Will Martin looks like a healthy 3-year-old, but his bright blue eyes and cheeky smile mask a deadly disease that's powering down his body one cell at a time.
Will has Leigh's disease, a genetic disorder that affects one in 40,000 newborns. And although his case is mild, he's unlikely to live past his seventh birthday.
"That's a pretty hard thing to grasp," said Will's mom, Lori Martin, recalling the devastating diagnosis that came just over a year ago. "We left that appointment pretty shell shocked, went home and just cried."
Leigh's disease disrupts the mitochondria, the cellular power plants that turn food into fuel. As the plants fail, the cells die. And slowly but surely the whole body shuts down.
While scientists see a glimmer of hope in an experimental drug, the current treatment for Leigh's disease is little more than a cocktail of vitamins and supplements.
"There's nothing you can do about it," said Lori Martin, who lives with Will and her husband Neil in Houston. "That's the second gut punch. You want your doctor to have all these magic answers but it doesn't really happen that way."
The disease has already attacked the energy-guzzling cells of Will's developing brain. A recent MRI scan showed four dark swaths of dying nerves in his cerebellum, which controls balance and coordination.
"He can't jump, run, hop or skip, but he gets around," said Lori Martin, adding that leg braces help guard against ankle sprains. "He thinks his fast walking is running. He's really doing quite well for having this diagnosis."
But Will's mitochondria barely keep up with his day-to-day energy demands -- and that's assuming he's healthy.
"One illness puts us in the hospital, and we may never leave," said his self-professed "helicopter mom," always hovering nearby with hand sanitizer in tow. "We try to strike a balance of letting Will be a 3-year-old boy and doing everything we can to keep him from getting sick."
For the doting mother, Will's diagnosis is especially hard to swallow. He inherited the gene defect from her through her mitochondrial DNA. That means she, too may develop symptoms of the disease.
"I'm so focused on Will and his health that that's on the backburner," she said, adding that her mother and two sisters were all found to carry the genetic defect, too. "It also means it's highly likely that any other child we biologically produce together would have Leigh's."
Pediatric neurologist Dr. May Kay Koenig, who treats Will, said Leigh's disease is the hardest diagnosis to deliver.
"People expect their children to be healthy, and to receive a diagnosis like Will's parents did is terrible in the least," said Koenig, director of the Mitochondrial Clinic at the University of Texas, Houston. "But then on top of that to have someone say there's no safe way to reproduce, to have a child of your own, is devastating."
Scientists are searching for a way around that. One possibility is to swap out the mutant mitochondrial DNA with DNA from a donor during in vitro fertilization -- a technique called mitochondrial replacement therapy, which would essentially give one baby three parents.
"It would give parents the family they deserve even though genetics dealt them an ugly hand," said Koenig. "It would be an incredible gift."
But beyond the technical challenges, mitochondrial replacement raises ethical questions about designer babies that could take years to address.
"It's not in my timeline," said Lori Martin, who dreams of giving her son a brother or sister. "But the fact that other women might have that opportunity, I just think that's an incredibly meaningful gift."