It all started at a soccer game.
"I noticed she was running differently and falling a lot," said Skriver's mom, Tammy Skriver, a single mother of two in Central Florida. "When we got home I said, 'Show mommy how you skip' -- she loved to skip -- and she couldn't do it."
Skriver became increasingly lethargic, and soon began drooling and wetting the bed. Within a year, she could no longer walk. And by age 9, she needed a feeding tube. But countless blood tests, biopsies, brain scans and spinal taps have failed to uncover the cause of her ever-worsening condition.
"Doctors say it's a neurodegenerative disorder, but they don't know what it is or why it's happening," said Tammy Skriver, talking through tears. "It's excruciating. I get down on my knees all the time and just pray this is a dream."
Skriver is one of 550 patients in the Undiagnosed Diseases Program, a branch of the National Institutes of Health that aims to diagnose and cure the country's most puzzling patients.
"It's gut-wrenching for these families to watch their children deteriorate and to not have a reason," said the program's director of pediatrics, Dr. Cynthia Tifft. "Many of these disorders are not good disorders to have even if you know what they are. But parents will say, 'Even if it's bad news, I just want a name for it.'"
That name, according to Tifft, allows parents to connect with other families facing the same diagnosis.
"Often you can learn as much from those families as you can from a clinician," she said, adding that some disorders are so rare that doctors may only see one case in a lifetime. "It also gives families some idea of what to expect in the future."
Tifft, who is also deputy director of the National Human Genome Research Institute, is using the latest gene sequencing technology to scour Skriver's DNA for clues to her condition.
"We look for genetic changes in the patient that are not seen in the parents or unaffected siblings," she said, explaining how some gene defects cause a cellular build-up of bad proteins and a shortage of good ones. "It's like putting a dam in a river: You get a lake on one side and a trickle on the other."
Discovering the dam opens the door to treatments, according to Tifft.
"Some therapies may be aimed at treating the lake, and others might try to put a hole in the dam to get more water downstream," she said.
But genetic research can take months -- even years. And in the meantime, Skriver needs round-the-clock care, according to her mom.
"It's emotionally exhausting," said Tammy Skriver, who cuts hair out of her home while caring for her daughter. "I just want my daughter back."
Thinking back to the soccer game, Tammy Skriver often wonders if something triggered her daughter's decline, which coincided with a new drug for attention deficit hyperactivity disorder and some school vaccinations.
"I asked [the doctors], 'Could it be that?' But they said it's unrelated," she said.
"We always want a reason for why things happen," said Tifft. "We want to associate it with vaccination or heavy metals in the water -- you name it. Believe me: these moms are racking their brains trying to think of what might have caused this... But I would say 99 percent of time we're able to say, 'There's nothing you did or did not do to cause this.' And that's such a relief." For now, all Tammy Skriver can do is wait for a diagnosis that may never come.
"It would be such a weight lifted off my shoulders," she said. "Even if it's something that's incurable, we'd give it our best fight. We can't even fight it right now because we don't know what it is."
A "Friends of Brianna" Facebook page is collecting donations for Skriver's health care costs -- money her mom hopes will carry her "wild child" through until there's a cure.
"You have so many dreams for your kids," said Tammy Skriver, fantasizing about helping her daughter pick out her prom dress. "I still have the Barbie Jeep and Barbie bike she loved, even though she's way too big for them now. I can't get rid of them because I keep thinking she'll get better and want her stuff."