– By the time her mother received the e-mail, Yuna Lee was 2 years old, a child with a frightening medical mystery. Plagued with body-rattling seizures, she could not speak, walk or stand.

“Why is she suffering so much?” her mother, Soo-Kyung Lee, anguished. Brain scans, genetic tests and neurological exams yielded no answers. But when an e-mail popped up suggesting that Yuna might have a mutation on a gene called FOXG1, Lee froze. “I knew,” she said, “what that gene was.”

Almost no one else in the world would have had any idea. But Lee is a specialist in the genetics of the brain — “a star,” said Robert Riddle, a program director in neurogenetics at the National Institute of Neurological Disorders and Stroke.

For years, Lee, a developmental biologist at Oregon Health and Science University, had worked with the FOX family of genes. She also knew harmful FOXG1 mutations are exceedingly rare. Only about 300 people worldwide are known to have the condition.

“It is an astounding story,” Riddle said. “A basic researcher working on something that might help humanity, and it turns out it directly affects her child.”

Suddenly, Lee, 42, and her husband, Jae Lee, 57, another genetics specialist at OHSU, had to transform from dispassionate scientists into parents of a patient, plunged into a fast-moving ocean of newly identified gene mutations, newly named diagnoses and answers that raise new questions. The newfound capacity to sequence genomes is spurring a genetic gold rush, linking mystifying diseases to specific mutations — often random mutations not passed down from parents.

Yuna is now a sweet-natured 8-year-old still wearing a toddler’s onesie over a diaper. “Cognitively she’s about 18 months,” said Jae Lee.

Shortly after Yuna’s second birthday, Soo-Kyung Lee traveled to Washington, D.C., to serve on a National Institutes of Health panel. At dinner, she found herself next to Dr. David Rowitch, a neonatologist and neuroscientist she knew only by reputation.

“She started to tell me what’s going on with her daughter,” recalled Rowitch, who offered to send Yuna’s brain scans to “the world’s expert” in neuroradiology: Dr. Jim Barkovich at UCSF.

Barkovich said Yuna’s scans revealed “a very unusual pattern,” one he had not seen in decades of evaluating brain images. Yuna’s cerebral cortex had abnormal white matter, meaning “there were probably cells dying,” he said, and the corpus callosum, the corridor across which cells in the left and right hemispheres communicate, was “way too thin.”

Searching scientific literature, he said, “I found a gene that seemed to be expressed in that area and found that when it was mutated it caused a very similar pattern.” That gene was FOXG1.

FOXG1 is so crucial that its original name was “Brain Factor 1,” said Dr. William Dobyns, a professor of pediatrics and neurology at University of Washington. “It’s one of the most important genes in brain development.” FOXG1 provides blueprints for a protein that helps other genes switch on or off. It helps with three vital fetal brain stages: delineating the top and bottom regions, adjusting the number of nerve cells produced, and “setting up the organization of the entire cortex,” Dobyns said.

Long before Yuna was born, Soo-Kyung stumbled upon research showing that mice missing both FOXG1 genes did not form brains. That would apply to humans, too. “There’s nobody who is missing two copies of the gene,” Riddle said. “They don’t survive.”

Now, the Lees have identified genes that interact with FOXG1, helping explain why one crippled copy of FOXG1 damages the corpus callosum’s ability to transmit signals between hemispheres. “We now understand how this gene works and why,” Soo-Kyung said.

She rarely used to mention her daughter to fellow scientists, but recently began thanking Yuna during presentations. “I was afraid every day that she might not be with me the next day,” Lee said. “But she’s done amazing things that we wouldn’t dare to dream.”