Gene-Environment Interactions in Dementia and Alzheimer's Disease: A Multidimensional Roadmap

Authors: Basma M. Saleh and Mohamed Salama Institution: IGHHE, The American University in Cairo

1. Introduction: The "Missing Heritability" Problem

• Beyond Static Genetics: GWAS identifies many risk loci, but genetics alone do not explain Alzheimer’s incidence → strong role for Gene-Environment interactions.

• Exposome Concept: Totality of environmental and social exposures (diet, pollution, education) modifies genetic risk across lifespan.

• Consensus: 57% of analyzed literature agrees environmental/social factors significantly modulate dementia risk.

2. Methods: PRISMA Systematic Search

• Identification: 221,500 papers initially screened across Consensus, Publited, Semantic Scholar.

• Filtering: Narrowed to 228 screened → 157 eligible studies.

• Final Inclusion: 50 high-quality papers (systematic reviews, GWAS, PRS, MR studies).

3. Key Findings

Ancestral Diversity

• ABCA7 → higher risk in African Americans.

• APOE c4 → attenuated impact in some African populations.

Biological Pathways

• Loci: BIN1, PICALM.

• Pathways disrupted: neuroinflammation, lipid metabolism, endocytosis, amyloid/tau processing.

Environmental Modifiers

• Air pollution (PM2.5/NOx).

• Mediterranean diet adherence.

• Sleep disruption (REM/NREM).

• Cognitive reserve (years of schooling).

Epigenetic Mediators

• DNA methylation & histone acetylation act as molecular switches.

• Genes turned on/off in response to stress or toxins without DNA sequence change.

4. Methodological Frontiers

• MAGEE & Statistical Frameworks: Detect subtle GxE effects, handle non-linear exposures.

• GxE-informed Polygenic Risk Scores (PRS): Move beyond additive models → weight variants by environmental interactions for better prediction.

5. Research Gaps & Future Directions

• Eurocentric Bias:

  • GWAS loci: 15 in European cohorts vs 4 in African cohorts.

  • PRS validation: 10 European vs 2 African cohorts.

• Toward Precision Prevention:

  • Tailored interventions (e.g., air filtration for pollution-sensitive genotypes).

  • Move beyond universal advice.

• Research Gap Matrix: Visualizes lack of diversity in GxE research.

6. Conclusion

• Central Role of GxE: Integrating environmental monitoring + diverse ancestral data is cornerstone of dementia prevention by 2030.

• Precision Needed: “Precision in measuring the exposome must match genomic precision.”

• Equity Goal: Closing gap between environmental tracking and genetic data is essential for global brain health.

Contact: Basma_saleh@aucegypt.edu