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TMC1
transmembrane channel like 1
TMC1 is located on the long (q) arm of chromosome 9, at band 9q21.13. Arm ratio per GRCh38 - banding schematic.
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Overview
TMC1 (transmembrane channel like 1) is located on chromosome 9 at band 9q21.13 and encodes a 760-amino-acid protein integral to the mechanotransduction machinery of cochlear hair cells. These specialised sensory cells convert sound vibrations into electrical signals that the brain interprets as hearing. When TMC1 carries pathogenic variants, the resulting protein dysfunction disrupts this conversion process, leading to progressive or congenital hearing impairment. The gene is included in NHS clinical panels for monogenic hearing loss, reflecting its established role in diagnosis and genetic counselling for families affected by inherited deafness.
What the gene does
The TMC1 protein is thought to function as a component of mechanosensitive ion channels in the stereocilia of cochlear hair cells. Stereocilia are tiny hair-like projections that bend in response to sound waves, opening channels that allow ions to flow into the cell and generate electrical signals. Evidence suggests that TMC1 forms part of the channel complex responsible for this critical mechanotransduction step, enabling the transformation of mechanical stimuli into neural impulses. The protein's precise arrangement within the channel complex and its interaction with other structural proteins remain active areas of investigation. Loss of functional TMC1 impairs the hair cells' ability to respond appropriately to sound, resulting in diminished or absent hearing. Different variants may affect channel properties in distinct ways, accounting for the variability in severity and progression observed in affected individuals.
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Chromosome location
TMC1 is situated on the long arm of chromosome 9 at cytogenetic band 9q21.13. This region lies roughly midway along the chromosome's length. The genomic span and exon architecture of TMC1 have been catalogued, with the gene comprising multiple exons that are transcribed and spliced to produce the mature messenger RNA template for the protein.
Protein structure
The TMC1 protein consists of 760 amino acids and is predicted to contain multiple transmembrane segments consistent with its proposed role as an ion channel component. Structural modelling indicates an N-terminal region spanning approximately amino acids 1 to 80 that is disordered, lacking a stable three-dimensional fold under physiological conditions. Disordered regions often serve regulatory or protein-interaction functions rather than contributing to the core channel architecture. The remainder of the protein is thought to include transmembrane helices that anchor TMC1 in the cell membrane and form part of the ion-conducting pathway, though high-resolution experimental structures are not yet available for the full-length human protein.
Key variants
Pathogenic variants in TMC1 have been documented across the gene's coding sequence, with different mutations causing either autosomal recessive or autosomal dominant forms of hearing loss. Recessive variants typically result in complete loss of protein function, whilst certain dominant variants may exert dominant-negative effects or alter channel properties in ways that disrupt normal hearing even when one functional copy remains. The spectrum of reported variants includes missense changes, frameshifts, and splice-site alterations, each with differing impacts on protein structure and channel activity.
No pathogenic or likely-pathogenic ClinVar variants recorded yet for this gene.
Associated conditions
Variants in TMC1 are primarily associated with non-syndromic sensorineural hearing loss, meaning the hearing impairment occurs in isolation without other systemic features. Both congenital deafness present from birth and progressive hearing loss developing in childhood or adolescence have been linked to TMC1 dysfunction. The mode of inheritance and specific variant involved influence the age of onset, severity, and rate of progression. Families with a history of early-onset or progressive deafness may benefit from genetic testing that includes TMC1, particularly when other common causes have been excluded.
No disease links recorded for this gene in our reference set.
UK clinical status
TMC1 is listed on the NHS Genomic Medicine Service PanelApp as a green (high-evidence) gene in the Monogenic Hearing Loss panel, version R67. This classification indicates strong evidence supporting the gene's role in inherited hearing impairment and its inclusion in diagnostic testing pathways. Clinicians may request genetic testing for TMC1 variants through NHS genomic services when the clinical presentation and family history suggest an inherited cause of deafness.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What type of hearing loss do TMC1 variants cause?
TMC1 variants typically cause sensorineural hearing loss, which arises from dysfunction of the inner ear's sensory cells rather than problems with sound conduction through the outer or middle ear. The severity and progression vary depending on the specific variant and inheritance pattern.
Can TMC1-related hearing loss be inherited in different ways?
Yes, TMC1-associated hearing loss can follow either autosomal recessive or autosomal dominant inheritance, depending on the variant. Recessive forms generally require two altered copies, whilst dominant forms can cause hearing impairment with just one pathogenic variant.
Is genetic testing for TMC1 available on the NHS?
TMC1 is included in the NHS Genomic Medicine Service panel for monogenic hearing loss. Eligibility for testing depends on clinical criteria and family history, and referrals are typically made by specialists such as audiologists or clinical geneticists.