(USA TODAY) -- Grant Schlager sounds like a typical Minnesota kid: He loves to play outside, no matter how cold it gets, and he's pretty excited that a slow-to-start snow season is finally underway.

But Grant, who turns 12 this week, has a problem: He is literally allergic to cold. It makes him break out in hives and could cause more serious reactions if he's not careful.

So that means he can't play in the cold for hours, the way many Minnesota kids do. "After 15 minutes, my dad or mom will check me to see if I have any bumps," the fifth-grader says. If he is breaking out or feeling itchy, he has to go inside for a while. Swimming in cold water is risky, and so is drinking an icy soda. Just to be safe, he takes a twice-daily antihistamine and stays close to an EpiPen (a dose of epinephrine) -- the same stuff kids with peanut and bee-sting allergies need to inject if they have a life-threatening reaction.

Really? That was exactly the question his mother asked when he was diagnosed with the condition, called cold urticaria, at the Mayo Clinic in Rochester. "I had never heard of it and I was skeptical," says Amy Schlager, a mother of five from Jackson, Minn. "How can anybody be allergic to cold?"

Researchers are not sure, though a new study hints at some answers. They also don't know how common the problem is. One 1996 study from central Europe found about one in 2,000 people were affected in one year, says Joshua Milner, a researcher at the National Institute of Allergy and Infectious Diseases. He suspects the condition is more common.

Milner led the new study, published online by the New England Journal of Medicine. He and colleagues found a genetic mutation in 27 people from three families who all had cold urticaria mixed with other immune system abnormalities and disorders.

Right now, he says, no one knows how many people with cold urticaria have the mutation or some other underlying condition.

Martha Hartz, a pediatric allergist and immunologist at Mayo, says most cold urticaria patients she sees are like Grant: They don't test positive for any other known disorder. But that doesn't mean their condition isn't serious.

Hartz says she knows of one toddler who suffered anaphylaxis, a severe, life-threatening allergic reaction, after jumping into a cold wading pool on a warm day. As a result, the child has permanent brain damage, she says. That's the only such severe case she has encountered in 25 years, "but that is the risk," she says, for anyone with the condition.

Hartz and Milner say that's why it's important for people who think they might be allergic to cold to check with a doctor.

"People tend to think it's so weird that they are too bashful to tell their doctors about it," Milner says. "Sometimes they tell their doctors and are told they are out of their minds. Or they are tested for 8 million food allergies they don't have."

There is a test for cold urticaria: A doctor puts a melting ice cube on the patient's skin, then removes it and waits a few minutes to see whether hives begin. Some true sufferers will fail that test, though, Milner says. Hartz says some patients react on some parts of the body but not others.

Hartz says she diagnoses about two children a year with the condition and often has to call their schools to convince them cold allergy is real -- not just an excuse to get out of recess on a cold day.

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