20-year-old Brooke Greenberg has baffled doctors as she remains looking and acting like a toddler despite her age. Greenberg's development is similar to that of a one-year-old toddler - both physically and cognitively.

Greenberg still has her baby teeth and and looks like any other toddler - except that she's 20 years old. Her mysterious condition has been coined 'Syndrome X' by doctors, as they have not seen anything like it and cannot explain or diagnose it.

"From age one to four, Brooke changed," said her father Howard, according to Daily Mail. "She got a little bit bigger. But age four, four to five, she stopped."

Brooke has remained the same size for the last 15 years and still requires 24 hours of care from her parents and travels in a stroller. She has a 17-year-old sister.

"It's been 16 years of on the job training, giving her medicine, knowing when she's sick, knowing the right amount," said her mother Melanie.

Scientists hope to study her unique genetic code to find out more about the process of aging, which could lead to the development of treatments for diseases brought on by old age.

Tests for Brooke show that she may have a gene mutation which stops her from maturing. Dr Eric Schadt, director of the Icahn Institute for Genomics and Multiscale Biology at The Mount Sinai Medical Center in New York, is currently sequencing Brooke's genome. He hopes to find out whether any abnormal genes 'are involved in aging related processes, whether manipulating these genes could increase longevity and/or reduce aging related disorders such as Alzheimer's, heart disease and many forms of cancer,'

Brooke, born in 1993, reportedly suffered and recovered from medical emergencies in the first six years of her life, according to ABC News. She has suffered stomach ulcers and a brain seizer, and recovered fully. She had also fell into a coma at the age of four and slept for 14 days. She was diagnosed with a brain tumor but that tumor had gone by the time she awoke from her coma.