Alzheimer’s Disease Duration and Outcome Vary According to Ethnoracial Groups, Study Finds

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by Patricia Inacio, PhD |

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Hispanic-American patients with Alzheimer’s disease tend to live significantly longer after disease onset and with milder cognitive decline than African-Americans and non-Hispanic whites, a study reports.

The study, “Ethnoracial differences in Alzheimer’s disease from the FLorida Autopsied Multi-Ethnic (FLAME) cohort,” was published in the journal Alzheimer’s & Dementia.

Epidemiological data supports a higher incidence of Alzheimer’s disease in the United States among Hispanic and African-Americans compared with non-Hispanic white individuals. Despite this, Hispanics with Alzheimer’s live longer than blacks and Caucasians, a phenomenon known as the “Hispanic mortality paradox.

The neurological and genetic factors that may underlie these differences remain unknown, so Mayo Clinic researchers sought to examine the demographic and clinical differences across these three ethnoracial groups of Alzheimer’s patients from the FLAME study.

“This study utilized one of the largest series of donated brain tissue to date, looking at demographic and clinicopathologic features of Alzheimer’s disease across an ethnoracially diverse group of cases,” Melissa Murray, PhD, a Mayo Clinic translational neuropathologist and the study’s lead author said in a press release.

The team analyzed 1,625 brain tissue samples from patients who died and had self-identified as Hispanic (67 patients), African-American (19 patients), and non-Hispanic white (1,539 patients). Within the Hispanic group, most patients were of Caribbean origin, mainly from Cuba and Puerto Rico, while a few were of Mexican, Central or South American origin.

Hispanic-American patients were more likely to have a family history of dementia, and disease onset was a year or more earlier — at the age of 70 — than the other groups. They had lower cognitive scores at the end of life compared with the other ethnoracial groups, as measured using the Mini-Mental State Examination (MMSE) test.

Despite all these characteristics, Hispanic-American patients lived longer with the disease — 12 years — compared with nine years for non-Hispanic whites and eight years for African-Americans.

Researchers then evaluated differences in tangle formation (the abnormal twisting of cellular filaments that hold neurons in their proper shape), which is a hallmark of Alzheimer’s disease. They found subtle differences between the three ethnoracial groups but no differences were found for brain weight after adjusting for sex, age at onset, or disease duration.

Hispanic-Americans were less likely to carry a genetic variant known to increase the risk of Alzheimer’s, called APOE 4, although this difference was not statistically significant compared with other groups.

The presence of additional neurodegenerative disorders, specifically TDP-43 hippocampal sclerosis — characterized by the loss of neurons in a brain region called the hippocampus — was 5.4 times higher in African-Americans compared with the non-Hispanic whites after adjusting for sex, age at onset, and disease duration.

No significant differences in education level and employment rates — considered to have protective effects against cognitive decline — were seen between the three groups.

“Hispanic and African-American populations tend to be underrepresented in Alzheimer’s research, despite having 1½ to two times the risk of getting the disease, compared to non-Hispanic white Americans,” Murray said.

“Our hope is that our findings will help Hispanic- and African-Americans overcome the historical and cultural barriers that contribute to their reluctance to participate in research. Our findings of longevity may have important implications in terms of addressing disparities in caregiver needs, social and family impact, and cost of care,” she added.

In future studies, the researchers intend to explore the factors — such as family support and potential protective proteins — that may underlie the longer survival of Hispanic-American patients.