Gene Mutation May Cause Some Cases of Seasonal Affective Disorder

Nov. 8 -- FRIDAY, Nov. 7 (HealthDay News) -- A mutated gene in the eye may account for some cases of seasonal affective disorder, that annual bout of "winter blues" experienced by an estimated 6 percent of the U.S. population as the days get shorter.

"SAD [seasonal affective disorder] is a kind of major depression that recurs every year right around the fall," said lead researcher Ignacio Provencio, an associate professor of biology at the University of Virginia. "By the spring and early summer, it goes away."

Provencio noted that the treatment for SAD is light therapy, which usually takes about two hours a day. "Exposing patients to bright light can actually get rid of some of these symptoms and allow patients to function normally during the winter," he said.

Since light is the treatment for SAD, Provencio's group speculated that people with the condition may be less sensitive to light. "They can overcome that insensitivity by increasing the amount of light they're exposed to," he noted.

But only 50 percent of SAD patients respond to light therapy, Provencio said. "So it could be that this mutation could allow a way of predicting patients that may be responsive to light therapy," he added.

For the study, published in the November online edition of the Journal of Affective Disorders, Provencio's team looked at genes in 220 people. One hundred thirty of the people had been diagnosed with SAD, and 90 had no history of SAD or any other depressive disorder.

The researchers found that seven people had two copies of the mutated gene thought to be involved in SAD. All seven were in the group that had been diagnosed with the depressive condition. The researchers concluded that someone with two copies of the mutation was five times more likely to develop SAD, compared with someone without the mutation, Provencio said.

The gene is called the melanopsin gene, and it produces a light-sensitive protein found in photoreceptors in the eye's retina. The protein is not involved with vision, but it is linked to non-visual responses, such as circadian rhythms, hormones, alertness and sleep, Provencio said.