PDE6C

At least 19 mutations in the PDE6C gene have been found to cause the vision disorder achromatopsia. These mutations underlie a relatively small percentage of cases of complete achromatopsia, a form of the disorder characterized by a total lack of color vision and other vision problems that are present from early infancy. PDE6C gene mutations have also been identified in a few individuals with incomplete achromatopsia, a milder form of the disorder associated with limited color vision.

The PDE6C gene mutations associated with achromatopsia affect the function of the alpha-prime subunit. The mutations that underlie complete achromatopsia essentially eliminate the activity of cone-specific phosphodiesterase. Impairment of this enzyme disrupts the process of phototransduction in cones; rods are typically unaffected. Because cones are needed for color vision, people with complete achromatopsia can see only black, white, and shades of gray. They also have other vision problems related to malfunctioning cones, including reduced sharpness (low visual acuity), an increased sensitivity to light (photophobia), and involuntary back-and-forth eye movements (nystagmus).

Mutations in the PDE6C gene that reduce but do not eliminate the activity of cone-specific phosphodiesterase cause incomplete achromatopsia. People with incomplete achromatopsia have similar but less severe vision problems than people with complete achromatopsia, and they retain some color vision.

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