Alzheimer's disease research has long centered on APOE-ε4 as the dominant genetic risk factor, yet that lens was calibrated almost entirely on European-ancestry populations. For the tens of millions of older African Americans — a group that faces disproportionately high Alzheimer's risk — a different genetic variant may be doing far more neurological damage, and far earlier than structural imaging would reveal.
In a cohort of 146 older African Americans (mean age ~70), carriers of the ABCA7 rs115550680 risk allele showed measurably lower medial temporal lobe (MTL) network flexibility compared to both non-carriers and APOE-ε4 carriers — a statistically significant difference that held after controlling for age, sex, education, and APOE-ε4 status. MTL flexibility, derived from resting-state fMRI, quantifies how dynamically the brain reconfigures functional connectivity over time — a metric increasingly recognized as sensitive to early neurodegenerative disruption before structural atrophy appears. Additionally, ABCA7 rs115550680 carriers displayed paradoxical hypertrophy in the left anterior hippocampus and bilateral entorhinal cortex, a pattern consistent with compensatory neuroinflammatory or glial responses documented in early-stage AD pathology.
This finding carries significant implications for how Alzheimer's risk stratification is conducted across ancestral populations. ABCA7, a lipid transporter gene, has known roles in amyloid precursor processing and microglial phagocytosis — pathways mechanistically distinct from the apolipoprotein-driven cascade linked to APOE-ε4. The observation that functional network disruption precedes measurable volume loss in this cohort aligns with a growing body of evidence that dynamic connectivity metrics may outperform structural MRI as early biomarkers. Key limitations include the modest sample size, cross-sectional design preventing causal inference, and the absence of amyloid or tau biomarker confirmation. Still, this is among the first studies to directly compare these two genetic variants on functional brain outcomes in an African American sample — an incremental but clinically meaningful step toward ancestry-specific Alzheimer's risk modeling.