CNGA3 (Cyclic Nucleotide Gated Channel Subunit Alpha 3)

Overview

CNGA3 encodes the alpha subunit of a cyclic nucleotide-gated ion channel specifically expressed in the cone photoreceptors of the retina. Together with CNGB3, it forms a functional channel essential for phototransduction. Mutations cause Achromatopsia Type 2.

📍 Chromosomal Position

2q11.2 (Chromosome 2)

🧬 Gene Category

Hereditary Diseases

🔬 Inheritance

Autosomal recessive

📊 Prevalence

Second most common form (~25% of achromatopsia cases)

Function & Significance

CNGA3 forms the pore-forming alpha subunit of the CNG channel in cones. This channel is crucial for converting light signals into electrical signals. When light hits the cones, cGMP levels drop, leading to the closure of CNG channels and triggering hyperpolarization.

When mutations occur in CNGA3, the channel cannot be formed correctly or is non-functional. This results in the cones being unable to respond to light, leading to complete color blindness and severely reduced visual acuity in daylight.

🔬 Channel Structure

The functional CNG channel in cones is a heterotetramer consisting of two CNGA3 and two CNGB3 subunits. Both subunits are essential for channel function, which is why mutations in either gene result in the same clinical picture.

Associated Diseases

👁️ Achromatopsia Type 2 (ACHM2)

Complete color blindness, photophobia, nystagmus, visual acuity typically 20/200 or worse
🌈 No Color Perception

Affected individuals see the world exclusively in grayscale
📉 Central Scotomas

Blind spots in the central field of vision due to cone dysfunction

🧬 Relevant SNPs

rs121918359
2:98394389

Allele 1

Allele 2

Significance: Arg277Cys (R277C) – Pathogenic missense mutation that severely impairs channel function. Homozygous carriers develop complete achromatopsia.

⚕️ Clinical Significance

Diagnosis usually occurs within the first year of life through ophthalmological examinations and electroretinography (ERG), which shows a missing or severely reduced cone response. Genetic tests confirm the diagnosis.

Management: Tinted glasses or contact lenses to reduce photophobia, low-vision aids for close work, and early intervention are important measures. Gene therapy approaches are being actively researched.

📚 Data Sources

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

OMIM: #600053 (CNGA3), #216900 (Achromatopsia 2)
dbSNP: rs121918359
ClinVar: Pathogenic CNGA3 variants
PubMed: Literature on achromatopsia and CNG channels
Orphanet: ORPHA88 (Achromatopsia)

Last update: February 2026

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CNGA3