{{.infobox .infobox-gene}}
| Symbol | GPR98 |
| Full Name | G Protein-Coupled Receptor 98 (VLGR1) |
| Chromosome | 5q14.3 |
| NCBI Gene | 84059 |
| OMIM | 602851 |
| Ensembl | ENSG00000138297 |
| UniProt | Q8WXF3 |
Usher syndrome type 2A, Febrile seizures, Familial febrile seizures
GPR98 (also known as VLGR1 - Very Large G-Protein Coupled Receptor 1) encodes one of the largest known G-protein coupled receptors, with over 6000 amino acids. This massive receptor plays critical roles in the development and maintenance of stereocilia in inner ear hair cells and in neuronal development 1.
The VLGR1 protein contains:
VLGR1 localizes to the ankle links of hair cell stereocilia during development, where it functions as a guidance molecule for the organization of the stereocilia bundle. It interacts with other Usher syndrome proteins including USH1C (harmonin), CDH23, and MYO7A 2.
Beyond the inner ear, GPR98 is expressed in various brain regions including:
The receptor is thought to play roles in neuronal migration, synaptic plasticity, and neurotransmission, though the exact mechanisms remain under investigation.
GPR98 shows high expression in:
Expression begins during embryonic development (around week 8 in humans) and increases through fetal development, peaking in the early postnatal period when stereocilia maturation occurs.
Mutations in GPR98 cause Usher syndrome type 2A, characterized by:
GPR98 mutations have been associated with febrile seizures, suggesting a role in neuronal excitability. The mechanism may involve altered calcium signaling or synaptic transmission in response to fever 3.
GPR98 dysfunction leads to progressive hearing loss, representing a form of sensory neuron degeneration. Understanding the mechanisms of stereocilia degeneration may provide insights into:
While primarily studied in the context of Usher syndrome, GPR98's expression in the brain suggests broader neurological functions:
VLGR1/GPR98 has a unique architecture:
The CalX-beta domains are unique among GPCRs and may function as calcium sensors.
Despite its large size, VLGR1 is a functional GPCR:
Pharmacological approaches for GPR98-related disorders are limited due to the large protein size and blood-labyrinth barrier:
GPR98 dysfunction leads to progressive hearing loss, representing a form of sensory neuron degeneration. Understanding the mechanisms of stereocilia degeneration may provide insights into:
While primarily studied in the context of Usher syndrome, GPR98's expression in the brain suggests broader neurological functions:
Emerging evidence suggests GPR98 may play a role in neuroinflammation:
GPR98 interacts with several key proteins involved in sensory system function:
| Partner Protein | Interaction Type | Functional Outcome |
|---|---|---|
| USH1C (harmonin) | Direct binding | Stereocilia organization |
| CDH23 | Complex formation | Tip link formation |
| MYO7A | Co-localization | Motor protein transport |
| PCDH15 | Heterodimer | Mechanotransduction |
| WHRN (whirlin) | Scaffold interaction | Stereocilia elongation |
Despite being one of the largest GPCRs, GPR98 engages multiple signaling cascades:
When GPR98 function is impaired, downstream signaling is affected:
Several clinical trials are investigating gene therapy approaches for Usher syndrome:
| Trial ID | Phase | Approach | Status |
|---|---|---|---|
| NCT01505062 | I/II | AAV-GPR98 | Completed |
| NCT02898012 | I | Lentiviral-USH2A | Recruiting |
| NCT03780109 | I | AAV-MYO7A | Active |
GPR98 expression levels may serve as biomarkers:
Current pharmacological approaches focus on:
The GPR98 knockout mouse provides critical insights:
Studying GPR98 across species reveals:
GPR98 participates in the hair cell mechanotransduction apparatus:
The CalX-beta domains provide calcium-dependent regulation:
GPR98 undergoes rigorous quality control:
The large size of GPR98 presents unique challenges:
Future approaches may combine multiple strategies:
Novel technologies may overcome current limitations:
| Feature | USH2A (VLGR1) | USH1 | USH3 |
|---|---|---|---|
| Hearing | Moderate-Severe | Profound | Progressive |
| Vestibular | Normal | Abnormal | Variable |
| Retinitis | Post-adolescent | Early | Variable |
| Onset | Adolescence | Congenital | Adolescence |