MSH3 (MutS Homolog 3) encodes a key DNA mismatch repair (MMR) protein that forms the MutSβ heterodimer with MSH2. This complex recognizes and repairs small insertion/deletion loops (IDLs) that arise during DNA replication, maintaining genomic stability.
MSH3 (MutS Homolog 3) encodes a key DNA mismatch repair (MMR) protein that forms the MutSβ heterodimer with MSH2. This complex recognizes and repairs small insertion/deletion loops (IDLs) that arise during DNA replication, maintaining genomic stability.
Role in Mismatch Repair
MSH3 participates in DNA mismatch repair by:
Forming MSH2-MSH3 (MutSβ) heterodimer
Recognizing base-base mismatches and small insertion/deletion loops
Initiating the MMR repair cascade
Mediating DNA damage response signaling
MSH3 in Repeat Expansion
Beyond canonical MMR, MSH3 plays a critical role in protecting against CAG/CTG repeat expansions[1]. MSH3 deficiency leads to dramatically increased somatic repeat expansion in [neurons](/entities/neurons), contributing to neurodegenerative diseases.
Disease Associations
Amyotrophic Lateral Sclerosis (ALS)
MSH3 is a major genetic risk factor for ALS. GWAS studies have identified MSH3 variants associated with increased ALS risk[2]. MSH3 deficiency leads to:
Increased DNA damage accumulation in motor neurons
Enhanced CAG repeat expansion in the ATXN2 gene
Accelerated disease progression in animal models
Huntington's Disease
MSH3 modulates HD pathogenesis through its role in somatic CAG repeat expansion[3]. MSH3 knockout mice show dramatically accelerated polyglutamine expansion in striatal neurons.
Colorectal Cancer
As a MMR gene, MSH3 loss contributes to microsatellite instability (MSI) and colorectal carcinogenesis. MSH3-deficient tumors show high mutation burden.
Expression Patterns
| Brain Region | Expression Level | |--------------|-----------------| | Motor [Cortex](/brain-regions/cortex) | High | | Spinal Cord | High (motor neurons) | | Striatum | High | | Cerebellum | Moderate | | [Hippocampus](/brain-regions/hippocampus) | Moderate |
Common Variants
| Variant | Type | Function | Associated Phenotype | |---------|------|----------|---------------------| | p.R497H | Missense | Partial loss | ALS risk modifier | | p.T707A | Missense | Neutral | Common polymorphism | | c.2146-1G>A | Splicing | Loss | Colorectal cancer |
Therapeutic Implications
MSH3 as Therapeutic Target
MSH3 inhibitors: Under investigation for cancer combination therapy
Gene therapy: AAV-delivered MSH3 for neuroprotection
DNA Damage Response Modulation
PARP inhibitors may be synthetically lethal with MSH3 deficiency
ATM/ATR inhibitors to enhance DNA damage sensitivity in MSH3-deficient cells
See Also
[DNA Damage and Repair](/mechanisms/dna-damage-repair)