Video: Asthma can be passed down in some families

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About 20 million Americans suffer from asthma, and it's getting even more prevalent. New evidence finds that for some families, hereditary plays a big role. 

Sisters Breanna and Janee Coleman have battled asthma since they were babies. Even then, their mother believed that it came from her side of the family. 

"I had it from my father and mine being so bad, I figured the gene was strong and that they probably have it too," said Shavon Coleman, Breanna and Janee's mother. 

That experience helped Shavon Coleman teach her daughters how to recognize triggers. For them, it's often stress and the weather. 

"If it's too hot I'm sick. If it's too cold, I'm sick. If it rains, I'm sick," said Shavon. 

Genetics experts like the University of Chicago's Carole Ober agree that genes can make some people more sensitive to those triggers. 

"Sixty percent of the susceptibility to asthma is due to the genes we inherit from our parents," said Dr. Carole Ober, genetics expert. 

And now, Ober's discovered the first asthma gene, thanks to the cooperation of a little known religious sect in South Dakota, called the Hutterites. 

They generally marry among themselves. And it's that restricted gene pool that made it a bit easier to locate the asthma gene. Since then, Ober's also found the same gene in the general population. That's important, because gene research can lead to new tests and new treatments. 

"So that we won't just be treating the symptoms of asthma, but actually treating the defects that cause it," said Ober. 

When asthma starts in childhood, symptoms usually come and go. In adult-onset asthma, the condition are more likely to be ongoing and may require daily medication.