CNGB3 (Cyclic Nucleotide Gated Channel Subunit Beta 3)

Overview

CNGB3 encodes the beta subunit of a cyclic nucleotide-gated ion channel in the cone photoreceptors of the retina. This channel is essential for converting light signals into electrical signals. Mutations lead to Achromatopsia Type 3, the most common form of complete color blindness.

📍 Chromosomal Position

8q21.3 (Chromosome 8)

🧬 Gene Category

Hereditary Diseases

🔬 Inheritance

Autosomal recessive

📊 Prevalence

Most common form (~50% of all achromatopsia cases)

Function & Significance

The CNGB3 channel opens in response to cyclic GMP (cGMP), which is produced in the cones in response to light. When the channel opens, sodium and calcium ions flow into the cell, leading to depolarization and ultimately to signal transmission.

When mutations occur in CNGB3, this channel is defective or missing entirely. While the cones can absorb light, the signal is not converted into an electrical impulse. This leads to complete cone dysfunction, whereas the rods (used for night vision) function normally.

🔬 Cones vs. Rods

The retina contains two types of photoreceptors: cones (for color vision and daylight) and rods (for night vision). In achromatopsia, only the cones are affected, which is why those affected often see better in the dark than in bright light.

Associated Diseases

👁️ Achromatopsia Type 3 (ACHM3)

Complete color blindness, photophobia, nystagmus, severely reduced visual acuity (typically 20/200)
☀️ Extreme Photosensitivity

Affected individuals often require very dark glasses outdoors
👶 Congenital Nystagmus

Involuntary eye movements appearing as early as infancy

🧬 Relevant SNPs

rs121918361
8:87653579

Allele 1

Allele 2

Significance: Thr383Ile (T383I) – Common pathogenic variant that impairs channel function. Homozygous genotype (TT) leads to complete achromatopsia.

⚕️ Clinical Significance

Achromatopsia is usually diagnosed in the first months of life when parents notice the child is extremely sensitive to light and exhibits involuntary eye movements. Early diagnosis is important for support and adaptation.

Current Research: Gene therapy trials for CNGB3 achromatopsia are already in clinical phases. Initial results show promising improvements in visual function.

📚 Data Sources

The information on this page is based on the following scientific sources:

OMIM: #605080 (CNGB3), #262300 (Achromatopsia 3)
dbSNP: rs121918361
ClinVar: Pathogenic CNGB3 variants
PubMed: Literature on achromatopsia and gene therapy
Orphanet: ORPHA88 (Achromatopsia)

Last update: February 2026

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CNGB3