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PCDH15
protocadherin related 15
PCDH15 is located on the long (q) arm of chromosome 10, at band 10q21.1. Arm ratio per GRCh38 - banding schematic.
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Overview
PCDH15 (protocadherin related 15) encodes a member of the cadherin superfamily, a group of calcium-dependent cell adhesion molecules. The protein is essential for establishing the structural links between stereocilia - the hair-like projections on sensory cells in the inner ear that detect sound and motion. These links, known as tip links, convert mechanical vibrations into electrical signals the brain can interpret.
Pathogenic variants in PCDH15 are a recognised cause of Usher syndrome type 1, characterised by profound congenital hearing loss, balance problems, and progressive retinal degeneration leading to vision loss. The gene may also cause non-syndromic hearing loss in some families. Understanding PCDH15 function has been important for research into the molecular basis of sensory perception.
What the gene does
Protocadherin-15 functions as a key structural component in mechanotransduction - the process by which sensory cells convert physical stimuli into electrical signals. In the cochlea of the inner ear, protocadherin-15 forms the lower portion of tip links connecting adjacent stereocilia. When sound waves cause stereocilia to bend, tension on these tip links opens ion channels, generating the electrical signal that the auditory nerve transmits to the brain.
The protein's eleven extracellular cadherin domains enable it to interact with other adhesion molecules, particularly cadherin-23, to form the tip link complex. Calcium ions bind between these domains, maintaining the structural integrity necessary for mechanotransduction. In photoreceptor cells of the retina, protocadherin-15 contributes to the formation of calyceal processes - structures that connect the inner and outer segments of these light-sensing cells. Disruption of these connections impairs photoreceptor function and survival, leading to progressive retinal degeneration.
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Chromosome location
PCDH15 is located on the long arm of chromosome 10 at position 21.1 (10q21.1). The gene spans a substantial genomic region and encodes multiple alternatively spliced transcript variants, allowing different isoforms of the protein to be produced in different tissues and developmental stages. The largest isoform comprises 1,955 amino acids, making protocadherin-15 one of the larger members of the cadherin family.
Protein structure
The protocadherin-15 protein is organised into a series of eleven extracellular cadherin repeat domains (Cadherin 1 through Cadherin 11), spanning amino acids 40-1259. Each cadherin domain adopts a characteristic fold that binds calcium ions, which are essential for maintaining the extended structure of the protein. These repeats enable protocadherin-15 to project from the cell surface and interact with partner molecules on neighbouring cells.
The protein contains a single transmembrane region that anchors it in the cell membrane, and a cytoplasmic tail that interacts with the cellular scaffolding inside sensory cells. Several disordered regions are present in the cytoplasmic portion (amino acids 1426-1446, 1601-1623, 1745-1766, and 1928-1955), which may provide flexibility for protein-protein interactions and regulatory modifications. The extensive extracellular structure allows protocadherin-15 to span the gap between adjacent stereocilia and form stable mechanical connections.
Key variants
Pathogenic variants in PCDH15 include missense changes, nonsense mutations, frameshift insertions and deletions, and splice-site alterations. Variants that disrupt the cadherin domains can impair calcium binding or protein-protein interactions necessary for tip link formation. The inheritance pattern and clinical severity depend on the specific variants involved - biallelic loss-of-function variants typically cause Usher syndrome type 1, whilst certain variant combinations may result in isolated hearing loss without retinal involvement.
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.1201C>T | p.Gln401Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Autosomal recessive nonsyndromic hearing loss 23 |
c.1303del | p.Asp435fs | Pathogenic/Likely pathogenic | ★★☆☆ | Usher syndrome type 1F |
c.1630dup | p.Ile544fs | Pathogenic/Likely pathogenic | ★★☆☆ | Autosomal recessive nonsyndromic hearing loss 23 |
c.1997+1del | - | Pathogenic/Likely pathogenic | ★★☆☆ | PCDH15-related disorder |
c.3270T>G | p.Tyr1090Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Usher syndrome type 1D |
c.3781dup | p.Glu1261fs | Pathogenic/Likely pathogenic | ★★☆☆ | Autosomal recessive nonsyndromic hearing loss 23 |
c.4201C>T | p.Gln1401Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Autosomal recessive nonsyndromic hearing loss 23 |
c.4671+1429_4671+1432dup | E1641fs, E1648fs | Pathogenic/Likely pathogenic | ★★☆☆ | Usher syndrome type 1F |
c.4382_4385dup | p.His1462fs | Pathogenic/Likely pathogenic | ★★☆☆ | Usher syndrome type 1F |
GRCh37/hg19 10q21.1(chr10:55962156-55978098)x1 | - | Pathogenic | ★☆☆☆ | not specified |
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
The primary condition associated with PCDH15 is Usher syndrome type 1, an autosomal recessive disorder characterised by profound congenital deafness, balance problems due to vestibular dysfunction, and progressive retinitis pigmentosa that leads to night blindness and tunnel vision, often beginning in adolescence. Individuals with Usher syndrome type 1 typically require cochlear implants or other assistive devices for communication and may experience progressive vision loss that affects independence in adulthood.
Some families carry PCDH15 variants that cause non-syndromic hearing loss without the retinal component, suggesting that certain genetic changes may selectively affect cochlear function whilst sparing photoreceptors. The phenotypic variability depends on the nature and location of the pathogenic variants.
- Usher syndrome type 1 Dedicated page coming soon
UK clinical status
PCDH15 is included on the NHS Genomic Medicine Service Monogenic hearing loss panel (green classification, version R67) and the Retinal disorders panel (green classification, version R32). Green classification indicates strong evidence supporting the gene-disease relationship, meaning PCDH15 testing is available through the NHS for individuals with clinical features of Usher syndrome or unexplained congenital hearing loss with a family history suggesting genetic causation.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What is the role of PCDH15 in hearing?
PCDH15 encodes a protein that forms part of the tip links connecting stereocilia in the inner ear. These links are essential for converting sound vibrations into electrical signals, and their disruption causes hearing loss.
How is PCDH15 related to vision problems?
In the retina, protocadherin-15 contributes to structures connecting parts of photoreceptor cells. When these connections are disrupted by pathogenic variants, photoreceptors gradually degenerate, leading to progressive vision loss.
Can PCDH15 variants cause hearing loss without affecting vision?
Yes, some PCDH15 variants cause isolated non-syndromic hearing loss without retinal involvement. The specific clinical outcome depends on the nature and location of the pathogenic variants inherited.