Little Alexis Skylynd can do most things a typical three year old can do. One of her favorites is playing hide and seek.

One two three four five, counts Lexi as her brother Josh and her mom scramble for hiding spots.

Oh no. You found me! her mom soon calls out in good-natured surprise.

But life for Lexi is also profoundly different. She was born without a chin, her bottom jaw so small and malformed it pushed her tongue into her airway. So ever since birth the little Seattle girl has relied on a tube in her throat for every breath she takes.

We didn't know if she would live once she was born, and what would happen from there, and how her life would be at all, recalls her mother Lisa Skylynd.

Not only can you not breathe which is of course essential. But you also can't eat, explained Skylynd.

For safety, Lexi, who both eats and breathes through tubes, can never be left alone. She works with a speech therapist but also communicates through signing.

Her family saw her jaw deformity as a random birth defect. But Dr. Michael Cunningham, Medical Director of theCraniofacial Center at Seattle Children's, had been on the trail of the condition for years. He'd seen it in another child.

We published the first case, we wrote a paper about the first case, and shortly thereafter were contacted by a family in New Zealand who recognized from the paper that their child had the same condition, said Dr. Cunningham.

His team learned of another child in France, one in Australia, others in the United States, and now Lexi.

We realized that this was actually a pattern that was recognizable and we knew that they all had the same disorder, Dr. Cunningham said.

While the science team was working to zero in on the genes responsible for the condition, they were also helping Lexi. Through a series of surgeries and a painstaking procedure, doctors at Seattle Children's were able to coax Lexi's lower jaw to grow longer, month by month. It has allowed her more room to breathe. Her mother said the next steps will be learning to eat, and to speak more clearly.

Dr. Cunningham and his colleague Mark J. Rieder, PhD of the University of Washington's Department of Genome Sciences used exome sequencing to search for the culprit genes. They finally pinpointed a pair of malfunctioning genes that cause Lexi's rare birth defect, auriculocondylar syndrome. He showed a graphic example of the genes and their effect on a child's jaw.

The top one is a mutation in the a gene called PLCB4, and the bottom one is Lexi. And this is a mutation in GNAI3, he explained. The study findings were published in the American Journal of Human Genetics.

Dr. Cunningham's discovery may hold clues to far more common birth defects, such as Robin sequence, craniofacial microsomia and cleft palate. Lexi's mother has a more personal hope, that knowing of the genes will help her children if they one day want children of their own.

It will be helpful for Lexi and Josh to be able to decide, Skylynd said.

There's more work to be done. The scientists still need to learn what triggers the two genes to go wrong, in hopes of preventing the jaw disorder from happening.

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