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OTOF
otoferlin
OTOF is located on the short (p) arm of chromosome 2, at band 2p23.3. Arm ratio per GRCh38 - banding schematic.
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Overview
The OTOF gene encodes otoferlin, a large membrane-associated protein that plays an indispensable role in hearing. Located on chromosome 2, this gene is expressed predominantly in the inner hair cells of the cochlea, where otoferlin coordinates the release of chemical neurotransmitters in response to sound stimulation. Without functional otoferlin, the conversion of mechanical sound waves into neural signals becomes profoundly impaired. Pathogenic changes in OTOF represent one of the most common genetic causes of non-syndromic auditory neuropathy, a condition characterised by preserved cochlear function but disrupted auditory nerve signalling. Understanding OTOF is particularly relevant for genetic carrier screening and early diagnostic testing in individuals with unexplained hearing loss.
What the gene does
Otoferlin functions as a calcium sensor that orchestrates synaptic vesicle fusion at the specialised ribbon synapses of cochlear inner hair cells. When sound vibrations reach the inner ear, they cause hair cell depolarisation and calcium influx. Otoferlin detects these calcium changes and triggers the rapid, sustained release of glutamate neurotransmitter onto auditory nerve fibres. This process must occur with extraordinary speed and precision to faithfully encode the temporal features of sound, including pitch and rhythm. The protein contains multiple calcium-binding C2 domains that enable it to respond to varying calcium concentrations, allowing hair cells to sustain neurotransmitter release over prolonged periods of stimulation. Otoferlin also participates in the subsequent retrieval and recycling of synaptic vesicles, ensuring that hair cells maintain a ready pool of vesicles for continuous sound encoding. Research suggests that otoferlin may additionally stabilise the structural organisation of ribbon synapses, contributing to the maintenance of synaptic integrity throughout life.
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Chromosome location
OTOF is located on the short arm of chromosome 2 at position 2p23.3. The gene spans a substantial genomic region and comprises 48 exons, reflecting the complexity of the large otoferlin protein it encodes. This chromosomal location is distant from other major hearing-loss genes, and the gene's size makes it susceptible to a diverse array of pathogenic variants across its coding sequence.
Protein structure
Otoferlin is a large protein of 1,997 amino acids with a modular architecture dominated by seven C2 domains. The protein begins with C2 1 at amino acids 1-98, followed by C2 2 spanning amino acids 236-357, C2 3 from amino acids 400-531, C2 4 covering amino acids 944-1,069, C2 5 extending from amino acids 1,115-1,242, C2 6 located at amino acids 1,464-1,593, and C2 7 occupying amino acids 1,714-1,865. These C2 domains are interspersed with disordered regions at amino acids 128-171, 642-694, 1,299-1,324, and 1,343-1,405, which likely provide flexibility for protein interactions and conformational changes. A coiled coil region at amino acids 792-821 may facilitate protein oligomerisation or interaction with synaptic machinery. The multiple C2 domains allow otoferlin to bind calcium ions with varying affinities, enabling the protein to decode different calcium signals during synaptic transmission and vesicle trafficking.
Key variants
Pathogenic variants in OTOF are distributed across the entire coding sequence, with loss-of-function variants-including nonsense, frameshift, and splice-site changes-commonly identified. Missense variants affecting the C2 domains can disrupt calcium binding or impair the protein's ability to trigger vesicle fusion. The inheritance pattern for OTOF-related hearing loss is typically autosomal recessive, meaning that individuals require pathogenic variants in both gene copies to manifest auditory neuropathy. Certain populations exhibit founder mutations, where specific variants occur at higher frequencies due to shared ancestry.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.1366_1367insC | p.Val456fs | Pathogenic/Likely pathogenic | ★★☆☆ | OTOF-related disorder |
c.1498C>T | p.Arg500Ter | Pathogenic | ★★☆☆ | Nonsyndromic genetic hearing loss |
c.3289-1G>C | - | Pathogenic/Likely pathogenic | ★★☆☆ | Autosomal recessive nonsyndromic hearing loss 9 |
c.1310dup | p.Met437fs | Pathogenic | ★☆☆☆ | not provided |
c.1469dup | p.Leu491fs | Pathogenic | ★☆☆☆ | not provided |
c.3166del | p.Leu1056fs | Pathogenic | ★☆☆☆ | not provided |
c.3864+2T>A | - | Pathogenic | ★☆☆☆ | not provided |
c.409G>T | p.Glu137Ter | Pathogenic | ★☆☆☆ | not provided |
c.4158_4159del | p.Gln1387fs | Pathogenic | ★☆☆☆ | Autosomal recessive nonsyndromic hearing loss 9 |
c.4809C>G | p.Tyr1603Ter | Pathogenic | ★☆☆☆ | OTOF-related disorder |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Pathogenic variants in OTOF cause auditory neuropathy (OTOF), a form of non-syndromic hearing loss characterised by impaired sound signal transmission from the cochlea to the brain. Affected individuals often show preserved outer hair cell function on audiological testing but demonstrate absent or severely abnormal auditory brainstem responses, reflecting disrupted neural signalling. The severity of hearing loss can range from moderate to profound, and some individuals may experience fluctuating hearing ability. Auditory neuropathy due to OTOF typically presents in infancy or early childhood, though the precise age of onset and progression can vary. Importantly, this condition affects hearing selectively, without involvement of other organ systems.
UK clinical status
OTOF is included on multiple NHS Genomic Medicine Service gene panels for hereditary hearing disorders. The gene holds green classification status on the Auditory Neuropathy Spectrum Disorder panel and the Monogenic Hearing Loss panel (version R67), indicating strong evidence for its role in these conditions. This classification supports the use of OTOF testing in NHS diagnostic pathways for individuals presenting with auditory neuropathy or unexplained hearing loss, particularly when clinical features suggest a genetic aetiology.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
How is OTOF-related hearing loss inherited?
OTOF-related auditory neuropathy typically follows an autosomal recessive inheritance pattern, meaning an individual must inherit a pathogenic variant from both parents to develop the condition. Carriers with one variant generally have normal hearing.
Can OTOF testing help explain hearing loss in children?
Yes, OTOF testing is particularly useful when a child presents with auditory neuropathy or discordant audiological findings, such as preserved cochlear function but poor speech perception. Genetic diagnosis can guide management and inform family planning.
Are there treatments for OTOF-related auditory neuropathy?
Management strategies include cochlear implantation, which has shown benefit in many individuals with OTOF-related hearing loss by bypassing the impaired hair cell synapses and directly stimulating auditory nerve fibres. Early intervention and audiological support are important for optimising communication development.