Thanks to her parents' hard work, Kate qualified for residency in a home for adults with Prader-Willi in Wisconsin. There she is monitored 24 hours a day and has lost 100 pounds over the past year.
Residents are trained in healthier living and can earn income doing manual labor.
ABC News' John Donvan met up with the Kanes recently when Kate was home for the holidays. The setting was a restaurant, where she demonstrated newfound self-control and ordered just salad.
But there was something odd about Kate's behavior. Her eyes wandered off mid-conversation. It became apparent that she was following the food going to other tables. Kate explained the hunger is always there.
Like Mirabel, Kate would lie to get food. She shoplifted. She sneaked into a neighbor's home for it. She hid food in her closet.
Today, kids born with Prader-Willi can get off to a better start. They can be diagnosed virtually at birth and start hormone therapy to assist in their development.
Driscoll is studying the brains of kids with Prader-Willi. He thinks research into how Prader-Willi Syndrome triggers this condition, what body chemicals are involved and how they interact could yield benefits for everyone who struggles with their weight.
"We think we're going to get major clues by understanding Prader-Willi Syndrome, which is one reason for obesity, that gives us a window of opportunity to go in and help to understand other causes of obesity and, eventually, to figure out what's broken and then how to fix it," Driscoll said.
But Kate and Maribel's ceaseless hunger is a terrible price to pay, even if they can help make a lasting contribution to researchers' understanding of the condition.
Maribel's mom -- who shares her daughter's name -- points out there are also blessings, however. "The blessing is we've learned so much from Maribel," she says.
"A lot of special persons [are] out there," she said. "We should all look and see what they have inside."