GWAS Findings Hub: Alzheimer's and Parkinson's Disease

GWAS Findings Hub: Alzheimer's and Parkinson's Disease

Introduction

Genome-wide association studies (GWAS) have revolutionized our understanding of the genetic architecture of neurodegenerative diseases. Unlike rare causative mutations that cause familial forms, GWAS identifies common genetic variants with modest effect sizes that influence disease risk, age at onset, and progression. This hub synthesizes major GWAS findings for Alzheimer's disease (AD) and Parkinson's disease (PD), mapping risk loci to biological pathways and therapeutic targets.

Methodology Overview

GWAS Findings Hub: Alzheimer's and Parkinson's Disease

Introduction

Genome-wide association studies (GWAS) have revolutionized our understanding of the genetic architecture of neurodegenerative diseases. Unlike rare causative mutations that cause familial forms, GWAS identifies common genetic variants with modest effect sizes that influence disease risk, age at onset, and progression. This hub synthesizes major GWAS findings for Alzheimer's disease (AD) and Parkinson's disease (PD), mapping risk loci to biological pathways and therapeutic targets.

Methodology Overview

GWAS for neurodegenerative diseases employ case-control designs with increasingly large cohorts. The International Genomics of Alzheimer's Project (IGAP) and Parkinson's Disease Genetics Consortium (PDGC) have identified dozens of risk loci through meta-analyses of tens of thousands of cases and controls.

Key methodological considerations:

• Sample sizes: Early GWAS (2009-2013) used ~10,000 subjects; modern studies exceed 100,000
• Imputation: Use of reference panels (HRC, 1000 Genomes) enables coverage of rare variants
• Heritability: SNP heritability (h² SNP) estimates suggest 20-30% of disease variance is captured by common variants
• Pleiotropy: Many loci affect multiple neurodegenerative diseases, revealing shared mechanisms

[Alzheimer's Disease](/diseases/alzheimers-disease) GWAS

Major Risk Loci

| Gene/Region | Chromosome | Odds Ratio | Pathway | Function |
|-------------|------------|------------|---------|----------|
| [APOE](/genes/apoe) | 19q13.32 | 3.5-4.0 (ε4) | Lipid metabolism, Aβ clearance | Cholesterol transport, amyloid binding |
| [TREM2](/genes/trem2) | 6p21.1 | 2.6-4.5 | Neuroinflammation, microglia | Triggering receptor on myeloid cells |
| [BIN1](/genes/bin1) | 2q14.3 | 1.2-1.3 | Synaptic function, endocytosis | Bridging integrator 1, tau biology |
| [CLU](/genes/clu) | 8p21.1 | 1.1-1.2 | Protein homeostasis | Clusterin, complement regulation |
| [PICALM](/genes/picalm) | 10q24.3 | 1.1-1.2 | Endocytosis, autophagy | Phosphatidylinositol binding |
| [CR1](/genes/cr1) | 1q32.1 | 1.1-1.2 | Neuroinflammation | Complement receptor 1 |
| [CD33](/genes/cd33) | 19q13.41 | 1.1-1.2 | Neuroinflammation | Sialic acid receptor on microglia |
| [ABCA7](/genes/abca7) | 19p13.3 | 1.1-1.2 | Lipid metabolism | ATP-binding cassette transporter |
| [PTK2B](/genes/ptk2b) | 8p21.2 | 1.1 | Synaptic plasticity | Protein tyrosine kinase |
| [SORL1](/genes/sorl1) | 11q24.1 | 1.1-1.3 | APP processing | Sortilin-related receptor |
| [MEF2C](/genes/mef2c) | 5q14.3 | 1.1 | Synaptic plasticity | Myocyte enhancer factor 2C |
| [NME8](/genes/nme8) | 7p31.3 | 1.1 | Axonal function | NM23-H8, sphingolipid metabolism |
| [RIN3](/genes/rin3) | 14q32.12 | 1.1 | Endocytosis | Ras and Rab interactor 3 |
| [INPP5D](/genes/inpp5d) | 2q37.1 | 1.1 | Neuroinflammation | SHIP1, microglial signaling |
| MADD/SPI1 | 11p11.2 | 1.1 | Apoptosis, microglia | SPI1 regulates microglial genes |

Pathway Analysis

AD GWAS loci converge on several key biological pathways:

1. Lipid Metabolism and Cholesterol Transport

• [APOE](/genes/apoe), [ABCA7](/genes/abca7), [CLU](/genes/clu) participate in lipid homeostasis
• Dyslipidemia is a known AD risk factor
• [APOE](/genes/apoe) ε4 carriers have impaired [Aβ](/proteins/amyloid-beta) clearance
• See: [APOE Lipid Pathway](/mechanisms/apoe4-alzheimers)

• TREM2, CR1, CD33, INPP5D, SPI1 regulate microglial function
• TREM2 variants affect amyloid plaque clearance
• Chronic neuroinflammation drives tau pathology
• See: TREM2 Microglia Pathway, [Neuroinflammation in AD](/mechanisms/neuroinflammation)

• BIN1, PICALM, RIN3 are involved in endocytosis
• Endolysosomal dysfunction is an early AD feature
• Synaptic loss correlates with cognitive decline

• SORL1 regulates APP trafficking
• Genetic variants affect Aβ production
• See: APP Amyloid Pathway

GWAS Summary Statistics

Recent meta-analyses (IGAP 2019) identified 29 risk loci explaining ~7.7% of SNP heritability. Remaining heritability may reside in rare variants detectable only through sequencing studies.

[Parkinson's Disease](/diseases/parkinsons-disease) GWAS

Major Risk Loci

| Gene/Region | Chromosome | Odds Ratio | Pathway | Function |
|-------------|------------|------------|---------|----------|
| GBA | 1q21 | 2.0-5.0 | Lysosomal function | Glucocerebrosidase, α-syn clearance |
| SNCA | 4q21 | 1.3-1.5 | Protein aggregation | α-synuclein, Lewy body formation |
| LRRK2 | 12q12 | 1.3-2.0 | Protein kinase signaling | Leucine-rich repeat kinase 2 |
| MAPT | 17q21.31 | 1.2-1.4 | Cytoskeleton, tau | Microtubule-associated protein tau |
| PARK16 | 1q32 | 1.3 | Endoplasmic reticulum | ER stress, lipid metabolism |
| BST1 | 4p15 | 1.2 | Calcium signaling | Bone stromal cell antigen |
| SNCA (repeat) | 4q21 | 1.4-1.8 | α-syn propagation | Multiplication leads to PD |
| GCH1 | 14q22 | 1.2 | Dopamine synthesis | GTP cyclohydrolase 1 |
| DR2 (Parkinson) | 11q13 | 1.2 | Dopamine signaling | Dopamine receptor D2 |
| VPS35 | 16q11 | 1.5-2.0 | Endosomal trafficking | Vacuolar protein sorting 35 |
| DNAJC13 | 3q22 | 1.3 | Endosomal function | Co-chaperone |
| OR4K2 | 5q33 | 1.2 | Olfactory function | May relate to olfactory loss |
| CCDC62 | 5q35 | 1.2 | Vesicle trafficking | HIV-1 interaction protein |
| STX1B | 16p12 | 1.1 | Synaptic transmission | Syntaxin 1B |
| FAM47E | 4p14 | 1.1 | Unknown | Function unclear |

Pathway Analysis

PD GWAS reveals distinct mechanistic clusters:

1. Lysosomal and Autophagy Pathways

• GBA variants are the strongest genetic risk factor
• Reduced glucocerebrosidase activity impairs α-syn clearance
• ATP13A9 (PARK9) also lysosomal
• See: Autophagy-Lysosome Pathway

• SNCA locus quadruplication causes parkinsonism
• Risk variants may affect expression
• See: Alpha-Synuclein Aggregation Pathway

• PINK1, PRKN (PARK2) are recessive mitochondrial genes
• mtDNA variants contribute to risk
• See: Mitochondrial Dysfunction in PD

• LRRK2 affects microglial activation
• Genetic overlap with inflammatory diseases

• GCH1, TH affect tyrosine hydroxylase
• Links to levodopa response

GWAS Summary Statistics

PD GWAS (Nalls et al. 2019, 2014) identified 90+ risk loci explaining ~16-22% of SNP heritability. Unlike AD, PD shows strong monogenic forms (LRRK2, SNCA, GBA) that inform biological pathways.

Shared Genetics: Cross-Disease Pathways

Several genetic loci and pathways are shared between AD and PD:

1. Neuroinflammation

• TREM2 (AD) ~ microglial activation
• LRRK2 (PD) ~ microglial signaling
• INPP5D common to both

• APOE (AD major risk)
• GBA affects lipid composition in lysosomes
• ABCA7 in both

• PICALM, BIN1 (AD)
• VPS35, DNAJC13 (PD)
• Shared endocytic trafficking dysfunction

• SNCA (PD Lewy bodies)
• tau (MAPT) in both PD and AD
• See: Protein Aggregation Comparison

Therapeutic Implications

Target Identification

GWAS findings directly inform drug development:

| GWAS Target | Therapeutic Approach | Status |
|-------------|---------------------|--------|
| TREM2 | Agonist antibodies (AL002) | Phase 2 for AD |
| APOE | Gene therapy, apoE mimetics | Preclinical |
| LRRK2 | Inhibitors (DNL151, BIIB122) | Phase 2 for PD |
| GBA | Substrate reduction therapy | Phase 2 for PD |
| SNCA | Immunotherapy (prasinezumab) | Phase 2 for PD |
| BIN1 | Tau-targeting | Preclinical |

Polygenic Risk Scores

GWAS enables polygenic risk scores (PRS) that:

• Stratify individuals by genetic risk
• Identify high-risk populations for prevention trials
• May predict age at onset
• Guide personalized prevention strategies

Database Resources

• IGAP: International Genomics of Alzheimer's Project
• PD Genetics Consortium: International PD GWAS meta-analyses
• GWAS Catalog: NIH database of all GWAS findings
• PD Gene: Comprehensive PD genetics database
• AlzGene: AD genetics database (archived)

See Also

• [APOE Lipid Pathway](/mechanisms/dopaminergic-neuron-vulnerability)
• [TREM2 Microglia Pathway](/mechanisms/trem2-microglia-pathway-alzheimers)
• [Neuroinflammation in AD](/mechanisms/neuroinflammation)
• [APP Amyloid Pathway](/mechanisms/app-amyloid-pathway-alzheimers)
• [Autophagy](/entities/autophagy)
• [Alpha-Synuclein Aggregation Pathway](/mechanisms/alpha-synuclein-pathology)
• [Mitochondrial Dysfunction in PD](/mechanisms/pd-mitochondrial-dysfunction)
• [Protein Aggregation Comparison](/mechanisms/dopaminergic-neuron-vulnerability)
• [Lysosomal Dysfunction in Neurodegeneration](/mechanisms/lysosomal-dysfunction)
• [Neuroinflammation in AD and PD](/mechanisms/dopaminergic-neuron-vulnerability)

External Links

• [PubMed](https://pubmed.ncbi.nlm.nih.gov/)
• [KEGG Pathways](https://www.genome.jp/kegg/pathway.html)

Related Pages

• [Genetics of Neurodegenerative Diseases](/mechanisms/genetics)
• [Alzheimer's Disease Genetic Variants](/diseases/alzheimers-genetic-variants)
• [Parkinson's Disease Genetic Variants](/diseases/parkinsons-genetic-variants)
• [TREM2 Microglia Pathway](/mechanisms/trem2-microglia-pathway-alzheimers)
• [Alpha](/mechanisms/alpha-synuclein-aggregation)
• [APOE Lipid Pathway](/mechanisms/dopaminergic-neuron-vulnerability)
• [Lysosomal Dysfunction in Neurodegeneration](/mechanisms/lysosomal-dysfunction)
• [Neuroinflammation in AD and PD](/mechanisms/dopaminergic-neuron-vulnerability)

References