WILLIAMSVILLE, NY - A slow but steady walk down the hallway might seem like no small accomplishment for a 3-year-old.
But for Chase Britton, it is nothing short of a medical miracle.
Chase giggles and cheers for himself as he walks, as his parents, Heather and David look on.
How far they've come.
"We've been told an awful lot, by folks who seem to know, or should know, what he should be able to do, and what he's doing, is not that," said David.
With each measured step, Chase is changing what top doctors and researchers around the world thought they knew about the brain.
"There are some very bright specialized people across the country and in Europe that have put their minds to this dilemma," said Dr. Adre du Plessis, Chief of Fetal and Transitional Medicine at Children's National Medical Center in Washington, D.C., "and are continuing to do so, and we haven't come up with an answer. So it is a mystery."
A medical mystery, emerging from within a family that had already seen more than its fair share of heartbreak.
In 2006, the Britton's second child, Trey, died just four weeks after he was born.
Doctors said Trey's condition was not genetic, and the couple was safe to try again.
"We knew this is what we wanted to do," said Heather Britton, "and they said flukes don't happen twice."
Her husband put it even more simply.
"They said lightning doesn't strike twice," said David Britton.
But sometimes, it does.
This time, the pregnancy's complications came early, but when Chase was born, after 35 weeks, doctors said he was healthy.
The only handicap-- he was legally blind. But that was nothing the Britton's couldn't handle.
Throughout Chase's first year, though, Heather says something else seemed "off."
"We knew he was developing a little slower, we thought it was because of the pregnancy," she said.
Worried that he might have mild Cerebral Palsy, Chase's doctor ordered an MRI. The results were expected to take weeks.
The call came the next day.
"He said this is much more complicated than we expected, and very hard to explain," said Heather Britton.
Chase appeared to have a condition that is at once incredibly complicated-- and very simple: he was missing his entire cerebellum.
The cerebellum is the part of the brain responsible for motor control, balance, coordination, emotional control, and now, doctors believe, it plays a role in language and learning.
On top of that, Chase is also missing his pons, the part of the brain stem that regulates basic functions like sleeping and breathing.
"You just assume it means he's going to die," said Heather Britton. "You just assume the worst, because it happened before."
It was bewildering enough that Chase's cerebellum was gone, but because of the complicated pregnancy, the Brittons say they have plenty of proof, in the form of ultrasound pictures, that at some point, it was there.
And that is part of the puzzle that has been eluding Dr. du Plessis.
"That is actually a fundamental part of the dilemma," said du Plessis. "If there was a cerebellum, what happened to it?"
Dr. du Plessis has been meeting with the Brittons for the past two years, on the case that he says is challenging "fundamental principles."
But with so much interest in Chase internationally, Dr. du Plessis believes the impact could reach far beyond the smiling 3-year-old.
"It is cases like this that rally the support of the medical community, that harness the interest of other investigators, that stimulates people to try and find solutions, and those repercussions will have an impact on a much broader population of kids," said Dr. du Plessis.
There is still no official diagnosis, and it's not clear if the condition is genetic or a result of a fetal injury.
"I think the more we learn about these problems, we find out how little we've known all along," said du Plessis, "and how things are not as clear-cut as we thought."
But for Chase's part, he continues to amaze: his doctors, his teachers, just about everyone who meets him.
Chase attends CHC Learning Center in Williamsville several times a week.
"I'm in awe of him everyday," said his teacher, Sharon Schultz. "Things that, based on that diagnosis, he should not be able to do, he is doing, I mean walking up and down the hall, riding a bike, holding a pencil or a pen to work on projects, using scissors."
One of his biggest supporters is big brother Alex.
"He acts like a normal kid," Alex said. "He's not really acting like he doesn't have a cerebellum, he acts normal if you ask me."
And that's why Chase's parents continue to push forward.
"There's constant surprises," Heather Britton said. "You can't stop and say this is it, you have to keep expecting those."
"And he keeps showing us!" said David Britton. "I think it's safe to say I've got great expectations for him."
And with each day seems to come a new accomplishment. Chase has a vocabulary of about sixty words, he's potty training, and he seems to have an intuitive understanding of his new i-pad.
"Anything can happen. He could not sit up forever. He would get up and topple the other way, then he'd get up and topple the other way. Because he did not have that balance center in his brain," said Heather Britton.
David: But he has the drive to keep trying on his own. That's the one thing about him that's extraordinary, is he has drive like I've never seen.
But the drive in this house didn't start with Chase.
"They've always struck me with how dedicated they are, and how committed they are, to this youngster," said Dr. du Plessis.
"You've got to advocate for your kids. If there's something you want for your kids, don't let anyone tell you differently. Find out. Because there's a way," said Heather Britton.
It's not clear yet if Chase will ever be able to live independently.
Dr. du Plessis says its possible, if only because in this case, he's come to expect the unexpected.
"Our geneticist in Buffalo told us to start a college fund, because you never know," said Heather Britton. "So that's our hope for him."