Brooke Greenberg lived for 20 years, but never developed past the age of two. A rare disorder prevented her from growing more than the size of an infant or acquiring more than a two year old's mental capacity, ABC News reported. She died on Oct. 24.

The second youngest of four sisters, Greenberg was one of approximately twelve known cases of chromosome X, which prevents sufferers from aging, among other medical conditions, ABC News reported.

"The family is doing as well as can be expected," Chris Cole, a colleague of Brooke's father, told ABCNews.com on Tuesday. "They are going through their traditions this week -- the shiva."

Brooke has been through more than a few lifetimes of medical complications -- all of which she survived "without explanation," according to ABC. By the age of six, she'd suffered a stroke, a surgery for stomach ulcers, and 14 days of sleep caused by a brain tumor.

She survived each incident without any noticeable side effects, ABC News reported.

"We were preparing for our child to die," her father Howard Greenberg told ABC in 2009 when the Maryland family appeared on "20/20". "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."

According to Richard F. Walker, a medical researcher at All Children's Hospital in St. Petersburg who has followed Brooke's case since age two, there is no genetic or chromosomal explanation for her condition.

"There've been very minimal changes in Brooke's brain," he said. "Various parts of her body, rather than all being at the same stage, seem to be disconnected."

Her bones were estimated to be around 10 years old, according to ABC News. Believing Brooke's condition could be the key to anti-aging technology, Walker studied her case closely and others like it.

"If we could identify the gene and then at young adulthood we could silence the expression of developmental inertia, find an off-switch, when you do that, there is perfect homeostasis and you are biologically immortal."

All of those afflicted with chromosome X condition have a host of other medical problems, ranging from the inability to walk to the inability to eat, according to ABC News. Brooke couldn't speak and was pushed around a stroller her whole life. She could recognize her sisters and expressed emotions when happy.

According to NBC News, her parents didn't know how serious her condition was at first. Neither did her doctors.

"She really was not growing to the rate that she should have been growing," Mr. Greenberg said. "I remember the doctor saying that when Brooke enters, say, 4th grade she'll be like at the first grade level. We could live with that, we had no problem with that. We really did not know the road we were about to take with Brooke."

"They [the specialists] just said she'll catch up. Then we went to the nutritionist, the endocrinologist. We tried the growth hormone," her mother Melanie Greenberg said.

Rabbi Andrew Busch commented on the impact Brooke's life had on her family.

"While the outside world may have noticed Brooke's physical stature and been puzzled by her unique development state, she brought joy and love to her family," he told the New York Daily News. "Her parents, three sisters and extended family showered her with love and respected her dignity throughout her entire life."

Footage from Brooke's appearance on "20/20" below: