CNGA3

The CNGA3 gene provides instructions for making a protein that forms part of an ion channel. Ion channels are openings in the cell membrane that transport electrically charged atoms (ions) into and out of cells. Specifically, the CNGA3 protein is part of a family of proteins that form cyclic nucleotide-gated (CNG) channels. CNG channels are involved in transmitting information about vision and smell from sensory cells to the brain.

The CNGA3 protein forms one part (the alpha subunit) of a CNG channel that is necessary for normal vision. These channels are present in light receptor cells called cones. As part of the light-sensitive tissue at the back of the eye (the retina), cones provide vision in bright light, including color vision. Other light receptor cells in the retina, called rods, are responsible for vision in low light.

In cones, CNG channels remain open under dark conditions. Positively charged ions can flow into the cell through these open channels. In response to light, these channels close to stop the inward flow of ions. This change in ion transport alters the cone cell's electrical charge, which generates a signal that the brain interprets as vision.

color vision deficiency - caused by mutations in the CNGA3 gene

More than 50 mutations in the CNGA3 gene have been identified in individuals with color vision deficiency. These mutations typically cause complete achromatopsia, which is a loss of all color vision. Most of the reported mutations change a single protein building block (an amino acid) in the CNGA3 protein, which changes the structure of CNG channels made with this protein. The altered CNG channels cannot regulate the flow of ions into cones. As a result, these light receptor cells are unable to transmit visual signals to the brain. A loss of normal cone function causes a lack of color vision, reduced sharpness, and other vision problems associated with complete achromatopsia.

A few mutations in the CNGA3 gene cause incomplete achromatopsia, a condition that causes impaired color vision. These mutations likely allow partial function of CNG channels in cones. The partially functional cones can transmit some visual information to the brain, causing a form of color vision deficiency that is usually milder than complete achromatopsia.