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Scientists have found a G-protein defect in one type of inherited night blindness. Persons with this condition have a mutation in the gene that codes for the G-protein found in the eye's rod cells. Scientists believe that this defective G-protein is overactive. It stays turned on more than it normally would, and the person can't see well at low light levels.

During the day, a similar system in the cone cells of the eyes allows us to see color. This system depends on a different G-protein. Thus, persons with night blindness have normal daytime vision.

Light enters the eye (1) and strikes the rod cells in the retina
(2). Light receptors, G-proteins and amplifiers are on discs within
the rods (3)

When light strikes a light receptor, it activates a G-protein, which binds to an amplifier molecule. This sends a signal to the brain, resulting in light perception. G-proteins normally turn themselves off in a natural regulatory cycle. But in inherited night blindness, the G-protein stays on, interfering with normal vision.
Image: Courtesy of NIDDK
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