Overview
TRPM1 encodes a cation channel expressed in the ON-bipolar cells of the retina. This channel is essential for the transmission of signals from photoreceptors to bipolar cells and thus for light perception. Mutations in TRPM1 lead to congenital stationary night blindness type 1C (CSNB1C), an autosomal recessive form of night blindness.
15q13.3 (Chromosome 15)
Hereditary Diseases
Autosomal recessive
Rare
Function & Significance
TRPM1 is a non-selective cation channel that is part of the signaling cascade in ON-bipolar cells. When light hits photoreceptors, glutamate release is reduced. This activates a G-protein cascade via the mGluR6 receptor (encoded by GRM6), which ultimately opens TRPM1 channels and depolarizes the bipolar cell.
In mutations in TRPM1, this signaling cascade is interrupted. The ON-bipolar cells cannot respond correctly to light, leading to night blindness. Day vision is often less impaired because OFF-bipolar cells (which use a different signaling pathway) function normally.
🔬 ON and OFF Bipolar Cells
The retina has two types of bipolar cells: ON-bipolar cells (depolarize in light) and OFF-bipolar cells (hyperpolarize in light). TRPM1 is only present in ON-bipolar cells. Therefore, TRPM1 mutations lead to a selective loss of the ON response, which is shown in the electroretinogram (ERG) as a missing b-wave.
Associated Diseases
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🌙 Congenital Stationary Night Blindness Type 1C (CSNB1C)
Night blindness from birth, normal or slightly reduced day vision, myopia
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👁️ Autosomal Recessive Night Blindness
Affects both sexes equally; two mutated copies required
🧬 Relevant SNPs
Various mutations in TRPM1 have been described, including missense, nonsense, frameshift, and splice-site mutations. Most are private mutations. There is no single common mutation.
⚕️ Clinical Significance
Diagnosis: Electroretinogram (ERG) shows missing b-wave, characteristic of CSNB1. Clinical examination shows night blindness, often with myopia. Genetic tests differentiate between TRPM1, GRM6, NYX, and other CSNB genes.
Management: No causal therapy available. Symptomatic treatment:
- Glasses/Contact Lenses: For myopia correction
- Lighting: Bright lighting at night
- Fitness to Drive: Night driving ban recommended
Prognose: Stationary, no worsening. Normal life expectancy. Day vision is usually sufficient for normal activities.
📚 Data Sources
The information on this page is based on the following scientific sources:
- OMIM: #613216 (Night Blindness, Congenital Stationary, Type 1C)
- ClinVar: Pathogenic TRPM1 variants
- PubMed: Literature on TRPM1 and night blindness
- Orphanet: ORPHA216816 (Autosomal recessive congenital stationary night blindness)
Last Update: February 2026