At 4, she fell into a lethargy that caused her to sleep for 14 days. Then, doctors diagnosed a brain tumor, and the Greenbergs bought a casket for her.
"We were preparing for our child to die," Howard Greenberg said. "We were saying goodbye. And, then, we got a call that there was some change; that Brooke had opened her eyes and she was fine. There was no tumor. She overcomes every obstacle that is thrown her way."
Brooke's doctor said the source of her sudden illnesses remains a mystery.
"We often did not have a good explanation for why she became ill as quickly and intensely as she did," Pakula said. "There were many times in which there were real doubts about her ability to survive."
As she rocks back and forth in a baby swing, Brooke is fed through a tube inserted into her stomach, because her esophagus is so small that swallowed food could back up into her lungs and cause pneumonia.
Doctors recommended growth hormone therapy early in Brooke's life, but the treatment produced no results.
Howard Greenberg recalled the follow-up visit to the endocrinologist. "We took her back in six months, and the doctor looked at us and said, 'Why didn't you give Brooke the growth hormones?' And I said, 'We gave Brooke the growth hormones. We gave her everything you told us to do.' And Brooke didn't put on a pound, an ounce; she didn't grow an inch."
Brooke's hair and her nails are the only two things that grow, Howard said. "She has pajamas and outfits that are 10 or 12 years old," he said.
One of the things she loves most is movement. As Brooke lies on her stomach, Carly often steers her through the house on an ottoman. Brooke also likes to push against open kitchen drawers until they slam shut.
In her crib, "she's very content," Howard said. "She has very little conception of time."
The family has placed a small television near the crib so she can watch whenever she pleases. Her father gets up in the middle of each night to check on her.
Brooke has a caretaker during daytime hours, but the family's schedule revolves around her, year after year. The Greenbergs take no vacations, have few nights out and involve Brooke in as many family activities as possible.
"To go to a swimming pool for the summer, or belong to a summer club ... we tried all those things, and it's lacking something," her mother said. "Brooke's not there. We're not a family without Brooke."
Brooke goes to a Baltimore County public school, Ridge Ruxton, dedicated to special education. Based on her age, she would be a junior in high school. Jewel Adiele, one of Brooke's teachers, said she wonders sometimes what Brooke is thinking or perceiving.
"People who have worked with her in the past or who briefly see her say ... there's no change," Adiele said. "But I think, in her heart, she changes. I think from day to day, there are changes. They're not just as visible as you see in a lot of teens."
To try to determine why Brooke's aging process has been so irregular -- and what it means to the understanding of our genetic makeup -- Walker and Sutcliffe have studied samples of Brooke's cells and DNA to look for what they think may be a genetic mutation never seen before that has affected the way she ages.
Walker, of the University of South Florida, believes that if the gene can be isolated, it may provide clues to questions about why we age and die.