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Original Investigation
January 7, 2019

Assessment of Racial Disparities in Biomarkers for Alzheimer Disease

Author Affiliations
  • 1Department of Neurology, Washington University School of Medicine, St Louis, Missouri
  • 2Knight Alzheimer Disease Research Center, Washington University School of Medicine, St Louis, Missouri
  • 3Division of Biostatistics, Washington University School of Medicine, St Louis, Missouri
  • 4Department of Radiology, Washington University School of Medicine, St Louis, Missouri
  • 5Department of Psychiatry, Washington University School of Medicine, St Louis, Missouri
JAMA Neurol. Published online January 7, 2019. doi:10.1001/jamaneurol.2018.4249
Key Points

Question  Do African American individuals differ from non-Hispanic white individuals regarding molecular biomarkers of Alzheimer disease?

Findings  This cohort study of 1255 participants in a study of healthy aging and Alzheimer disease found significant differences in the cerebrospinal fluid concentrations of tau protein (and its phosphorylated isoform) between African American and white individuals.

Meaning  Racial differences in Alzheimer biomarkers suggest possible race-dependent biological mechanisms that contribute to expression of disease.

Abstract

Importance  Racial differences in molecular biomarkers for Alzheimer disease may suggest race-dependent biological mechanisms.

Objective  To ascertain whether there are racial disparities in molecular biomarkers for Alzheimer disease.

Design, Setting, and Participants  A total of 1255 participants (173 African Americans) were enrolled from January 1, 2004, through December 31, 2015, in longitudinal studies at the Knight Alzheimer Disease Research Center at Washington University and completed a magnetic resonance imaging study of the brain and/or positron emission tomography of the brain with Pittsburgh compound B (radioligand for aggregated amyloid-β) and/or cerebrospinal fluid (CSF) assays for the concentrations of amyloid-β42, total tau, and phosphorylated tau181. Independent cross-sectional analyses were conducted from April 22, 2016, to August 27, 2018, for each biomarker modality with an analysis of variance or analysis of covariance including age, sex, educational level, race, apolipoprotein E (APOE) ε4 allele status, and clinical status (normal cognition or dementia). All biomarker assessments were conducted without knowledge of the clinical status of the participants.

Main Outcomes and Measures  The primary outcomes were hippocampal volumes adjusted for differences in intracranial volumes, global cerebral amyloid burden as transformed into standardized uptake value ratios (partial volume corrected), and CSF concentrations of amyloid-β42, total tau, and phosphorylated tau181.

Results  Of the 1255 participants (707 women and 548 men; mean [SD] age, 70.8 [9.9] years), 116 of 173 African American participants (67.1%) and 724 of 1082 non-Hispanic white participants (66.9%) had normal cognition. There were no racial differences in the frequency of cerebral ischemic lesions noted on results of brain magnetic resonance imaging, mean cortical standardized uptake value ratios for Pittsburgh compound B, or for amyloid-β42 concentrations in CSF. However, in individuals with a reported family history of dementia, mean (SE) total hippocampal volumes were lower for African American participants than for white participants (6418.26 [138.97] vs 6990.50 [44.10] mm3). Mean (SE) CSF concentrations of total tau were lower in African American participants than in white participants (293.65 [34.61] vs 443.28 [18.20] pg/mL; P < .001), as were mean (SE) concentrations of phosphorylated tau181 (53.18 [4.91] vs 70.73 [2.46] pg/mL; P < .001). There was a significant race by APOE ε4 interaction for both CSF total tau and phosphorylated tau181 such that only APOE ε4–positive participants showed the racial differences.

Conclusions and Relevance  The results of this study suggest that analyses of molecular biomarkers of Alzheimer disease should adjust for race. The lower CSF concentrations of total tau and phosphorylated tau181 in African American individuals appear to reflect a significant race by APOE ε4 interaction, suggesting a differential effect of this Alzheimer risk variant in African American individuals compared with white individuals.

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