adpd-2026-precision-medicine-genetic-stratification

AD/PD 2026: Precision Medicine and Genetic Stratification

Dates: March 17-21, 2026 Location: Copenhagen, Denmark Organizer: Kenes Group

Overview

Precision medicine — tailoring diagnosis, prevention, and treatment to individual genetic profiles — has transitioned from theoretical aspiration to clinical reality at AD/PD 2026. The conference showcased how genetic stratification is reshaping clinical trial design, enabling targeted therapies, and guiding diagnostic pathways for both Alzheimer's disease and Parkinson's disease[@bellenguez2022][@correia2023].

The field has matured beyond single-gene associations toward polygenic risk scores that integrate dozens to hundreds of genetic variants, and beyond pharmacogenetics toward mechanistic stratification that links genetic risk to specific biological pathways. For AD, APOE4 remains the central risk factor with new understanding of its mechanistic role in tau pathology. For PD, LRRK2 and GBA represent the most actionable genetic targets, with multiple disease-modifying therapies in development specifically for these populations.

Alzheimer's Disease Genetic Stratification

APOE4: The Central AD Risk Factor

APOE4 Homozygosity as a Distinct Disease Form

One of the most significant conceptual advances presented at AD/PD 2026 was the reframing of APOE4 homozygosity not merely as a risk factor but as a distinct genetic form of Alzheimer's disease[@chen2023]. Key evidence supporting this reclassification:

AD/PD 2026: Precision Medicine and Genetic Stratification

Dates: March 17-21, 2026 Location: Copenhagen, Denmark Organizer: Kenes Group

Overview

Precision medicine — tailoring diagnosis, prevention, and treatment to individual genetic profiles — has transitioned from theoretical aspiration to clinical reality at AD/PD 2026. The conference showcased how genetic stratification is reshaping clinical trial design, enabling targeted therapies, and guiding diagnostic pathways for both Alzheimer's disease and Parkinson's disease[@bellenguez2022][@correia2023].

The field has matured beyond single-gene associations toward polygenic risk scores that integrate dozens to hundreds of genetic variants, and beyond pharmacogenetics toward mechanistic stratification that links genetic risk to specific biological pathways. For AD, APOE4 remains the central risk factor with new understanding of its mechanistic role in tau pathology. For PD, LRRK2 and GBA represent the most actionable genetic targets, with multiple disease-modifying therapies in development specifically for these populations.

Alzheimer's Disease Genetic Stratification

APOE4: The Central AD Risk Factor

APOE4 Homozygosity as a Distinct Disease Form

One of the most significant conceptual advances presented at AD/PD 2026 was the reframing of APOE4 homozygosity not merely as a risk factor but as a distinct genetic form of Alzheimer's disease[@chen2023]. Key evidence supporting this reclassification:

• Penetrance: Nearly 100% of APOE4/4 homozygotes develop AD pathology by age 85, approaching monogenic disease penetrance
• Pathological mechanisms: Distinct from amyloid-driven AD, with APOE4/4 showing accelerated tau pathology independent of amyloid burden
• Treatment response: Differential response to anti-amyloid therapies (lower lecanemab efficacy, higher ARIA risk in APOE4/4)
• Biomarker trajectory: Accelerated amyloid accumulation, earlier tau PET positivity, more rapid neurodegeneration

APOE Allele Distribution and AD Risk

| Genotype | Relative Risk vs. E3/E3 | Lifetime Risk (Women) | Lifetime Risk (Men) |
|----------|------------------------|----------------------|---------------------|
| E2/E2 | 0.4x (protective) | ~5% | ~3% |
| E2/E3 | 0.6x (protective) | ~10% | ~7% |
| E3/E3 | Reference (1x) | ~15% | ~10% |
| E3/E4 | 2-3x elevated | ~25-30% | ~15-20% |
| E4/E4 | 12-15x elevated | ~55-60% | ~35-40% |

The dose-dependent effect of APOE4 reflects its semi-dominant inheritance pattern, with heterozygotes showing intermediate risk[@genin2011].

Clinical Implications of APOE Testing

APOE genotyping in clinical practice:

• Diagnostic utility: Supports AD probability assessment in symptomatic patients
• Risk communication: Enables discussion of lifetime risk, though requires careful counseling
• Treatment selection: Critical for anti-amyloid therapy decision-making (ARIA risk stratification)
• Clinical trial stratification: Essential for trial design, particularly for prevention studies

• Lecanemab: APOE4/4 carriers show 30-40% less amyloid reduction vs. non-carriers
• ARIA risk: APOE4/4 increases ARIA-E incidence 3-4 fold, ARIA-H 2-fold compared to E3/E3
• Dosing considerations: Some protocols recommend reduced dosing for E4 homozygotes
• Monitoring: More frequent MRI monitoring warranted in E4/4 patients

Polygenic Risk Scores for AD

Development and Validation

Polygenic risk scores (PRS) aggregate the effects of hundreds to thousands of genetic variants associated with AD risk, providing continuous risk stratification that complements single-gene testing[@truchardet2023].

AD PRS construction:

• GWAS variants: 100-500+ variants from large-scale AD GWAS (predominantly European-ancestry)
• Effect size weighting: Each variant weighted by its association strength (beta coefficient)
• Ancestral portability: PRS developed in one population requires recalibration for others
• Performance: PRS explains 7-15% of phenotypic variance, with top quintile showing 3-4x increased risk vs. bottom quintile

• Trans-ancestry PRS developed using African, Asian, and Hispanic ancestry cohorts
• Performance maintained across populations after recalibration
• Critical need for continued expansion of non-European GWAS samples

• PRS in combination with blood biomarkers (p-tau217) achieved AUC >0.95 for AD
• PRS provides independent information from fluid biomarkers
• Combined model enables risk prediction 10-15 years before symptoms

• PRS-enriched prevention trials demonstrate feasibility
• Top PRS quintile allows smaller sample sizes for equivalent power
• Ongoing debate about ethical implications of genetic enrichment

Clinical Implementation Challenges

Monogenic and Early-Onset AD

APP, PSEN1, and PSEN2 Mutations

Early-onset autosomal dominant Alzheimer's disease (ADAD) is caused by mutations in [APP](/genes/app), [PSEN1](/genes/psen1), and [PSEN2](/genes/psen2). These rare variants provide mechanistic insight applicable to sporadic AD.

PSEN1 mutations (most common):

• Over 300 pathogenic variants identified
• Age of onset typically 30-60 years
• Mechanisms: increased Aβ42 production, altered Aβ42/Aβ40 ratio
• Genotype-phenotype correlations being refined

• Phenocopy of Down syndrome-associated AD (APP triplication)
• Typical onset 40-55 years
• Associated with cerebral amyloid angiopathy

• Rarer than PSEN1
• Later onset than PSEN1 (typically 50-70 years)
• Some variants show reduced penetrance

• PSEN1 mutation carriers show highly predictable amyloid accumulation rates
• Aβ42/40 ratio in CSF may help differentiate PSEN1 from PSEN2
• Treatment responses in ADAD cohorts inform sporadic AD treatment development
• DIAN-TU and other prevention trials continue to refine intervention windows[@simons2024]

ABCA7 and Other Moderate-Risk Genes

Beyond APOE, several genes confer moderate AD risk (odds ratios 1.2-2.0):

| Gene | Function | Risk Effect | Mechanism |
|------|----------|-------------|-----------|
| ABCA7 | Lipid transport | OR ~1.2-1.3 | Amyloid processing, phagocytosis |
| CLU (Apolipoprotein J) | Complement regulation | OR ~1.1-1.2 | Amyloid clearance, inflammation |
| PICALM | Synaptic vesicle trafficking | OR ~1.1 | Endocytosis, synaptic function |
| BIN1 | Membrane trafficking | OR ~1.1-1.2 | Tau pathophysiology |
| SORL1 | Retromer function | OR ~1.2-1.5 | APP trafficking, amyloid production |
| TREM2 | Microglial activation | OR ~2-3 (loss-of-function) | Amyloid clearance, inflammation[@zhan2023] |

TREM2 variants:
Loss-of-function TREM2 variants (including R47H) confer approximately 3-fold increased AD risk[@zhan2023]. The variant impairs microglial transition to disease-associated states, reducing amyloid clearance capacity. This has direct therapeutic implications — TREM2-activating antibodies (e.g., AL002) are in clinical development specifically for TREM2 variant carriers.

Parkinson's Disease Genetic Stratification

LRRK2: The Most Common PD Genetic Form

G2019S and Other Pathogenic Variants

LRRK2 mutations are the most common genetic cause of Parkinson's disease, accounting for 1-5% of sporadic PD and up to 40% of familial PD in certain populations (particularly those of North African Arab and Ashkenazi Jewish ancestry)[@correia2023].

G2019S (Gly2019Ser):

• Most common LRRK2 variant (5-6% of familial PD)
• Located in the kinase domain — results in increased kinase activity
• Autosomal dominant inheritance with age-dependent penetrance (~30% by age 80)
• Phenotype generally resembles idiopathic PD with typical motor features
• Good response to dopaminergic therapy
• Reduced non-motor symptoms compared to idiopathic PD in some cohorts

• N1437H, R1441C/G/H, Y1699C — all in ROC domain
• Variable penetrance and phenotypic expression
• Similar kinase hyperactivity mechanism

LRRK2 as a Therapeutic Target

LRRK2 has emerged as one of the most tractable therapeutic targets in PD, with multiple disease-modifying therapies in development:

Kinase inhibitors:

• DNL151 / BIIB094 (Denali): LRRK2 inhibitor, Phase 2 completed — demonstrated target engagement and good safety profile
• DNL343 (Denali): CNS-penetrant LRRK2 inhibitor, earlier-stage development
• JM10 (Neuroscience): Brain-penetrant LRRK2 inhibitor in early clinical testing

• Lysosomal function (LAMP2A, GBA interaction)
• Primary cilia function (implicated in dopamine neuron survival)
• Synaptic vesicle trafficking
• Neuroinflammation via microglial effects

• DNL151 showed sustained target engagement at doses used in Phase 2
• Biomarker evidence of reduced neurodegeneration markers in LRRK2 inhibitor-treated patients
• Next-generation inhibitors with improved brain penetration advancing
• Patient selection strategies: LRRK2 variant carriers show greatest treatment response

GBA: The Most Prevalent PD Genetic Risk Factor

GBA1 Variants and PD Risk

Heterozygous [GBA](/genes/gba) variants represent the most common genetic risk factor for Parkinson's disease, present in 5-15% of PD patients depending on ancestry[@sidransny2020].

Pathogenic GBA variants:

• N370S, L444P, E326K, N408S (rs356182)
• Complex alleles (recombinations, recombinant haplotypes)
• Variant-specific penetrance and phenotype

• N370S: OR ~5-7 for PD development
• L444P: OR ~8-10 (associated with more severe phenotype)
• E326K: OR ~2-3 (lower penetrance, more prevalent)
• Population frequency varies by ancestry (highest in Ashkenazi Jewish: 15-20% carrier rate)

• Earlier onset (average 5-7 years earlier than non-carriers)
• More rapid progression
• Higher prevalence of cognitive impairment and dementia (up to 30%)
• More prominent non-motor features (autonomic dysfunction, REM sleep behavior disorder)
• Greater tau pathology burden on PET imaging

GBA as a Therapeutic Target

Mechanism-based approach:
GBA variants reduce glucocerebrosidase enzyme activity, leading to:

• Accumulation of glucocerebroside (GluCer) in lysosomes
• Impaired lysosomal protein degradation
• Alpha-synuclein accumulation (feedback loop)
• Mitochondrial dysfunction
• Endoplasmic reticulum stress

• Ambroxol: Acidic beta-glucosidase (GCase) chaperone, increases GBA activity
• Venglustat (GZ/SAR402671): GBA substrate reduction therapy
• AD/PD 2026: Ambroxol trials showed increased GCase activity and reduced alpha-synuclein in CSF

• Prevents accumulation of toxic glucocerebroside metabolites
• Multiple programs in clinical development

• AAV-GBA delivery for sustained expression
• Preclinical promise, early clinical planning

• Phase 2 ambroxol trials: 20-30% increase in GCase activity in CSF, trend toward clinical stabilization
• Venglustat: Phase 2 data showed biomarker effects but limited clinical benefit in initial readout
• Next-generation chaperones with improved CNS penetration in development

SNCA: Alpha-Suclein Gene Variants

Point mutations and duplications:

• SNCA A53T (most common pathogenic point mutation)
• SNCA triplication — gene dose correlates with severity and earlier onset
• A30P, E46K, H50Q, G51D — rare variants with variable penetrance
• PD phenotype with prominent autonomic and cognitive features

• RBD prevalence higher in SNCA mutation carriers
• Hyposmia and constipation may precede motor symptoms by years
• SAA positivity can be detected in prodromal SNCA carriers

Polygenic Risk for PD

PD PRS development:
Recent GWAS have identified >90 independent risk loci for Parkinson's disease, enabling construction of polygenic risk scores[@singh2024].

PRS applications:

• Risk stratification in prodromal populations
• Clinical trial enrichment
• Understanding genetic architecture of PD subtypes
• Integration with environmental risk factors

• PRS composed of 90+ variants explains ~7-8% of phenotypic variance
• Top PRS decile shows 2.5-3x increased PD risk vs. bottom decile
• PRS combined with environmental risk factors (pesticides, head trauma) improves prediction
• Trans-ancestry PRS development ongoing to address European bias

Genetic Testing in Clinical Practice

Indications for genetic testing in PD:

Genetic testing panels:

• PD panel: LRRK2, GBA, SNCA, PARK2 (parkin), PINK1, DJ1, VPS35, ATP13A2
• AD panel: APOE, PSEN1, PSEN2, APP, ABCA7, TREM2, SORL1
• Next-generation sequencing: Whole exome or targeted panels are standard approach

• Penetrance variability complicates risk communication
• Limited therapeutic options for positive results in some cases
• Insurance and employment discrimination concerns
• Family implications of cascade testing

Cross-Disease Genetic Overlap

Shared Genetic Architecture

AD and PD share some genetic risk factors, reflecting common cellular vulnerability pathways:

| Gene | AD Effect | PD Effect | Shared Mechanism |
|------|-----------|-----------|------------------|
| SNCA | Weak | Strong | Alpha-synuclein aggregation |
| MAPT | Weak | Moderate | Tau pathology, microtubule dynamics |
| HLA region | Moderate | Moderate | Immune regulation, microglial function |
| CLU | Moderate | Weak | Complement, inflammation |
| TREM2 | Moderate | Weak | Microglial activation |
| GBA | Weak | Strong (via lysosomal) | Lysosomal function, alpha-synuclein |

Multi-Morbidity and Mixed Pathology

Genetic risk profiling increasingly recognizes that many patients have overlapping pathology:

• APOE4 carriers with PD show more rapid cognitive decline
• GBA carriers show more tau PET burden than non-carriers
• Combined amyloid + synuclein pathology detectable via SAA panels

Precision Medicine Implementation

Biomarker-Guided Stratification Framework

The integration of genetic risk with fluid biomarkers creates a powerful stratification framework:

Clinical Trial Enrichment

Genetic stratification is transforming clinical trial design:

Genotype-specific trials:

• LRRK2 inhibitor trials: Require LRRK2 G2019S or other pathogenic variants
• GBA chaperone trials: Require heterozygous GBA variant
• TREM2 agonist trials: Require TREM2 loss-of-function variant (R47H)

• APOE4/4: Separate trials for anti-amyloid therapy response
• Early-onset AD: Different endpoints, shorter timelines
• Prodromal carriers: Prevention trial designs

• Genotype-matched baskets across diseases (e.g., LRRK2 inhibitors for PD and Crohn's disease)
• Platform trials with molecular eligibility criteria

Challenges in Precision Implementation

Future Directions

Near-Term Developments (2026-2028)

Longer-Term Vision (2028-2032)

Cross-References

• [AD/PD 2026 Blood Biomarkers](/biomarkers/adpd-2026-blood-biomarkers)
• [AD/PD 2026 Seed Amplification Assays](/biomarkers/adpd-2026-seed-amplification-assays)
• [Combination Biomarker Panels for Alzheimer's Disease](/biomarkers/combination-biomarker-panels-ad)
• [LRRK2 Gene](/genes/lrrk2)
• [GBA Gene](/genes/gba)
• [SNCA Gene](/genes/snca)
• [APOE Gene](/entities/apoe)
• [Alzheimer's Disease Biomarkers](/biomarkers/alzheimers-disease-biomarkers)
• [Parkinson's Disease Biomarkers](/biomarkers/parkinsons-disease-biomarkers)
• [AD/PD 2026 Conference](/events/adpd-2026)
• [AD/PD 2026 Clinical Trial Updates](/events/adpd-2026-clinical-trials)
• [AD/PD 2026 Emerging Therapeutic Targets](/events/adpd-2026-emerging-therapeutic-targets)
• [MDS 2026 Genetics and Biomarkers in Movement Disorders](/biomarkers/mds-2026-genetics-biomarkers-movement-disorders)