OPN1MW — Opsin 1, Medium-Wave-Sensitive

Illustration of the eye cross-section showing the retina at the back of the eye

The OPN1MW gene is responsible for making a protein in your eyes that helps you see the colors yellow and green. This protein is located in special cells in the retina called cones, which are essential for color vision in bright light. When there are mutations or changes in the OPN1MW gene, it can lead to color vision deficiencies, most commonly red-green color blindness. This makes it difficult or impossible to distinguish between shades of red, yellow, and green. In more severe but rarer cases, such as blue cone monochromacy, mutations can lead to poor visual acuity, sensitivity to light, and an inability to perceive most colors.

Gene description: The OPN1MW gene provides instructions for making an opsin pigment that is more sensitive to light in the middle of the visible spectrum (yellow/green light). This protein is essential for normal color vision and is found in the retina's cone photoreceptor cells.

Patient and family guide: The OPN1MW gene is responsible for making a protein in your eyes that helps you see the colors yellow and green. This protein is located in special cells in the retina called cones, which are essential for color vision in bright light. When there are mutations or changes in the OPN1MW gene, it can lead to color vision deficiencies, most commonly red-green color blindness. This makes it difficult or impossible to distinguish between shades of red, yellow, and green. In more severe but rarer cases, such as blue cone monochromacy, mutations can lead to poor visual acuity, sensitivity to light, and an inability to perceive most colors.

Gene function: OPN1MW encodes the medium-wave-sensitive opsin 1 visual pigment, a G-protein-coupled receptor that absorbs light in cone photoreceptors. It selectively activates G(i) proteins in response to medium-wavelength (green) light, thereby decreasing intracellular cAMP levels and triggering a phototransduction cascade.

Protein structure: The protein is a G-protein-coupled receptor with a 7-transmembrane helix structure. It consists of 364 amino acids and functions as a monomer, homodimer, or homotetramer.

Molecular function: OPN1MW functions as a G protein-coupled photoreceptor that selectively activates G(i) proteins in response to medium-wavelength (green) light near 530 nm. Activation occurs when the opsin-bound cis-retinal chromophore absorbs a photon and isomerizes to all-trans-retinal. This induces a conformational change in the opsin that triggers a G protein-mediated phototransduction cascade, decreasing intracellular cAMP levels and mediating visual perception of green light.

Mutation spectrum: Mutations include structural rearrangements (deletions or duplications) involving the OPN1LW and OPN1MW genes due to unequal recombination, leading to hybrid pigment genes. Missense mutations (e.g., Cys203Arg) and deletions of the locus control region (LCR) are also found.

Clinical significance: Mutations in the OPN1MW gene cause red-green color vision defects (deuteranopia or deuteranomaly) by altering or eliminating the function of the medium-wave-sensitive photopigment. Severe mutations, often involving both OPN1LW and OPN1MW or their regulatory region, cause blue cone monochromacy, characterized by severely reduced visual acuity and loss of color vision.

Inheritance: X-Linked

Chromosomal location: Xq28

Research and therapeutic approaches: Currently, there are no approved cures, but AAV-mediated gene augmentation therapy is being actively researched. Preclinical studies in animal models have shown that gene therapy can successfully restore M-cone structure and function, and clinical trials for blue cone monochromacy are advancing.