Donning fuzzy wool sweaters and earmuffs? Check.

Sipping cocoa by a flickering fire? Been there.

With winter in full swing, the novelty of icicles and snowballs has probably worn off. Shoveling snow or scraping frost off your car probably makes basking in the July sun sound refreshingly sweaty.

The dog days of summer can’t come fast enough for the six percent of Americans with seasonal affective disorder, a condition that can lead to depression during the winter months when daylight hours are in short supply.

Now researchers say the problem could trace back to a genetic glitch in the eye in some people.

Writing in the Journal of Affective Disorders, the researchers describe study findings linking seasonal affective disorder to a mutation with a photo-pigment gene in the eye. The mutation doesn’t affect how these people see light, but could affect how the body responds to it. As a result, they may need a few more sunbeams than the average person.

Those possessing this genetic snafu are five times more likely to have seasonal affective disorder than people who don’t. But studies have also linked seasonal affective disorder to off-balance circadian rhythms and hormones such as serotonin.

While there’s no proven way to prevent the disorder, some people use therapeutic light boxes to cope with it.

Getting as much sunshine time as possible even during the winter probably can’t hurt either. After all, there’s nothing like the real thing.