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.

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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.

McCune Albright syndrome is an unusual type of disease with varied symptoms. In this disease, a mutation occurs sometime after conception, affecting only some of the body's cells. The number and type of symptoms depend on which cells—and thus which organs—are affected.

Scientists have found that the mutation affects the gene that codes for he same G-protein involved in cholera. This G-protein gets stuck in the "on" position. In skin cells, this causes darker than normal pigment. If the mutation affects bone cells, it causes weakness and fractures. In hormone-producing cells, the mutation causes the release of excess hormones.

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McCune Albright syndrome

Skin cells and bone cells are affected in this 4-year-old girl with McCune Albright syndrome. She wears a body cast because of bone fractures. The mosaic pattern of darkened skin is visible.