Chase Britton represents the kind of medical case that doctors look at with intense curiosity.
He lacks a cerebellum, an important part of the brain responsible for such basics as controlling the body's movement and balance.
A cerebellum was once visible at the base of his brain -- doctors saw it on an ultrasound image before he was born -- and some remnant should remain; otherwise, the 3-year-old from Clarence probably would not be alive.
But images show a fluid-filled space where the cerebellum once was.
"We joke that cerebellums are overrated," said David Britton, his father.
Chase's medical problem is not unique but is very rare, and for a short time, news of it caused a stir on the Internet, with doctors and others debating on medical forums and blogs whether his case represented a deep medical mystery or even evidence of an independent soul.
"We found out there are a lot of armchair surgeons out there," said Heather, his mother.
Chase's story, as well as the progress he has made despite not having a critical part of his brain, is not miraculous. But his condition is not yet completely understood.
Some infants are born with underdeveloped cerebellums or with cerebellums that waste away for a variety of reasons. The technical name for the phenomenon is cerebellar hypoplasia.
In some instances, the cause is a genetic defect. In others, injuries from infections, strokes or other medical problems cause the cerebellum to atrophy.
Chase is among a small group of children in which the exact cause remains unclear, although a genetic link is suspected. Only about six such children have been identified in the country, said Dr. Luther Robinson, director of dysmorphology and clinical genetics at Women & Children's Hospital.
"We have not found an unequivocal cause," Robinson said. "There is no evidence of injury or infection, and we have checked for many of the known and not-so-common gene mutations that can influence cerebellar development."
A genetic defect is suspected because Chase also suffers from colobomas -- gaps in the structure of the eyes. The thinking is that, with such disparate abnormalities and no sign of an illness or injury, there may be a single genetic connection. It just hasn't been identified yet.
That's not unusual. Some birth defects are difficult to recognize and their cause not obviously apparent.
"It's a remarkably unusual association of brain developments and may be unique," said Robinson, who has coordinated Chase's care in Buffalo and with experts elsewhere, including Seattle and Washington, D.C.
Chase, for instance, is part of an effort by Dr. William Dobyns, a researcher at the Seattle Children's Hospital Research Foundation, to study the handful of known children with a similar set of conditions.
The Brittons, who have another son, Alex, 13, now are home as a family quietly moving forward with the daily struggles of raising a child with disabilities and doing it with an upbeat attitude about his future.
Chase is behind others his age cognitively, and he can move but with poor coordination. His vision is impaired, but he can recognize colors and letters. To the Brittons, what's important is that their son is progressing, albeit slowly, and not regressing.
"We call it Chase pace," his father said.
To be born without a cerebellum is often fatal or the cause of serious disabilities. In some cases, however, the brain displays its ability to rewire somewhat during childhood, with other parts compensating for the loss.
Chase, for instance, is able to drive his electric wheelchair. He has a 100-word vocabulary. He is curious and seems to push himself to do more.
The family's hope is that he can one day live an independent life.
"Chase is doing a lot better than people expected. He has a severe defect but somehow is going about his merry way. We're cautiously optimistic about him," Robinson said.
His mother suffered an unusually difficult pregnancy in which her water broke 18 weeks into the pregnancy, and Chase was delivered by Caesarean section five weeks prematurely in Women & Children's.
Other than his small size, he appeared relatively healthy while he spent his first four weeks in the neonatal intensive care unit.
But signs of trouble began to appear. He didn't crawl and couldn't sit up, and a doctor did an exam and found the structural eye defects.
An MRI was scheduled, and the medical staff initially began to discuss the possibility that Chase suffered from cerebral palsy, a group of chronic movement or posture disorders.
"The next day we got the MRI results -- there was a pocket of fluid where his cerebellum should be," his mother said. "There was no sign of trauma, such as from a stroke, so it was bizarre because we have an ultrasound of Chase at the 26th week of the pregnancy that shows the cerebellum was there."
She wants to know what happened. Chase's father is ready to move on whether or not they ever get an explanation.
During the pregnancy and shortly after the birth, more than one medical professional had warned the Brittons that Chase's image from the MRI was that of a "vegetable." They worried about the challenge that lay ahead of them if their son turned out to be profoundly disabled.
So, it was incredibly gratifying recently when a doctor told them to think about starting a college fund.
"There is an inspirational side to Chase's story," his mother said. "It's about how this kid challenges himself, and it's also about staring adversity in the face and dealing with it."