A 20-year-old woman who was born premature at just under four pounds has died. Brooke Greenberg from Reistertown in the U.S. had an extremely rare condition known only as Syndrome X which left doctors and the medical world scratching their heads for despite her age, she still acted and looked like a toddler.

At Ms Greenberg's funeral, Rabi Andrew Bush who delivered the eulogy, said she had brought joy and love to her family. Her parents and three sisters showed Ms Greenberg love and respected her dignity as a human being.

According to her parents, Brooke Greenberg had stopped normal development at the age of 5. Howard Greenberg said his child came out on the small side, but she was "nothing abnormal." The parents recalled how Brooke had arrived a month earlier than expected and had a rare anterior hip dislocation. She needed surgery to correct her dislocated hips which caused her legs to be in an awkward position, according to pediatrician Lawrence Pakula.

The Greenbergs realised that something was wrong with Brooke when her younger sister has outgrown her. They sought medical help, but doctors did not know her condition. They only told her parents to prepare for her death because of the mysterious condition.

Reports said that doctors will study her DNA to learn more of how people age and unlock the fountain of youth.

Other cases

In some cases, others believed to be hold the key to biological immortality are lucky to be alive.

At 8 years old, Gabby needs to be cared for like a baby. Her parents change her diapers and feed her frequently. Her mother, Mary Margaret Williams, said Gabby's skin and hair hasn't changed much in all of 8 years. Gabby still has baby-smooth skin and fine hair.

Gabby grew taller, according to Ms. Williams in an interview with ABC News. The tiny eight-year-old wears size 3-6 months clothes since she became a little taller.

Gabby is one of the few people in the world with the condition that kept them from aging like the average human being. Scientists have yet to name this type of condition since it is rare.

Scientists have previously found 2 more people with similar symptoms. The TLC network featured Gabby's story, along with Nicky Freeman, a 40-year-old Australian man who looks like a 10-year-old. The documentary special was shown on TLC in 2011.