Seasonal affective disorder may be linked to genetic mutation, stud...( With the days shortening toward wint...)

With the days shortening toward winter, many people will begin to experience the winter blahs. For some, the effect can be devastating.

About 6 percent of the U.S. population suffers from seasonal affective disorder, or SAD, a sometimes-debilitating depression that begins in the fall and continues through winter. Sufferers may even find it difficult to get out of bed in the morning.

The disorder, which is not well understood, is often treated with "light therapy," where a SAD patient spends time each morning before a bank of bright lights in an effort to trick the brain into believing that the days are not so short or dim.

A new study indicates that SAD may be linked to a genetic mutation in the eye that makes a SAD patient less sensitive to light.

"These individuals may require brighter light levels to maintain normal functioning during the winter months," said Ignacio Provencio, a University of Virginia biology professor who studies the genetics of the body's biological clock, or circadian rhythms.

Provencio and his colleagues have discovered that melanopsin, a photopigment gene in the eye, may play a role in causing SAD for people with a recently discovered mutation.

"We believe that the mutation could contribute to increasing the amount of light needed for normal functioning during winter for people with SAD," Provencio said. "Lack of adequate light may be a trigger for SAD, but not the only explanation for the disorder."

The findings are published in the online edition of the Journal of Affective Disorders, and will appear later in the print version.

The study was conducted with several other institutions, including the National Institute of Mental Health, and involved 220 participants 130 of whom had been diagnosed with SAD, and 90 participants with no history of mental illness.

Using a genetics test, the study authors found that seven of the 220 participants carried
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