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An international study combining genetic data from 30 cohorts identified 127 Alzheimer’s disease risk loci, including 48 not previously reported. The researchers also found that estimates of genetic contribution varied by analytical method; the findings do not establish that genes account for a specific new share of individual risk or prove that proposed drug targets work.
An international study drawing on genetic data from nearly 2.8 million people identified 127 genetic loci associated with Alzheimer’s disease, including 48 not previously reported, and found that estimates of genetic contribution can differ with the method used. The findings point to immune-cell and neuronal biology as areas linked to inherited risk, but they do not show that genes cause a newly quantified share of Alzheimer’s cases or that the suggested drug targets are effective treatments.
The study, published in Nature under the title “Alzheimer’s disease genetics converges on microglial and neuronal dysregulation,” combined summary data from 30 cohorts. The dataset included 109,479 people with Alzheimer’s, 74,141 proxy cases, 2,131,799 controls and 499,708 proxy controls. Proxy cases were people who reported that a parent had Alzheimer’s or dementia; they did not have Alzheimer’s themselves in that analysis. The researchers reported an effective sample size of 416,493.
The team found 118 significant loci in its multi-ancestry analysis and nine more in an analysis limited to European ancestry, for 127 overall. The 48 newly identified loci add to evidence about the biological pathways associated with Alzheimer’s. The study also identified 72 significant gene sets, with results clustering around lipid binding, immune activation, amyloid breakdown and cell adhesion.
Analyses linked Alzheimer’s genetic associations to genes expressed in microglia, immune cells in the brain, and to several neuronal populations. The microglial association remained significant after the researchers adjusted for average differences in gene expression across cell types. Neuronal associations became only nominally significant after adjustment, and the authors said it remains uncertain whether those expression differences contribute to disease or result from neurodegeneration.
The researchers also highlighted five potential drug targets: RRM2B, SYK, KEAP1, CACNA1S and AXL. These were candidates identified through genetic and other analyses, not medicines tested in this study. The report notes that earlier research had mixed results for some targets, including no improved outcomes in cited studies involving CACNA1S and AXL.
What the New Loci Add
The findings broaden the genetic map researchers can use to investigate how Alzheimer’s develops. Associations involving microglial immune activity, lipid processes and neuronal biology may help direct further work toward mechanisms beyond the amyloid-beta aggregates targeted by current disease-modifying treatments. The genetic results do not, by themselves, establish that changing any one pathway will prevent or treat the disease.
The work also revisits a gap between estimates of inherited susceptibility and estimates based on common genetic variants. Twin studies have put Alzheimer’s susceptibility heritability at 60% to 80%, while earlier single-nucleotide-polymorphism estimates cited by the study suggested common variants accounted for about 5% of disease liability. The researchers examined whether analytical approaches contributed to that difference. Heritability estimates describe variation in a population, not the probability that a particular person will develop Alzheimer’s.
More complete genetic evidence could eventually support better risk research and help identify biological targets for drug development. But the study does not establish a clinical test, change individual risk estimates, or demonstrate that the proposed targets can improve patient outcomes.
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How the Genetic Estimates Differ
Alzheimer’s disease is the most common form of dementia. The study’s background notes that dementia from all causes is projected to affect 153 million people worldwide by 2050. Earlier genome-wide association studies had identified about 80 Alzheimer’s risk loci, while twin studies and analyses of common variants produced notably different estimates of inherited contribution.
To assess genetic associations, the researchers analyzed ancestry groups separately and combined results using a fixed-effect meta-analysis. They also estimated SNP-based heritability with SBayesRC and compared it with estimates from linkage disequilibrium score regression. Simulations using UK Biobank data examined how differences between methods might affect heritability estimates. The supplied report does not give a single revised percentage that can replace the earlier estimate.
The study included participants grouped by European, African, East Asian, admixed American and South Asian ancestry. However, about 91% of the effective sample was of European ancestry. The researchers said results for ancestry groups with smaller samples were less precise, limiting how confidently the findings can be applied across populations.
“The analyses identified 118 significant loci in the multi-ancestry analysis and nine additional loci in the European-ancestry-only analysis, giving 127 loci overall; 48 were newly identified.”
— The study authors, as summarized in the supplied report
Limits on Risk and Treatment Claims
The study’s results do not settle what proportion of Alzheimer’s risk is genetic. The supplied report says the investigators compared heritability methods and used simulations, but does not provide a definitive revised percentage. Heritability estimates also concern population-level differences and cannot be read as an individual’s personal risk.
It is also unclear whether the gene-expression patterns found in neurons are part of the disease process or a consequence of degeneration. The inflammatory microglial pattern had the strongest association, but no individual microglial state reached statistical significance, according to the report.
The five proposed drug targets were not tested as treatments in this study. The data therefore do not show that targeting them would prevent Alzheimer’s, slow its progression or improve symptoms. The ancestry imbalance and reduced precision in smaller groups also leave uncertainty about how well the findings apply across populations.
Further Tests of Genetic Findings
The next steps are to replicate the associations, study how the implicated genes affect brain cells, and test whether the proposed biological targets have effects in laboratory and clinical research. Larger and more balanced genetic datasets could improve the precision of findings for ancestry groups that were less represented in this analysis.
Researchers would also need to clarify how different heritability methods produce their estimates and what those estimates mean for Alzheimer’s biology. Any future treatment claim would require separate testing for safety and benefit; the genetic associations reported here are a starting point for that work, not evidence of a ready-to-use therapy.
Key Questions
What did the Alzheimer’s genetics study find?
It identified 127 genetic loci associated with Alzheimer’s, 48 of them newly reported, using data from 30 cohorts. It also found associations involving microglial and neuronal biology.
Does the study prove genes account for more Alzheimer’s risk than previously thought?
No. The researchers examined how methods affect estimates of genetic contribution, but the supplied report does not state a definitive new percentage. The findings should not be treated as an individual risk calculation.
Are the five highlighted genes proven Alzheimer’s drug targets?
No. RRM2B, SYK, KEAP1, CACNA1S and AXL were highlighted as potential targets through the study’s analyses. They were not tested as treatments in this research.
How representative was the study across ancestry groups?
The analysis included five ancestry groupings, but about 91% of the effective sample was of European ancestry. The report says results in groups with smaller samples were less precise.
Source: news-medical.net
