Document Code: SCF-AMC-STRANDSHIFT-GSEA-0001
Program: PROJECT STRANDSHIFT
Classification: Repeat Expansion Origin & Progression Atlas
Primary Focus: HTT CAG Repeat Dynamics Across Germline Transmission and Somatic Evolution
1. EXECUTIVE SUMMARY
The Germline vs Somatic Expansion Atlas defines the two fundamental expansion processes responsible for Huntington disease pathogenesis:
Germline Expansion
Expansion occurring during reproductive transmission from parent to offspring.
Responsible for:
- Disease inheritance
- Intergenerational anticipation
- Earlier age of onset in descendants
Somatic Expansion
Expansion occurring within tissues during an individual’s lifetime.
Responsible for:
- Progressive neuronal toxicity
- Regional brain vulnerability
- Disease progression
- Clinical severity
Core STRANDSHIFT Hypothesis
Huntington disease is initiated through germline transmission but amplified through somatic genomic evolution.
Disease Burden:
Inherited Mutation+Lifetime Somatic Expansion
Clinical Phenotype
2. MASTER EXPANSION FRAMEWORK
Expansion Architecture
Layer 1
Germline Expansion
↓
Layer 2
Inherited HTT Genotype
↓
Layer 3
Somatic Expansion
↓
Layer 4
Cellular Toxicity
↓
Layer 5
Neurodegeneration
↓
Layer 6
Clinical Disease
3. GERMLINE EXPANSION ATLAS
Definition
Change in HTT CAG repeat length during transmission between generations.
Primary Biological Source
Spermatogenesis
Highest instability.
Oogenesis
Lower instability.
4. PATERNAL EXPANSION PATHWAY
Characteristics
- Greater repeat instability
- Larger expansion events
- Increased anticipation
- Higher juvenile HD risk
Mechanistic Drivers
DNA Replication Slippage
Mismatch Repair Activity
Germ Cell Division Frequency
Repeat Loop Formation
Outcome
Parent
45 CAG
↓
Child
60 CAG
↓
Earlier Disease Onset
Classification
High-Risk Germline Expansion Route
5. MATERNAL EXPANSION PATHWAY
Characteristics
- Greater repeat stability
- Smaller repeat changes
- Lower expansion frequency
Outcome
Parent
45 CAG
↓
Child
46–48 CAG
Classification
Moderate-Stability Transmission Route
6. ANTICIPATION ATLAS
Definition
Progressive earlier disease onset across generations.
Mechanism
Inherited Expansion
↓
Larger CAG Length
↓
Earlier Neurotoxicity
↓
Earlier Symptom Onset
Primary Driver
Paternal Expansion
Atlas Output
Family Expansion Trees
Generation-by-Generation:
- CAG length
- Age of onset
- Disease severity
7. GERMLINE EXPANSION CLASSIFICATION
Class | Description |
G-I | Stable transmission |
G-II | Minor expansion |
G-III | Moderate expansion |
G-IV | Major expansion |
G-V | Juvenile-risk expansion |
8. SOMATIC EXPANSION ATLAS
Definition
Progressive increase in CAG repeat length after birth within tissues.
Importance
Now recognized as a major disease progression mechanism.
Core Concept
A patient inherits one repeat length but develops many tissue-specific repeat lengths over time.
Example:
Inherited:
45 CAG
↓
Striatum:
80–120+ CAG
↓
Neuronal Toxicity
9. SOMATIC EXPANSION BIOLOGY
Stage 1
Inherited Repeat
↓
Stage 2
DNA Damage
↓
Stage 3
Repair Attempt
↓
Stage 4
Repair Error
↓
Stage 5
Repeat Expansion
↓
Stage 6
Progressive Accumulation
10. DNA REPAIR DRIVERS OF SOMATIC EXPANSION
Expansion Accelerators
MSH3
Role:
Mismatch Repair
Classification:
Major Expansion Driver
MSH2
Classification:
Expansion Driver
MLH1
Classification:
Expansion Driver
PMS1
Classification:
Expansion Driver
PMS2
Classification:
Expansion Driver
11. SOMATIC EXPANSION SUPPRESSORS
FAN1
Function:
Fork protection
Effect:
Reduced expansion
Additional Candidate Modifiers
- BRCA1
- BRCA2
- ATM
- ATR
12. TISSUE-SPECIFIC EXPANSION ATLAS
Very High Expansion
Caudate Nucleus
Vulnerability:
Extreme
Putamen
Vulnerability:
Extreme
Medium Spiny Neurons
Vulnerability:
Extreme
13. HIGH EXPANSION TISSUES
Frontal Cortex
Motor Cortex
Hippocampus
14. MODERATE EXPANSION TISSUES
Cerebellum
Blood Cells
Peripheral Tissues
15. LOW EXPANSION TISSUES
Skeletal Muscle
Fibroblasts
16. CELL-TYPE VULNERABILITY ATLAS
Cell Type | Expansion Burden |
Medium Spiny Neurons | Very High |
Cortical Projection Neurons | High |
Astrocytes | Moderate |
Microglia | Moderate |
Peripheral Lymphocytes | Low |
17. SOMATIC EXPANSION CLASSIFICATION
Class | Description |
S-I | Minimal expansion |
S-II | Mild expansion |
S-III | Moderate expansion |
S-IV | Severe expansion |
S-V | Hyper-expansion state |
18. RNA CONSEQUENCES OF SOMATIC EXPANSION
Expanded HTT Transcript
Effects:
- RNA instability
- Splicing abnormalities
- RNA toxicity
19. PROTEIN CONSEQUENCES OF SOMATIC EXPANSION
Expanded PolyQ Domain
Effects:
- Misfolding
- Aggregate formation
- Proteostasis failure
20. NEUROIMMUNE CONSEQUENCES
Somatic Expansion
↓
Protein Toxicity
↓
Microglial Activation
↓
Inflammation
↓
Further Injury
21. STRANDSHIFT EXPANSION HIERARCHY
Tier I
Germline Expansion
Origin Layer
Tier II
Inherited HTT Genotype
Genetic Layer
Tier III
Somatic Expansion
Amplification Layer
Tier IV
RNA Toxicity
Molecular Injury Layer
Tier V
Protein Misfolding
Proteotoxic Layer
Tier VI
Neuroimmune Activation
Inflammatory Layer
Tier VII
Neurodegeneration
Clinical Disease Layer
22. COMPOSITE EXPANSION INDICES
Germline Expansion Index (GEI)
Measures:
- Parent-child expansion
- Anticipation burden
- Transmission instability
Somatic Expansion Index (SEI)
Measures:
- Tissue-specific expansion
- Age-adjusted expansion
- Cellular heterogeneity
Expansion Toxicity Index (ETI)
Measures:
- Expansion burden
- Aggregate burden
- Cellular dysfunction
STRANDSHIFT Expansion Burden Score (SEBS)
Integrated score combining:
- Germline burden
- Somatic burden
- Tissue vulnerability
- Modifier-gene profile
23. PRIMARY DELIVERABLES
- Germline Expansion Atlas
- Somatic Expansion Atlas
- Anticipation Mapping Database
- Tissue Vulnerability Atlas
- Cell-Type Vulnerability Atlas
- Modifier-Gene Network Atlas
- Germline Expansion Index
- Somatic Expansion Index
- Expansion Toxicity Index
- STRANDSHIFT Expansion Burden Score
24. KEY CONCLUSIONS
Germline Expansion
Determines inherited disease risk and anticipation.
Somatic Expansion
Determines tissue-specific toxicity and disease progression.
Central STRANDSHIFT Model
Huntington disease severity is governed by the interaction between:
Inherited CAG Length
×
Somatic Expansion Dynamics
×
DNA Repair Modifier Activity
=
Clinical Disease Expression
MASTER REGISTRY INDEX
SCF-AMC-STRANDSHIFT-GSEA-0001 — Germline vs Somatic Expansion Atlas
SCF-AMC-STRANDSHIFT-GEA-0001 — Germline Expansion Atlas
SCF-AMC-STRANDSHIFT-SEA-0001 — Somatic Expansion Atlas
SCF-AMC-STRANDSHIFT-AMD-0001 — Anticipation Mapping Database
SCF-AMC-STRANDSHIFT-TVA-0001 — Tissue Vulnerability Atlas
SCF-AMC-STRANDSHIFT-CVA-0001 — Cell-Type Vulnerability Atlas
SCF-AMC-STRANDSHIFT-MGN-0001 — Modifier-Gene Network Atlas
SCF-AMC-STRANDSHIFT-GEI-0001 — Germline Expansion Index
SCF-AMC-STRANDSHIFT-SEI-0001 — Somatic Expansion Index
SCF-AMC-STRANDSHIFT-SEBS-0001 — STRANDSHIFT Expansion Burden Score
SCF-AMC-STRANDSHIFT-HMOA-0001 — HTT Mutation Origin Analysis
SCF-AMC-STRANDSHIFT-EPC-0001 — Etiopathogenic Core Report
SCF-AMC-STRANDSHIFT-0001 — PROJECT STRANDSHIFT
SCF-DMRD-MASTER-0001 — SCF Advanced Disease Modeling & Discovery