A look into the pain and the hope of treating rare neurological diseases in children; it's a difficult, sometimes gut-wrenching process with no guarantees, but a Chicago doctor is determined to extend and save lives.

"When I went into child neurology, I actually went into it because there was so little known about it, and I thought there was just a huge black box of opportunity to treat conditions that we didn't even understand what caused them," said Dr. Elizabeth Berry-Kravis, a pediatric neurologist at Rush University Medical Center.

Berry-Kravis ventures deeply into that huge black box every day. Dr. EBK, as her colleagues call her, specializes in rare diseases.

One of her patients, Tessa Jarrin, has TUBB4A leukodystrophy. It's an inherited disorder that affects her ability to eat, speak, and walk.

"It's super rare. There's less than 300 people in the world with this disease. With Tessa's exact variant, there's less than 13 people," said Tessa's mom, Ashley.

"It's very lonely at times, because a lot of people can't relate to what we're going through," said Tessa's dad, Justin.

Ashley and Justin heard about a promising treatment for Tessa's condition, but couldn't find a doctor who would administer it.

Desperate, Ashley attended an event to learn more about the procedure.

"We ultimately put together business cards and pins with Tessa's face on them, just pleading for a doctor to see us, to see my daughter, to help save her," Ashley said. "There we found Dr. Berry-Kravis, and she's like, 'Could you come to Chicago?' I said, 'I will be there tomorrow.'"

The Jarrins brought Tessa to Rush University Medical Center in Chicago all the way from their home in Houston.

"Tessa is here to get an investigational; something called an antisense oligonucleotide, which is going to go in there into her brain, and block the damaging mutation," Berry-Kravis said. "Hopefully that allows us to stop the progression, and maybe even allows Tessa to develop more normally."

Her colleagues said Dr. EBK is big on hope, and big on not sitting still.

"EBK is amazing. She is just a spitfire, fantastic woman," research assistant Rachel Stoub said. "She is nonstop. … She lives off of candy and diet sodas."

A little unorthodox for a diehard marathon runner, who takes the train in from the suburbs, then bikes to Rush and back five days a week. How does she do it all?

"I think I sleep less than most people," she said.

But she wakes up every day optimistic about the future.

"We've discovered more and more and more of the genetic causes of these diseases," Berry-Kravis said. "We're really at a cusp right now where these discoveries are happening very rapidly."

She said, in Tessa's case, doctors can perform gene therapy to replace disease-causing genes with healthy genes, and in the near future could even turn to gene editing.

"We've finally gotten to the point where we can do what I really went into the field to try to discover how to do," she said. "It's just very exciting. … We have the potential to change the courses of these diseases and thereby change the lives of these kids."

Berry-Kravis also is known for uncovering molecular clues in fragile X syndrome, or Martin-Bell syndrome, another genetic disorder that leads to intellectual and developmental disabilities.

To learn more about her work and the challenge of fighting rare diseases, visit rush.edu.

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