Alzheimer’s May Have A Different Trajectory for Women
Biological difference may explain why women have higher AD risk
By Judy George, Contributing Writer for MedPage Today
Women developed more tau pathology than men with similar amyloid burden, an analysis of cross-sectional data found.
Across two cohorts of older cognitively normal adults, women with higher amyloid burden showed higher entorhinal cortical tau compared with men with higher amyloid burden, reported Reisa Sperling, MD, of Brigham and Women’s Hospital and Massachusetts General Hospital, both in Boston, and colleagues, in JAMA Neurology.
“In the current study, the sex difference was most apparent in the entorhinal cortex, where tangles are accumulating as we age and then begin to spread throughout the cortex as memory impairment becomes manifest,” she added. “These findings may be important in targeting appropriate prevention therapies for women, ideally preventing the accumulation of both amyloid and tau pathology as early as possible.”
Alzheimer’s dementia is more common in women than men, and women are more likely to show Alzheimer’s disease pathophysiology. Among apolipoprotein E (APOE) ε4 carriers — both clinically normal older adults and those with mild cognitive impairment — women exhibited higher levels of cerebrospinal fluid (CSF) tau levels than men. Last year, a meta-analysis found greater CSF total and phosphorylated tau in female APOE ε4 carriers, with findings driven by abnormal levels of amyloid-beta.
Sex differences in amyloid burden alone have not been reported in older adults. This may suggest that male-female differences appear downstream, after amyloid beta starts to accumulate, Sperling and colleagues observed.
To study this, they evaluated two cross-sectional convenience samples of clinically normal individuals who received both tau and amyloid beta PET scans from January 2016 to February 2018. The Harvard Aging Brain Study (HABS) cohort included 193 clinically normal individuals (ages 55-92; 61% women) who had carbon 11–labeled Pittsburgh Compound B (PIB) PET to assess amyloid beta. The Alzheimer’s Disease Neuroimaging Initiative (ADNI) cohort had 103 clinically normal individuals (ages 63-94; 51% women) who underwent florbetapir PET to assess amyloid beta.
Among amyloid-positive individuals, women had more tau signal in their entorhinal cortices than men (meta-analytic estimate of beta for males -0.11, 95% CI -0.21 to -0.02, P=0.02).
That gap grew wider with increased amyloid: with higher amyloid-beta burden, women showed higher entorhinal cortex tau than men in both the HABS (beta -0.17, 95% CI -0.32 to -0.01, P=0.04) and the ADNI (beta -0.23, 95% CI -0.42 to -0.04, P=0.02) cohorts.
In the HABS group, sex and APOE did not appear to interact to influence tau deposits. In the ADNI group, a sex-by-APOE ε4 interaction was found in a meta-region that included the entorhinal cortex, inferior temporal cortex, amygdala, fusiform gyrus, and the parahippocampal cortex, with the association between APOE ε4 and tau retention stronger among women than men.
This study builds on previous research “suggesting sex differences, albeit very subtle, in Alzheimer’s pathology,” noted Michelle Mielke, PhD, of the Mayo Clinic in Rochester, Minnesota, who was not involved with the study.
The study had several limitations. The analysis was based on convenience samples; recruitment and sampling biases may result affect findings. The ADNI group was older, showed lower memory performance, and may have been further along the preclinical Alzheimer’s trajectory. The cohorts also differed in how amyloid-beta was assessed. Limitations with power and neuropsychological follow-up in this study mean results should be approached with caution, the authors stated.
“Although our findings are consistent across two large cohorts, the sex differences in tau levels are relatively small, and there are likely other factors contributing to cognitive decline that we need to study,” Sperling said. “We are also working on longitudinal tau PET imaging studies to determine if women have faster rates of tau accumulation over time that may correlate with the rates of memory decline.”