African-American and European-American Brains Affected Differently by Alzheimer’s

Alzheimer’s disease may cause different changes in the brain, or pathologies, in African-Americans than in white Americans of European descent, according to a study published in the July 15, 2015, online issue of Neurology.

“Because some studies suggest that Alzheimer’s disease is more common among older African-Americans than European-Americans, we wanted to see whether the brain changes caused by Alzheimer’s are different in these two racial groups,” said study author Lisa L. Barnes, PhD, with Rush University Medical Center in Chicago. “Studying how Alzheimer’s disease looks in the brain in individuals of different races may help us to further understand the disease and pinpoint strategies for prevention and treatment.”

The study included 41 African-Americans with a clinical diagnosis of Alzheimer’s dementia from the memory clinic, who had an autopsy of their brain performed after death. They were then compared to 81 deceased European-Americans who had Alzheimer’s dementia with the same level of disease severity and were of the same age, sex and education level. Researchers looked for typical signs of Alzheimer’s disease (plaques and tangles) as well as other brain changes that can cause dementia, such as infarcts (the brain changes associated with stroke) and Lewy bodies (associated with Lewy body or Parkinson’disease). They noted whether people had just one pathology or more than one. They also looked at small and large blood vessel disease.

Almost all participants in the study had Alzheimer’s disease in their brain. Only about half of the European-Americans had pure Alzheimer’s disease pathology (no additional pathologies contributing to dementia) whereas the rest had Alzheimer’s disease pathology with either infarcts or Lewy bodies. In contrast, less than 25 percent of the African Americans had pure Alzheimer’s disease pathology. On the other hand, almost three-quarters (71 percent) of African-Americans had Alzheimer’s disease pathology mixed with another type of pathology, compared to 51 percent of European-Americans. Clinical Alzheimer’s disease in African-Americans was much more likely to involve pathologies other than Alzheimer’s disease pathology. African-Americans also had more frequent and severe blood vessel disease.

This image is a labeled diagram of an alzheimer's brain slice.
Almost all participants in the study had Alzheimer’s disease in their brain. Only about half of the European-Americans had pure Alzheimer’s disease pathology (no additional pathologies contributing to dementia) whereas the rest had Alzheimer’s disease pathology with either infarcts or Lewy bodies. Image is for illustrative purposes only.

“Our study has important clinical implications because it may suggest a need for different types of Alzheimer’s prevention and treatments in African-Americans. Indeed, current Alzheimer’s drugs primarily target specific Alzheimer pathologies in the brain. Given the mixed pattern of disease that we see in African American brains, it will be important to develop new treatments that target these other common pathologies, particularly for African-Americans,” said Barnes.

About this neurology research

Funding: The study was supported by the National Institutes of Health and the Illinois Department of Public Health.

Source: Rachel Seroka – AAN
Image Credit: The image is in the public domain
Original Research: Abstract for “Cognitive impairment 18 years before clinical diagnosis of Alzheimer disease dementia” by Kumar B. Rajan, Robert S. Wilson, Jennifer Weuve, Lisa L. Barnes, and Denis A. Evans in Neurology. Published online June 24 2015 doi:10.1212/WNL.0000000000001774


Abstract

Cognitive impairment 18 years before clinical diagnosis of Alzheimer disease dementia

Objective: To examine the relation of performance on brief cognitive tests to development of clinically diagnosed Alzheimer disease (AD) dementia over the following 18 years in a sample of African Americans and European Americans.

Methods: A composite cognitive test score based on tests of episodic memory, executive function, and global cognition was constructed in a prospective population-based sample of 2,125 participants (55% African American and 61% female) aged 65 years and older residing in 4 Chicago neighborhoods. Time before AD dementia diagnosis was categorized into 6 groups corresponding to data collection periods: 0.1–0.9, 1.0–3.9, 4.0–6.9, 7.0–9.9, 10.0–12.9, and 13.0–17.9 years.

Results: Of 2,125 participants without clinical AD dementia, 442 (21%) developed clinical AD dementia over 18 years of follow-up. Lower composite cognitive test scores were associated with the development of AD dementia over the duration of the study. The magnitude of association between composite cognitive test score and development of AD dementia increased from an odds ratio of 3.39 (95% confidence interval 1.72, 6.67; p < 0.001) at 13.0–17.9 years to 9.84 (95% confidence interval 7.41, 13.06; p < 0.001) at 0.1–0.9 years, per SD increment. These associations were consistently larger among European Americans than among African Americans. Performance on individual cognitive tests of episodic memory, executive function, and global cognition also significantly predicted the development of AD dementia, with associations exhibiting a similar trend over 18 years. Conclusions: Our findings suggest that cognitive impairment may manifest in the preclinical phase of AD dementia substantially earlier than previously established.

“Cognitive impairment 18 years before clinical diagnosis of Alzheimer disease dementia” by Kumar B. Rajan, Robert S. Wilson, Jennifer Weuve, Lisa L. Barnes, and Denis A. Evans in Neurology. Published online June 24 2015 doi:10.1212/WNL.0000000000001774

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