GNAT2

Achromatopsia

At least 10 mutations in the GNAT2 gene have been found to cause the vision disorder achromatopsia. These mutations are a relatively uncommon cause 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. GNAT2 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 GNAT2 gene mutations that underlie complete achromatopsia lead to an abnormally small, nonfunctional version of the cone-specific alpha subunit of transducin. Without this subunit, cones have no functional transducin, and

they are unable to carry out phototransduction. (The subunit produced from the GNAT2 gene is specific to cones, so rods are typically unaffected by this disorder.) A loss of cone function underlies the lack of color vision and other vision problems in people with complete achromatopsia.

At least one known GNAT2 gene mutation causes incomplete achromatopsia. The mutation, which is written as c.461+2G>A, affects the way the gene's instructions are pieced together to form the subunit protein. This mutation allows the production of some functional cone-specific alpha subunit, although the amount of the subunit is greatly reduced. As a result, a small amount of functional transducin is available to play its role in phototransduction, and the partially functioning cones can transmit some visual information to the brain.