OPN1SW

The OPN1SW gene provides instructions for making a protein that is essential for normal color vision. This gene is active in the retina, a light-sensitive tissue at the back of the eye. The retina contains two types of light receptor cells called rods and cones. Rods are responsible for vision in low light. Cones provide vision in bright light, including color vision. Three types of cones each contain a special pigment (a photopigment) that is most sensitive to a particular wavelength of light.

The OPN1SW gene produces a photopigment that is more sensitive to light at the blue/violet end of the visible spectrum. Cones with this pigment are usually called short-wavelength-sensitive or S cones. In response to light at shorter wavelengths, the photopigment triggers a series of chemical reactions within an S cone cell. These reactions ultimately alter the cell's electrical charge, generating a signal that is transmitted to the brain. The brain combines input from all three types of cones to produce normal color vision.

color vision deficiency - caused by mutations in the OPN1SW gene

Three mutations in the OPN1SW gene have been identified in people with blue-yellow color vision deficiency. These mutations cause a rare vision defect that makes it difficult or impossible to distinguish between shades of blue and green. Each of the three known OPN1SW mutations changes a single protein building block (amino acid) in the short-wave-sensitive photopigment. One mutation replaces glycine with arginine at position 79 (written as Gly79Arg), another mutation replaces serine with proline at position 214 (Ser214Pro), and a third mutation replaces proline with serine at position 264 (Pro264Ser). All of these genetic changes inactivate the photopigment by disrupting its structure or stability. Researchers suggest that S cone cells with a nonfunctional photopigment die prematurely or cannot transmit visual signals to the brain. This loss of S cones impairs the perception of blue and leads to confusion between shades of blue and green.

When S cones are completely nonfunctional, the specific type of blue-yellow color vision deficiency that results is called tritanopia. A less severe blue-yellow color vision defect called tritanomaly occurs when S cones function abnormally.