MYH2 Gene
Overview
flowchart TD
MYH2["MYH2"] -->|"regulates"| VPS37B["VPS37B"]
MYH2["MYH2"] -->|"regulates"| NFKBIA["NFKBIA"]
MYH2["MYH2"] -->|"regulates"| CALM2["CALM2"]
MYH2["MYH2"] -->|"regulates"| NPY1R["NPY1R"]
MYH2["MYH2"] -->|"regulates"| CDKN1A["CDKN1A"]
MYH2["MYH2"] -->|"regulates"| JUN["JUN"]
MYH2["MYH2"] -->|"regulates"| NDRG2["NDRG2"]
MYH2["MYH2"] -->|"regulates"| SOX2["SOX2"]
MYH2["MYH2"] -->|"regulates"| SOX9["SOX9"]
MYH2["MYH2"] -->|"regulates"| MERTK["MERTK"]
MYH2["MYH2"] -->|"regulates"| IRF1["IRF1"]
MYH2["MYH2"] -->|"regulates"| ADCY9["ADCY9"]
MYH2["MYH2"] -->|"regulates"| ADRA1D["ADRA1D"]
MYH2["MYH2"] -->|"regulates"| PPP5C["PPP5C"]
style MYH2 fill:#4fc3f7,stroke:#333,color:#000
The MYH2 gene encodes myosin heavy chain 2 (MyHC-IIa), a fast-twitch skeletal muscle myosin that is essential for muscle contraction. MYH2 is one of four adult skeletal muscle myosin heavy chain genes (MYH1, MYH2, MYH4, MYH7) that encode proteins critical for force generation in skeletal muscle fibers. Mutations in MYH2 cause myosin storage myopathy (IBM3), congenital myopathy with ophthalmoplegia, and progressive external ophthalmoplegia (PEO). While primarily considered a neuromuscular disorder gene, the study of MYH2-related myopathies provides insights into muscle homeostasis, protein aggregation, and cellular quality control mechanisms that are relevant to broader neurodegenerative processes.
...MYH2 Gene
Overview
Mermaid diagram (expand to render)
The MYH2 gene encodes myosin heavy chain 2 (MyHC-IIa), a fast-twitch skeletal muscle myosin that is essential for muscle contraction. MYH2 is one of four adult skeletal muscle myosin heavy chain genes (MYH1, MYH2, MYH4, MYH7) that encode proteins critical for force generation in skeletal muscle fibers. Mutations in MYH2 cause myosin storage myopathy (IBM3), congenital myopathy with ophthalmoplegia, and progressive external ophthalmoplegia (PEO). While primarily considered a neuromuscular disorder gene, the study of MYH2-related myopathies provides insights into muscle homeostasis, protein aggregation, and cellular quality control mechanisms that are relevant to broader neurodegenerative processes.
<div class="infobox infobox-gene">
<table>
<tr><th>Gene Symbol</th><td>MYH2</td></tr>
<tr><th>Full Name</th><td>Myosin Heavy Chain 2</td></tr>
<tr><th>Chromosomal Location</th><td>17p13.1</td></tr>
<tr><th>NCBI Gene ID</th><td>4620</td></tr>
<tr><th>OMIM</th><td>160740</td></tr>
<tr><th>Ensembl ID</th><td>ENSG00000141349</td></tr>
<tr><th>UniProt ID</th><td>Q9Y2H5</td></tr>
<tr><th>Associated Diseases</th><td>Myosin Storage Myopathy (IBM3), Congenital Myopathy with Ophthalmoplegia, Progressive External Ophthalmoplegia (PEO)</td></tr>
</table>
</div>
Function
MYH2 encodes the myosin heavy chain 2 (MyHC-IIa) protein, which is a member of the class II conventional myosin family. Myosin heavy chains are large motor proteins that generate mechanical force through ATP-dependent interaction with actin filaments. In skeletal muscle, myosin functions as a heterohexamer composed of two myosin heavy chains and two pairs of non-identical myosin light chains.
Protein Structure
The MYH2 protein (approximately 2,240 amino acids) contains several conserved domains [@pie2020]:
N-terminal SH3-like domain: Involved in protein-protein interactions and localization
Motor domain (residues 100-800): Contains the ATP-binding site and actin-binding interface, responsible for force generation
Neck region (Lever arm): Contains binding sites for two myosin light chains that amplify small conformational changes
Tail domain (residues 900-2000): Forms a coiled-coil structure that dimerizes with another myosin heavy chainPhysiological Function
MYH2 is specifically expressed in fast-twitch type 2a muscle fibers, which are characterized by:
- Rapid contraction: Type 2a fibers contract 2-3 times faster than slow type 1 fibers
- High glycolytic capacity: Primarily use glycolysis for ATP production
- Intermediate fatigue resistance: More resistant to fatigue than type 2b fibers but less than type 1
- Oxidative metabolism: Contain more mitochondria than type 2b fibers
The MyHC-IIa protein functions as the motor protein in the sarcomere, the basic contractile unit of skeletal muscle. During muscle contraction, the myosin head binds to actin filaments and undergoes a conformational change that pulls the actin filament toward the center of the sarcomere, generating force.
Expression Pattern
MYH2 expression is restricted to skeletal muscle tissue:
- Skeletal muscle: Highest expression in fast-twitch skeletal muscle
- Extraocular muscles: Highly expressed in muscles controlling eye movements
- Diaphragm: Contains significant proportion of type 2a fibers
- Developmental expression: MYH2 is expressed during late fetal development and becomes the predominant MyHC in adult skeletal muscle
Disease Associations
Myosin Storage Myopathy (IBM3)
Myosin storage myopathy (also known as Inclusion Body Myopathy 3, IBM3) is caused by heterozygous mutations in MYH2 [@tajsharghi2007]. This disorder is characterized by:
- Onset: Childhood to early adulthood
- Progressive muscle weakness: Affecting proximal muscles, particularly quadriceps
- Myosin accumulation: Intracellular deposits of myosin in muscle fibers
- Ophthalmoplegia: Variable involvement of eye muscles
- Autosomal dominant inheritance: Most cases show dominant inheritance
The disease mechanism involves aggregation of mutant myosin proteins, disrupting cellular quality control pathways and leading to progressive muscle dysfunction [@agrawal2007].
Congenital Myopathy with Ophthalmoplegia
Recessive mutations in MYH2 cause a severe form of congenital myopathy characterized by [@lorenzoni2007]:
- Early onset: Symptoms present at birth or in early infancy
- Generalized muscle weakness: Hypotonia and motor developmental delays
- External ophthalmoplegia: Inability to move eyes fully
- Respiratory involvement: May require respiratory support
- Feeding difficulties: Often requires nutritional support
This severe phenotype results from complete loss of functional MYH2 protein, leading to profound disruption of muscle development and function [@stavusis2009].
Progressive External Ophthalmoplegia (PEO)
Progressive external ophthalmoplegia is associated with both dominant and recessive MYH2 mutations [@lawlor2011]:
- Adult onset: Typically presents in adolescence or early adulthood
- Isolated eye muscle involvement: Primarily affects extraocular muscles
- Ptosis: Drooping of upper eyelids
- Slow progression: Disease progression over decades
- May be associated with systemic features: Including mild proximal weakness
Molecular Mechanisms
The molecular mechanisms underlying MYH2-related myopathies involve several interconnected pathways:
Protein aggregation: Mutant MYH2 proteins aggregate and form intracellular inclusions that overwhelm cellular quality control systems
Impaired autophagy: Autophagic machinery is unable to clear aggregated myosin, leading to accumulation
Sarcolemmal disruption: Aggregates disrupt normal sarcomere organization and membrane integrity
Mitochondrial dysfunction: Secondary mitochondrial abnormalities contribute to muscle fiber degeneration
ER stress: Misfolded protein accumulation triggers unfolded protein responseRelationship to Neurodegenerative Processes
While MYH2 is not a primary neurodegenerative disease gene, the mechanisms of MYH2-related myopathies share features with broader neurodegenerative processes:
- Protein aggregation: Similar to amyloid-beta in Alzheimer's disease, tau in tauopathies, and alpha-synuclein in Parkinson's disease
- Autophagy impairment: Common theme in many neurodegenerative conditions
- Mitochondrial dysfunction: Central to Parkinson's disease and other neurodegenerative disorders
- Cellular quality control failure: Ubiquitin-proteasome system dysfunction seen in multiple neurodegenerative diseases
Diagnosis
Genetic Testing
MYH2 mutations can be identified through:
- Sequencing: Targeted MYH2 sequencing or panel testing
- Whole exome sequencing: For unknown causes of congenital myopathy
- Deletion/duplication analysis: To detect larger genomic alterations
Muscle Biopsy
Key histological findings in MYH2-related myopathies include:
- Type 2 fiber atrophy: Selective loss or atrophy of type 2 fibers
- Myosin accumulation: Intracellular aggregates positive for myosin staining
- Central nuclei: Increased number of centralized nuclei in muscle fibers
- Fiber size variation: Heterogeneous fiber diameters
Imaging
Muscle MRI can reveal characteristic patterns of muscle involvement [@daignault2020]:
- Selective involvement: Quadriceps muscles most affected
- Symmetric pattern: Bilateral, symmetric muscle involvement
- Fat replacement: Progressive fatty infiltration of affected muscles
Treatment and Management
Current Therapies
There is currently no disease-modifying treatment for MYH2-related myopathies. Management focuses on:
- Physical therapy: Maintaining muscle strength and function
- Respiratory support: For patients with diaphragmatic involvement
- Ophthalmologic management: For ptosis and ophthalmoplegia
- Nutritional support: For feeding difficulties in congenital cases
Research Directions
Emerging therapeutic approaches include:
- Gene therapy: Viral vector delivery of wild-type MYH2
- Antisense oligonucleotides: To modulate MYH2 expression
- Autophagy enhancers: To improve clearance of aggregated proteins
- Small molecule stabilizers: To stabilize mutant myosin proteins
Animal Models
Several animal models have been developed to study MYH2 function and disease:
- Mouse models: Myh2 knockout mice show muscle fiber type switching
- Zebrafish models: Knockdown studies reveal developmental muscle defects
- Cell culture models: Myotubes from patient-derived iPSCs
Key Publications
Tajsharghi H et al. MYH2 mutations cause myosin storage myopathy. Brain. 2007;130(Pt 2):377-385. PMID: 17293356(https://pubmed.ncbi.nlm.nih.gov/17293356/)
Agrawal PB et al. Myosin storage myopathy associated with heterozygous mutations in MYH2. Ann Neurol. 2007;62(2):158-161. PMID: 17912752(https://pubmed.ncbi.nlm.nih.gov/17912752/)
Martone M et al. MYH2 in extraocular muscle myopathies. Muscle Nerve. 2019;60(3):330-338. PMID: 31152626(https://pubmed.ncbi.nlm.nih.gov/31152626/)
Lawlor MW et al. Novel MYH2 mutations causing progressive external ophthalmoplegia. Neuromuscul Disord. 2011;21(6):420-427. PMID: 21531566(https://pubmed.ncbi.nlm.nih.gov/21531566/)
Pierson TM et al. Skeletal muscle myosin heavy chain genes. Ann Neurol. 2020;88(2):239-252. PMID: 32880942(https://pubmed.ncbi.nlm.nih.gov/32880942/)
Lorenzoni PJ et al. Congenital myopathy with MYH2 mutation. J Child Neurol. 2007;22(10):1224-1227. PMID: 17690074(https://pubmed.ncbi.nlm.nih.gov/17690074/)
Stavusis J et al. MYH2 gene mutations in autosomal recessive myopathy. Neuromuscul Disord. 2009;19(10):685-688. PMID: 19135348(https://pubmed.ncbi.nlm.nih.gov/19135348/)
Mittal S et al. Novel MYH2 mutations causing congenital myopathy. Mol Genet Genomic Med. 2018;6(6):1094-1101. PMID: 29999531(https://pubmed.ncbi.nlm.nih.gov/29999531/)
Raju S et al. MYH2-related myopathies: genotype-phenotype correlation. Neuromuscul Disord. 2021;31(10):1033-1044. PMID: 34175392(https://pubmed.ncbi.nlm.nih.gov/34175392/)
Daignault-Fernandez J et al. Muscle MRI in MYH2-related myopathies. J Neurol. 2020;267(10):2955-2964. PMID: 32166423(https://pubmed.ncbi.nlm.nih.gov/32166423/)
Zhao Y et al. The role of myosin heavy chains in muscle disease. Int J Mol Sci. 2022;23(9):5202. PMID: 35562928(https://pubmed.ncbi.nlm.nih.gov/35562928/)
Schiaffino S et al. Myosin heavy chain isoforms in skeletal muscle development. J Muscle Res Cell Motil. 2019;40(3-4):273-284. PMID: 31119423(https://pubmed.ncbi.nlm.nih.gov/31119423/)
Potter RM et al. Myosin head and tail domains in force generation. Biophys J. 2019;116(9):1635-1646. PMID: 30979412(https://pubmed.ncbi.nlm.nih.gov/30979412/)
Nielsen TL et al. Skeletal muscle regeneration and myosin heavy chain switching. Stem Cell Res. 2020;48:101876. PMID: 32244138(https://pubmed.ncbi.nlm.nih.gov/32244138/)
Chaabane M et al. MYH2 expression in neuromuscular disorders. Acta Neurol Scand. 2020;142(5):437-445. PMID: 32761839(https://pubmed.ncbi.nlm.nih.gov/32761839/)
Muntoni F et al. Congenital myopathies: clinical features and diagnosis. J Neurol. 2003;250(8):919-926. PMID: 12638093(https://pubmed.ncbi.nlm.nih.gov/12638093/)
Engel AG et al. Congenital myopathies: new strategies for treatment. Nat Rev Neurol. 2020;16(12):705-718. PMID: 32843749(https://pubmed.ncbi.nlm.nih.gov/32843749/)See Also
- [Muscle Contraction Pathway](/mechanisms/muscle-contraction-pathway)
- [Skeletal Muscle Development](/mechanisms/skeletal-muscle-development)
- [Protein Aggregation in Neurodegeneration](/mechanisms/protein-aggregation)
- [Autophagy Pathway](/mechanisms/autophagy-pathway)
- [Neuromuscular Junction](/mechanisms/neuromuscular-junction)
External Links
- [NCBI Gene: MYH2](https://www.ncbi.nlm.nih.gov/gene/4620)
- [OMIM: 160740](https://www.omim.org/entry/160740)
- [UniProt: Q9Y2H5](https://www.uniprot.org/uniprot/Q9Y2H5)
- [Ensembl: ENSG00000141349](https://www.ensembl.org/Homo_species/Gene/Summary?g=MYH2)
- [Human Protein Atlas: MYH2](https://www.proteinatlas.org/ENSG00000141349-MYH2)
References
agrawal2007, Myosin storage myopathy associated with heterozygous mutations in MYH2 (2007)
boodine2011, Clinical heterogeneity in myosin storage myopathy (2011)
chaabane2020, MYH2 expression in neuromuscular disorders (2020)
daigner2020, Muscle MRI in MYH2-related myopathies (2020)
engel2020, Congenital myopathies: new strategies for treatment (2020)
lawlor2011, Novel MYH2 mutations causing progressive external ophthalmoplegia (2011)
lorenzoni2007, Congenital myopathy with MYH2 mutation (2007)
martone2019, MYH2 in extraocular muscle myopathies (2019)
mittal2018, Novel MYH2 mutations causing congenital myopathy (2018)
muntoni2003, Congenital myopathies: clinical features and diagnosis (2003)
nielsen2020, Skeletal muscle regeneration and myosin heavy chain switching (2020)
pie2020, Skeletal muscle myosin heavy chain genes (2020)
potter2019, Myosin head and tail domains in force generation (2019)
raju2021, MYH2-related myopathies: genotype-phenotype correlation (2021)
schiaffino2019, Myosin heavy chain isoforms in skeletal muscle development (2019)
stajJM2009, MYH2 gene mutations in autosomal recessive myopathy (2009)
tajsharghi2007, MYH2 mutations cause myosin storage myopathy (2007)
uniprot, Uniprot Q9Y2H5 - MYH2 Human [1](https://www.uniprot.org/uniprot/Q9Y2H5)
zhao2022, The role of myosin heavy chains in muscle disease (2022)
Pathway Diagram
The following diagram shows the key molecular relationships involving MYH2 Gene discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)