Brooke Greenberg, who was diagnosed with “Syndrome X” after doctors discovered she could not grow physically or mentally, has passed away at the age of 20. The resident of Reisterstown, Md., was said to be one of 10 people in the world suffering from this rare and inexplicable disease.

“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,” Rabi Andrew Busch, who read Brooke's eulogy at her funeral this past Sunday, told the NY Daily News.

Even though she was born a month premature at Sinai Hospital in Baltimore, Md., doctors were not aware that something was wrong at first. At 4 lbs., Brooke did require surgery to correct another rare condition known as anterior hip dislocation, but she seemed healthy otherwise.

Brooke’s parents, Howard and Melanie, took her to pediatricians, geneticists, and other specialists in hopes of pinpointing her condition. Even the staff at Johns Hopkins Medical Center and New York’s Mount Sinai Hospital were unable to give the Greenberg family an answer. Brooke’s DNA was even tested to help scientists understand how humans age and possibly devise a method for prolonging youth.

"She literally is the fountain of youth if you think about it," Howard Greenberg told NBC. "She's shown me that as hard as it gets sometimes, the next day it can only get better."

Abnormalities in her chromosomes and genetics failed to explain why her hair and fingernails were the only parts of her body that grew. Between the age of 4 and 5, she stopped growing completely. Finally, it was Brooke’s own physician who diagnosed her with Syndrome X.

"We started hearing the word maybe she has 'Syndrome X' which is an unknown syndrome," Melanie told NBC. "That was the first time after the growth hormone didn’t work that the doctor brought that up into our minds and it seemed like the thing to label Brooke, unknown 'Syndrome X.'"

Brooke is survived by her parents and her three sisters, Emily, Caitlin, and Carly. “Her parents, three sisters and extended family showered her with love and respected her dignity throughout her entire life,” Rabi Busch added.