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MYO3A
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MYO3A

MYO3A encodes myosin IIIA, a specialized motor protein with both actin-based movement and kinase activity, essential for maintaining the structure and function of inner ear hair cell stereocilia. 

Mutations in MYO3A are linked to progressive, nonsyndromic sensorineural hearing loss and are under investigation for potential roles in vision and cancer biology.

What is MYO3A (Myosin IIIA)?

The MYO3A gene, located on chromosome 10p12.1, encodes myosin IIIA, a non-muscle motor protein with a unique combination of actin-based motor activity and serine/threonine kinase activity. 

Unlike conventional myosins involved in muscle contraction, MYO3A plays a specialized role in sensory cells. It is primarily expressed in inner ear hair cells, where it is essential for hearing, and in retinal photoreceptors, where it may contribute to visual function. 

MYO3A is also expressed in the testis and has been detected in some cancer cells.

MYO3A: A Non-Muscle Myosin with Diverse Functions

MYO3A is vital for maintaining the architecture and function of stereocilia, the actin-rich projections of sensory hair cells in the inner ear that detect sound. It helps regulate the size and number of stereocilia and contributes to the staircase structure crucial for mechanotransduction. 

MYO3A also acts as a transporter, delivering actin-binding proteins like espin-1 to the tips of stereocilia. Its localization to stereocilia depends on interactions with MORN4 and PCDH15, a key component of the mechanotransduction complex. 

These functions support both the development and maintenance of auditory hair cells and, potentially, similar structures in the retina.

When is MYO3A Testing or Research Relevant?

MYO3A genetic testing may be considered in the following scenarios:

Genetic Hearing Loss

MYO3A mutations are a well-established cause of nonsyndromic sensorineural hearing loss (SNHL), and genetic testing can be clinically useful in select cases:

  • Autosomal Recessive DFNB30: Caused by biallelic loss-of-function variants, leading to progressive, bilateral hearing loss typically beginning in childhood or adolescence.
  • Autosomal Dominant DFNA90: Caused by dominant-negative missense variants. Onset and severity may vary, with some individuals developing hearing loss later in life.

Genetic testing for MYO3A mutations should be considered in individuals with:

Emerging Areas of Research

While hearing loss remains the primary clinical concern, MYO3A is also being studied in other contexts:

Cancer

Altered MYO3A expression may influence tumor cell migration and invasion, though this remains under investigation.

Vision

Given its retinal expression, MYO3A may contribute to visual processes. Possible roles are still being explored.

MYO3A Genetic Testing: Test Procedure and Interpretation

Testing for MYO3A is performed as a genetic test to look for mutations in the gene that would alter functional protein availability. The following section outlines the testing procedures and interpretation.

Testing Procedure and Preparation

Genetic testing involves blood, saliva, or cheek swab samples, although specialized laboratories may recommend different sample types. 

A cheek swab or saliva sample is easily obtained from the comfort of home, while blood samples typically require a blood draw.

Normal Reference Ranges

Normal reference ranges for MYO3A genetic testing are considered to be without mutations that can alter the activity of the MYO3A proteins.

What Do Mutations in MYO3A Mean?

MYO3A mutations may have the following clinical significance:

Hearing Loss

Mutations in MYO3A are a rare cause of hearing loss. These mutations interfere with stereocilia structure, actin transport, and protein localization, resulting in disrupted sound transduction and progressive hearing loss. The effects differ by mutation:

  • Recessive variants (e.g., p.Tyr1043Ter): Cause complete or partial loss of function and require mutations in both gene copies to cause disease.
  • Dominant variants (e.g., p.Leu697Trp, p.Gly488Glu, p.Leu239Pro): Exert a dominant-negative effect by interfering with the function of the normal protein. These mutations may reduce ATPase activity, increase actin affinity, and impair the localization or motility of MYO3A.

Cancer

Some studies suggest MYO3A might influence cancer progression by affecting cell shape, motility, or adhesion. However, its precise role in cancer biology remains unclear and is not yet clinically actionable.

What Does the Absence of MYO3A Variants Mean?

A negative MYO3A test result—meaning no known pathogenic variants were identified—does not exclude a genetic contribution to hearing loss or other MYO3A-related conditions. 

Many cases of progressive SNHL are multifactorial and may involve other genes or non-coding variants not assessed by routine tests. Therefore, MYO3A results must be interpreted in the broader context of clinical presentation, family history, and other diagnostic findings.

Clinical Takeaways

MYO3A encodes an unconventional myosin motor protein critical for maintaining inner ear stereocilia. Its dysfunction can lead to progressive sensorineural hearing loss through inherited recessive or dominant mutations. 

Clinicians should consider MYO3A testing when evaluating patients with:

  • Progressive, bilateral, nonsyndromic hearing loss
  • A family history of autosomal recessive or dominant inheritance patterns
  • Late-childhood or adult-onset hearing loss, especially if audiograms show high-frequency loss

Additional clinical considerations include:

  • Recessive MYO3A-related hearing loss often begins in the second or third decade of life and progresses to severe or profound levels.
  • Dominant MYO3A variants may have later onset with variable severity and incomplete penetrance.
  • Audiologic monitoring and early intervention with hearing aids or cochlear implants can improve outcomes.
  • Genetic counseling is strongly recommended for families affected by MYO3A-related hearing loss, particularly in consanguineous populations or those with multiple affected members.

In research contexts, MYO3A remains a key target in sensory biology. Future therapies may explore restoring stereocilia structure or compensating for MYO3A dysfunction through actin-regulatory proteins or gene-specific strategies.

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See References

606808 MYOSIN IIIA; MYO3A [Review of * 606808 MYOSIN IIIA; MYO3A]. OMIM; OMIM. https://omim.org/entry/606808

Baghel KS, Tewari BN, Shrivastava R, Malik SA, Lone MU, Jain NK, Tripathi C, Kanchan RK, Dixit S, Singh K, Mitra K, Negi MP, Srivastava M, Misra S, Bhatt ML, Bhadauria S. Macrophages promote matrix protrusive and invasive function of breast cancer cells via MIP-1β dependent upregulation of MYO3A gene in breast cancer cells. Oncoimmunology. 2016 Jul 15;5(7):e1196299. doi: 10.1080/2162402X.2016.1196299. PMID: 27622050; PMCID: PMC5006911.

Dantas, V.G.L., Raval, M.H., Ballesteros, A. et al. Characterization of a novel MYO3A missense mutation associated with a dominant form of late onset hearing loss. Sci Rep 8, 8706 (2018). https://doi.org/10.1038/s41598-018-26818-2

Doll, J., Michaela, Bahena, P., Heihoff, A., Segebarth, D., Müller, T., Dittrich, M., Haaf, T., & Vona, B. (2020). A novel missense variant in MYO3A is associated with autosomal dominant high‐frequency hearing loss in a German family. Molecular Genetics & Genomic Medicine, 8(8). https://doi.org/10.1002/mgg3.1343

Grati M, Yan D, Raval MH, Walsh T, Ma Q, Chakchouk I, Kannan-Sundhari A, Mittal R, Masmoudi S, Blanton SH, Tekin M, King MC, Yengo CM, Liu XZ. MYO3A Causes Human Dominant Deafness and Interacts with Protocadherin 15-CD2 Isoform. Hum Mutat. 2016 May;37(5):481-7. doi: 10.1002/humu.22961. Epub 2016 Feb 16. PMID: 26841241; PMCID: PMC4833613.

Maekawa, K., Nishio, S., Miyazaki, H., Ohta, Y., Oishi, N., Kasai, M., Yamamoto, A., Mayuri Okami, Koichiro Wasano, Sakai, A., & Shin-ichi Usami. (2025). The Prevalence and Clinical Characteristics of MYO3A-Associated Hearing Loss in 15,684 Hearing Loss Patients. Genes, 16(1), 92–92. https://doi.org/10.3390/genes16010092

MYO3A myosin IIIA [ Homo sapiens (human) ] Gene ID: 53904 [Review of MYO3A myosin IIIA [ Homo sapiens (human) ] Gene ID: 53904]. National Library of Medicine: National Center for Biotechnology Information. https://www.ncbi.nlm.nih.gov/gene/53904

MYO3A Gene - GeneCards | MYO3A Protein | MYO3A Antibody. (n.d.). Www.genecards.org. https://www.genecards.org/cgi-bin/carddisp.pl?gene=MYO3A

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