomes and should be encouraged to promote generalizability of trial results.

Differences in the frequency of Alzheimer's disease-associated genomic variations in populations of different races

AIM

The general genetic background is important when studying major common diseases, such as Alzheimer's disease (AD). Determining the underlying genetic factors in populations of different races might allow for the tailored management of such diseases. The aim of the present study was to identify potential single-nucleotide polymorphisms (SNP) and genes associated with racial differences.

METHODS

We identified AD-associated SNP with different carrier frequencies among races through the National Human Genome Research Institute and 1000 Genome Project databases. We generated heatmaps and carried out principle component analysis and pathway analysis. A total of 99 AD-associated SNP from genome-wide association studies were found to have different frequencies among races. Principle component analysis showed that specific SNP had higher or lower frequencies in specific races, and that similar races were clustered together.

RESULTS

Pathway analysis showed that a total of 15 pathways involving intracellular endocytosis, inflammation, immune response and lipid metabolism were significant, and that apolipoprotein E was involved in the most significant pathways. A literature review showed that 16 genes were involved in the pathogenesis of AD, and that the identified SNP could be used to cluster different races, suggesting that these SNP represented different genomic backgrounds of races.

CONCLUSIONS

As disease-associated genes might have several functional variants across different populations, these genes could be candidates for further studies, such as target gene sequencing or functional follow up of putative loci regarding racial differences. Geriatr Gerontol Int 2017; 17: 2184-2193.

The Role of Ethnicity in Alzheimer's Disease: Findings From The C-PATH Online Data Repository

BACKGROUND

Ethnic minorities seem to be at an increased risk of Alzheimer's disease (AD). However, little is known about ethnic differences and the risks of early onset AD (EOAD).

OBJECTIVE

Cognitive function changes over time and odds of EOAD by ethnicity were analyzed by the mixed model and the logistic regression.

METHODS

Information on demographics, self-reported co-morbidities, cognitive functions (MMSE and ADAS-COG), and ApoE genotypes were collected for 6,500 subjects with AD obtained from the placebo arm of clinical trials; this data was examined by ethnicities: Caucasian, Asian, African American, Hispanic, and other minorities--including Native Alaskans, Americans, and Hawaiians.

RESULTS

Of the total subjects, Caucasians accounted for 89.0% , followed by 4.7% Asians, 2.7% African Americans, 2.4% Hispanics, and 1.2% Native Americans, Alaskans, and Hawaiians. Age, gender, EOAD status, co-morbidities, family history of AD, and ApoE genotypes were significantly different by ethnicity. ApoE ɛ2 allele is possibly overrepresented in the Native Americans, Africans, Hawaiians, and African Americans. A significant interaction with time, ethnicity, and cognitive performance was found, indicating more cognitive deterioration in other minorities than Caucasians for mini-mental state (p <  0.01). After adjusting for co-morbidities and gender, the odds of EOAD among African Americans (OR: 1.6, 95% CI: 1.1-2.4) and Native Alaskans, Americans, and Hispanics (OR: 2.1, 95% CI: 1.2-3.5) were significantly higher, compared with Caucasians.

CONCLUSIONS

Ethnicity may impact AD through age of onset, co-morbidities, family history, ApoE gene status, and cognitive change over time. The greater odds of EOAD among African Americans, Alaskans, and Hawaiians suggest that some ethnicities may be at risk of AD at a younger age.

Perspective on race and ethnicity in Alzheimer's disease research

There are adequate scientific, public health, and ethical justifications for studying Alzheimer's disease (AD) in persons of varying race and ethnicity, but to be meaningful variables, race and ethnicity must be examined in context. The complex interactions between race, ethnicity, lifestyle, and environmental factors, such as climate and diet, require that future studies of AD in specific racial or ethnic groups attend to measures of racial/ethnic homogeneity and the assessment of the environment and the elements that comprise the ethnicity of groups under study. Instead of arbitrarily selecting specific racial or ethnic groups in the hope of finding important differences, it may be in the long run less costly and more efficient to recruit families with highly positive (or negative) family histories, to search within these groups for possible racial or ethnic differences, and to investigate the possible racial or ethnic reasons for those differences.

Culturally attuned recruitment, retention, and adherence in Alzheimer disease and associated disorders: a best practices working model

This analysis presents a recruitment, retention, and (treatment and/or research) adherence (RRA) best practices model for targeting Alzheimer disease and associated dementias (ADAD) impacting ethnically diverse populations. RRA practice involves many more factors beyond cultural considerations to be highlighted here. However, it is the cultural dimension where much is at stake, where there is the least comprehensive framework, and where the most ambiguity exists relative to RRA practice. The discussion proceeds on three premises. First, a composite, culturally attuned RRA working model can be assembled from the current literature. Second, culturally speaking, recruitment, retention, and adherence are essentially linked processes. Although each of the components of RRA practice has its own unique set of tasks, culture permeates them all. Third, any RRA practice model that emerges must be tailored to the communities, the specific target populations, and the programmatic circumstances to which the effort is attached.

Black-white disparities in functional decline in older persons: the role of cognitive function

BACKGROUND

Black elders have a greater frequency of functional decline than do white elders. The impact of cognitive function on explaining black-white disparities in functional decline has not been extensively explored.

METHODS

To compare the extent to which different risk domains (comorbidity, smoking, socioeconomic status (SES), self-rated health, and cognitive function) explain more frequent functional decline in black elders, we studied 779 black and 4892 white community-dwelling adults aged 70 and older from the Assets and Health Dynamics Among the Oldest Old (AHEAD), a population-based cohort study begun in 1993. Our primary outcome was worse functional status at 2 years than at baseline. We used logistic regression to compare the unadjusted with the adjusted black-white odds ratios (ORs) after adjusting for each risk domain.

RESULTS

At baseline black participants aged 70-79 had higher rates of smoking, diabetes, and hypertension; lower SES; and worse cognitive function than did white participants (p <.05 for all). The mean cognitive score was 15.7 in black and 21.8 in white participants (p <.01). Black participants had a higher frequency of 2-year functional decline than did white participants (10.9% vs 4.7%; OR = 2.61, 95% confidence interval [CI], 1.69-4.03 adjusted for age and sex). Adjustment for comorbidity and smoking did not significantly change the black-white OR, whereas self-rated health and SES accounted for about half the risk. Adjustment for cognitive function accounted for nearly all the associated decline (OR = 1.10, 95% CI, 0.67-1.79). Among participants aged 80 and over, those who were black had significantly lower risk for functional decline after adjustment for cognitive function (OR = 0.61, 95% CI, 0.38-0.96 vs OR = 1.08, 95% CI, 0.70-1.66 adjusted for age and sex only).

CONCLUSIONS

Cognitive function mediated the higher frequency of functional decline among black elders. Efforts to understand cognitive function may enhance our understanding of black-white disparities in health outcomes.