GPR98 Gene

GPR98 Gene

Gene Overview

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">GPR98 Gene</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td>GPR98</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>G Protein-Coupled Receptor 98 (VLGR1)</td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>5q14.3</td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td>[84059](https://www.ncbi.nlm.nih.gov/gene/84059)</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>[602851](https://www.omim.org/entry/602851)</td>
</tr>
<tr>
<td class="label">Ensembl</td>
<td>[ENSG00000138297](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000138297)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td>[Q8WXF3](https://www.uniprot.org/uniprot/Q8WXF3)</td>
</tr>
<tr>
<td class="label">Partner Protein</td>
<td>Interaction Type</td>
</tr>
<tr>
<td class="label">USH1C (harmonin)</td>
<td>Direct binding</td>
</tr>
<tr>
<td class="label">CDH23</td>
<td>Complex formation</td>
</tr>
<tr>
<td class="label">MYO7A</td>
<td>Co-localization</td>
</tr>
<tr>
<td class="label">PCDH15</td>
<td>Heterodimer</td>
</tr>
<tr>
<td class="label">WHRN (whirlin)</td>
<td>Scaffold interaction</td>
</tr>
<tr>
<td class="label">Trial ID</td>
<td>Phase</td>
</tr>
<tr>
<td class="label">NCT01505062</td>
<td>I/II</td>
</tr>
<tr>
<td class="label">NCT02898012</td>

GPR98 Gene

Gene Overview

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">GPR98 Gene</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td>GPR98</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>G Protein-Coupled Receptor 98 (VLGR1)</td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>5q14.3</td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td>[84059](https://www.ncbi.nlm.nih.gov/gene/84059)</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>[602851](https://www.omim.org/entry/602851)</td>
</tr>
<tr>
<td class="label">Ensembl</td>
<td>[ENSG00000138297](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000138297)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td>[Q8WXF3](https://www.uniprot.org/uniprot/Q8WXF3)</td>
</tr>
<tr>
<td class="label">Partner Protein</td>
<td>Interaction Type</td>
</tr>
<tr>
<td class="label">USH1C (harmonin)</td>
<td>Direct binding</td>
</tr>
<tr>
<td class="label">CDH23</td>
<td>Complex formation</td>
</tr>
<tr>
<td class="label">MYO7A</td>
<td>Co-localization</td>
</tr>
<tr>
<td class="label">PCDH15</td>
<td>Heterodimer</td>
</tr>
<tr>
<td class="label">WHRN (whirlin)</td>
<td>Scaffold interaction</td>
</tr>
<tr>
<td class="label">Trial ID</td>
<td>Phase</td>
</tr>
<tr>
<td class="label">NCT01505062</td>
<td>I/II</td>
</tr>
<tr>
<td class="label">NCT02898012</td>
<td>I</td>
</tr>
<tr>
<td class="label">NCT03780109</td>
<td>I</td>
</tr>
<tr>
<td class="label">Feature</td>
<td>USH2A (VLGR1)</td>
</tr>
<tr>
<td class="label">Hearing</td>
<td>Moderate-Severe</td>
</tr>
<tr>
<td class="label">Vestibular</td>
<td>Normal</td>
</tr>
<tr>
<td class="label">Retinitis</td>
<td>Post-adolescent</td>
</tr>
<tr>
<td class="label">Onset</td>
<td>Adolescence</td>
</tr>
</table>

{{.infobox .infobox-gene}}

Associated Diseases

Function

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](https://pubmed.ncbi.nlm.nih.gov/12496658/).

Molecular Function

The VLGR1 protein contains:

• extracellular calcium-binding domains (CalX-beta motifs)
• 7 transmembrane domains characteristic of GPCRs
• Large intracellular loop for protein interactions
• C-terminal PDZ-binding motif for scaffolding protein interactions

Role in the Brain

Beyond the inner ear, GPR98 is expressed in various brain regions including:

• Cerebellum - Purkinje cells and granule cells
• [Hippocampus](/brain-regions/hippocampus) - CA1-CA3 regions
• [Cortex](/brain-regions/cortex) - Layer 5 pyramidal [neurons](/entities/neurons)
• Thalamus - Relay neurons

Expression

Tissue Distribution

GPR98 shows high expression in:

• Inner ear: Sensory hair cells of cochlea and vestibular system
• Brain: Cerebellum, hippocampus, cortex
• Retina: Photoreceptor cells
• Testis: Developing sperm cells
• Kidney: Epithelial cells

Developmental Expression

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.

Clinical Significance

Usher Syndrome Type 2A

Mutations in GPR98 cause Usher syndrome type 2A, characterized by:

• Moderate to severe sensorineural hearing loss (present from birth)
• Normal vestibular function (unlike USH1C)
• Progressive retinitis pigmentosa (typically beginning in adolescence)

Febrile Seizures

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](https://pubmed.ncbi.nlm.nih.gov/17336073/).

Neurodegeneration Connections

Auditory Neurodegeneration

GPR98 dysfunction leads to progressive hearing loss, representing a form of sensory neuron degeneration. Understanding the mechanisms of stereocilia degeneration may provide insights into:

Neuronal Implications

While primarily studied in the context of Usher syndrome, GPR98's expression in the brain suggests broader neurological functions:

• Synaptic plasticity: GPCR signaling is fundamental to synaptic function
• Calcium homeostasis: The calcium-binding domains suggest role in calcium regulation
• Neuronal development: May guide axonal growth and targeting

Key Publications

See Also

• [Usher syndrome](/diseases/usher-syndrome)
• [Hair cell proteins](/categories/hair-cells)
• [GPCR signaling](/categories/gpcr-proteins)
• [Sensory genes](/categories/sensory-genes)
• [Hearing loss](/diseases/sensorineural-hearing-loss)

External Links

• [NCBI Gene: GPR98](https://www.ncbi.nlm.nih.gov/gene/84059)
• [UniProt: Q8WXF3](https://www.uniprot.org/uniprot/Q8WXF3)
• [Ensembl: ENSG00000138297](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000138297)
• [OMIM: 602851](https://www.omim.org/entry/602851)

Protein Structure

Domain Organization

VLGR1/GPR98 has a unique architecture:

[@nterminal]: N-terminal signal peptide (1-20 aa)
[@calxbeta]: CalX-beta motifs (21-3500 aa): Calcium-binding domains
[@epidermal]: Epidermal growth factor-like domains (3500-4500 aa)
[@transmembrane]: 7 transmembrane domains (4500-5200 aa)
[@cterminal]: C-terminal PDZ-binding motif (6200 aa)

The CalX-beta domains are unique among GPCRs and may function as calcium sensors.

Post-Translational Modifications

• N-glycosylation: Multiple sites in extracellular domain
• Disulfide bonds: Important for domain folding
• Palmitoylation: Membrane association

Signaling Mechanisms

GPCR Signaling

Despite its large size, VLGR1 is a functional GPCR:

• G protein coupling: Primarily couples to Gi/o family
• Calcium signaling: Modulates intracellular calcium
• cAMP regulation: Through Gs coupling in some contexts

Non-GPCR Functions

• Cell adhesion: Through extracellular domain interactions
• Guidance molecule: Directs stereocilia development

Animal Models

Knockout Mouse

• Phenotype: Hearing loss, vestibular dysfunction
• Stereocilia: Abnormal organization, eventual degeneration
• Retina: Progressive photoreceptor loss
• Study utility: Therapeutic testing platform

Zebrafish

• Morphants: Hair cell defects
• Transgenics: Visualize protein localization

Therapeutic Approaches

Gene Therapy

• AAV delivery: Challenges due to large gene size
• Lentiviral vectors: Alternative for large genes
• Non-viral methods: Under development

Pharmacological

Pharmacological approaches for GPR98-related disorders are limited due to the large protein size and blood-labyrinth barrier:

• Inner ear drug delivery: Novel approaches including intratympanic injection and osmotic pumps
• Otic nanoparticles: Targeted delivery systems under development
• Small molecule approaches: Focus on downstream effectors rather than GPR98 itself

Neurodegeneration Connections

Auditory Neurodegeneration

GPR98 dysfunction leads to progressive hearing loss, representing a form of sensory neuron degeneration. Understanding the mechanisms of stereocilia degeneration may provide insights into:

Neuronal Implications

While primarily studied in the context of Usher syndrome, GPR98's expression in the brain suggests broader neurological functions:

• Synaptic plasticity: GPCR signaling is fundamental to synaptic function
• Calcium homeostasis: The calcium-binding domains suggest role in calcium regulation
• Neuronal development: May guide axonal growth and targeting

Neuroinflammation and GPR98

Emerging evidence suggests GPR98 may play a role in neuroinflammation:

Protein Interactions and Signaling

Key Protein Interactors

GPR98 interacts with several key proteins involved in sensory system function:

Downstream Signaling Pathways

Despite being one of the largest GPCRs, GPR98 engages multiple signaling cascades:

GPCR Signaling Dysfunction in Disease

When GPR98 function is impaired, downstream signaling is affected:

• Disrupted mechanotransduction: Failure of hair cell response to sound
• Impaired calcium regulation: Cellular homeostasis disruption
• Altered cellular adhesion: Stereocilia organization defects
• Apoptotic susceptibility: Increased cell death in sensory cells

Clinical Research and Trials

Gene Therapy Trials

Several clinical trials are investigating gene therapy approaches for Usher syndrome:

Biomarker Development

GPR98 expression levels may serve as biomarkers:

• Diagnostic markers: GPR98 mutations in Usher syndrome
• Progression markers: Correlation with hearing/visual loss
• Therapeutic response: Gene therapy effectiveness

Pharmacological Trials

Current pharmacological approaches focus on:

Animal Models and Research

Knockout Mouse Phenotypes

The GPR98 knockout mouse provides critical insights:

• Complete knockout: Embryonic lethal in some backgrounds
• Conditional knockouts: Tissue-specific deletion reveals function
• Phenotype characteristics: Deafness, vestibular dysfunction, retinal degeneration

Comparative Biology

Studying GPR98 across species reveals:

• Zebrafish: Ortholog essential for hair cell development
• Xenopus: Model for cilia-mediated mechanotransduction
• Canine: Spontaneous USH2A mutations in certain breeds

Cellular and Molecular Mechanisms

Mechanotransduction Complex

GPR98 participates in the hair cell mechanotransduction apparatus:

Calcium-Dependent Regulation

The CalX-beta domains provide calcium-dependent regulation:

Protein Quality Control

GPR98 undergoes rigorous quality control:

• ER folding: Chaperone-assisted maturation
• Trafficking: Golgi processing and sorting
• Degradation: ER-associated degradation for misfolded protein
• Surface expression: Proper membrane insertion

Therapeutic Challenges and Future Directions

Delivery Challenges

The large size of GPR98 presents unique challenges:

Combination Therapies

Future approaches may combine multiple strategies:

• Gene therapy plus pharmacological: Enhance transduction efficiency
• Cell therapy plus gene therapy: Stem cell approaches
• Biomarker-guided therapy: Personalized medicine approaches

Emerging Technologies

Novel technologies may overcome current limitations:

• Split-intein AAV: Larger gene delivery systems
• Base editing: Single nucleotide corrections
• Nanoparticle delivery: Non-viral gene transfer

Differential Diagnosis

USH2 vs Other Usher Syndrome Types

Research Directions

Current Focus

• Gene therapy: Overcoming size limitations
• Mechanism studies: Understanding normal function
• Biomarkers: Early detection and progression tracking

Challenges

• Large gene size limits delivery
• Progressive nature requires early intervention
• Retinal delivery remains challenging

References