Cystic Fibrosis Doesn't Stop Sisters From Bringing "America's Got Talent" Audience to Tears

NEW YORK (CBS) A pair of sisters with cystic fibrosis performed on "America's Got Talent" Wednesday night, bringing members of the audience to their feet - and to tears.

Ali, 20, and Christina, 13, sang Miley Cyrus' "The Climb" on the talent show, where they received praise from the judges and were chosen to go on to Las Vegas.

The sisters explained in the video before their performance that all four children in their family suffer from the genetic disease.

"It gets worse with age - your lungs can get really right. It's pretty hard," Ali explained, adding that the average life expectancy for those with the disease is mid-to-late 30s.

"But we can enjoy every minute together that we have," she continued. "If we pursue our dreams then it will give us something to look forward to instead of dwelling on our disease."

After their performance, which earned a standing ovation, Ali tearfully told the judges that the sisters had always been told they would never be able to sing because of their disease.

"Well you proved them wrong, haven't you?" Sharon Osbourne responded from the judges' table.

Howie Mandel told the girls they are "so inspirational."

"You have amazing talent, but that combined with what we know--it's just so moving. And I want for you anything you want in life, I really do," he continued.

If people know someone who has that terrible disease, it's an amazing thing that you're doing just by walking out and singing," Piers Morgan said.

The head judge also acknowledged that the sisters did enter a talent competition, and he'd have to judge them. He said they weren't the best singers that had appeared on the program, but that they sang with sincerity.

"I believed every word you were singing," he told them.

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