Alzheimer's traits may vary across races

A new study has revealed that the changes and pathologies associated with Alzheimer's disease may vary depending on race.

Scientists have discovered the effect of Alzheimer's disease may vary depending on race.

The findings, published in the Neurology, compared the neurological disorder in white Americans of European descent and African-Americans, and there proved to be a striking contrast.

Pure Alzheimer's disease, in which no additional pathologies contribute to dementia, was most common in European-Americans. 

Forty-two (42%) percent of Alzheimer's cases among European-Americans fell into this category, compared with just 19.5% of African-Americans. 

However, the latter were more likely to have the disease with another type of pathology.

As the average life expectancy around the world increases, so does the risk of Alzheimer's disease. The disease typically affects seniors and is the most common type of dementia - an estimated 5.3 million Americans are diagnosed with Alzheimer's.

The disease is a classified as a neurological disorder that affects the brain, causing the destruction of cells and affecting one's cognitive ability. Although scientists and doctors cannot test the living brain for Alzheimer's disease, a postmortem or autopsy will always show tiny inclusions in the nerve tissue called plaques and tangles that are symptomatic of the disease.

Plaques are located between dying cells and are created by the build-up of a protein called beta-amyloid. Tangles are found within brain neurons and are created from the disintegration of another protein, called tau.

Important clinical implications

Studies have previously shown that African-Americans are more prone to the disease. This revelation prompted the researchers from the Rush University Medical Center in Chicago, IL, to investigate further.

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 a total of 122 individuals - 41 African-Americans and 81 European-Americans. Each African-American individual was matched at a ratio of 2 to 1 with a European-American of the same level of disease severity. An effort was also made to ensure age, sex and education matched between the two groups.

Researchers looked for 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 (which are associated with Lewy body or Parkinson's disease).

Almost all patients displayed signs of Alzheimer's disease in their brains. However, the researchers discovered that only 19.5% of African-Americans in the study had Alzheimer's as a single dementia pathology, compared with 42% of European-Americans.

Instead, 71% of African-Americans were found to have Alzheimer's disease mixed with another type of pathology. A figure higher than their European-American counterparts, where the figure was 51%. In addition, African-Americans were found to have more frequent and severe blood vessel disease.

Dr. Barnes believes the results of the study have "important clinical implications" for the prevention and treatment of Alzheimer's. She explains:

Current Alzheimer's drugs primarily target specific Alzheimer's pathology in the brain. Given the mixed pattern of the disease that we see in the brains of African-American people, it will be important to develop new treatments that target these other common pathologies, particularly for African-Americans.

The dangers in generalizing results from one population to another

Although the sample in the study represented the largest to date, she admitted more numbers were required, especially regarding African-Americans:

We need to do a better job of raising awareness in the African-American community of the opportunities to participate in studies. Community-based strategies where researchers engage and educate communities about the symptoms of Alzheimer's, the importance of research, and the benefits of participation will help to recruit greater numbers in clinical trials.

At the moment, there are few brain studies on minority populations, but as the total number of American seniors increases, so will the proportion of older Americans in different racial and ethnic groups. 

As the numbers of ethnic and racial minorities increase in the oldest age groups, Alzheimer's and other neurodegenerative diseases will place a disproportionate burden on minorities.

"Almost everything we have learned about Alzheimer's has been learned on predominantly white populations because they are the 'typical' research participant. The current study underscores the dangers of generalizing results from one population to another population."

Researchers are still striving for a cure for the disease. Among the top 10 causes of death, Alzheimer's is the only disease for which scientists have yet to find a way to prevent, stop or slow its progression.

References:

1.  Mixed pathology is more likely in black than white decedents with Alzheimer dementia, Lisa Barnes et al., Neurology, doi: 10.1212/WNL.0000000000001834, published online 15 July 2015, abstract.
2.  Additional Source: Alzheimer's Association, 2015 Alzheimer's disease facts and figures, accessed 13 July 2015.