She's 8 years old and weighs just 11 pounds.
Gabby Williams feels and looks like a newborn child, and her mother has to care for her like one. Could this curious case of aging hold the key to "biological immortality?"
Gabby is from Billings, Montana, and she is one of just a handful of people in the world with a rare condition that slows the aging process, ABC News reports.
Medical researcher Richard F. Walker has been studying Gabby for two years. His particular interest is investigating the cause of slow aging.
"In some people, something happens to them and the development process is retarded," he said. "The rate of change in the body slows and is negligible."
In an ABC News special to be aired this week, Gabby appears with two others who share her condition: a 29-year-old American with the body of a 10-year-old, and a 31-year-old Brazilian woman who's no bigger than a two-year-old girl.
Walker suspects that Gabby and the others may have a genetic impairment that interferes with a crucial process called "developmental inertia" that affects growth in humans.
"Without that process we never develop," he said.