Brooke Greenberg is 20 years old but you won't guess from her appearance. For 15 years, she has remained in the physical and mental developmental stage of a toddler with an estimated mental age of about nine months to one year.
The Daily Mail reports that Greenberg, who appeared on Katie Couric's show with her mother Melanie, her father Howard and 17-year-old sister Carly, is unable to walk. She still has baby teeth and she is carried around like an infant.
Doctors are baffled and struggling to explain what happened to her and caused the permanent suspension of her development.
Her parents revealed to Couric that they noticed soon after she reached age four, that she had stopped growing altogether. Not only did she stop growing physically, she also stopped growing mentally.
Her father Howard Greenberg, explained: "From age one to four, Brooke changed. She got a little bit bigger. But age four, four to five, she stopped."
The Daily Mail reports she has stayed the same size for 15 years.
According to Shine Yahoo!, Brooke Greenberg is literally a 20-year-old toddler. She is 20 inches tall and weighs just 16 pounds. Her story came to public attention when she recently appeared on Kate Couric's show.
Melanie, describing her daughter's personality, said: "Like 6 months, If she's happy, she'll giggle and laugh."
Brooke Greenberg is the world's only case of 'Syndrome X'
Greenberg remains a medical mystery. Like an infant, she wears diapers and needs 24-hour care and attention. She is fed through a tube inserted into her stomach, because her esophagus is so small that swallowed food could run back into her lungs and cause pneumonia, the Daily Mail reports.
Her mother, Melanie Greenberg, said: "It's been 16 years of on the job training, giving her medicine, knowing when she's sick, knowing the right amount."
Her father Howard Greenberg, said: "The key with Brooke is we don't know what tomorrow brings."
According to the Daily Mail, Mrs Greenberg said that when a mother with a toddler asks her how old Brooke is, she would usually not tell the truth. She said: "My system always has been to turn years into months. So, if someone asked today, I might say, she's  months old."
Doctors say hers is the only case of its kind. Because they have no other case for reference, doctors cannot even make a guess at the outcome of her condition, or how long they can expect she would live.
The Examiner reports that according to an expert who has been studying the 20-year-old toddler, "It hasn't been easy. We don’t have anybody really to turn to, to tell us what to expect."
Greenberg has been examined by some of the best doctors from the best medical institutions in the US. But no one has been able to dream up a formal diagnosis of her condition. But in the effort to give a name to their ignorance, doctors have called her condition "Syndrome X."
Dr Eric Schadt, director of the Icahn Institute for Genomics and Multiscale Biology at The Mount Sinai Medical Center in New York, says there are "no apparent abnormalities in her endocrine system, no gross chromosomal abnormalities, or any of the other disruptions known to occur in humans that can cause developmental issues."
The Daily Mail reports scientists believe that a genetic mutation may be responsible for the permanent arrest of her physical and mental development. They believe that a study of her genetic code could provide fresh insights into aging and lead ultimately to development of new therapies for treating age-related diseases.
Scientists are in the process of sequencing Greenberg's entire genome. They will be paying attention to genomic sequences involved in aging-related processes. The potential finds are exciting to contemplate. Scientists may discover genes that switch on and off critical processes related to aging and help advance research into longevity and diseases of old age, such as Alzheimer's, Parkinson's disease, cancer and cardiovascular disorders.
Her father said on Kate Couric's show: "The reason we are doing it isn't to put my family on television. Finding out that her DNA makeup [could be] completely different than anyone else's brought to our attention that we could help. So eventually, at the end of the rainbow, there will be something that comes out of all this. I believe everyone is here for a reason."
According to ABC News, in the first six years of her life, Brooke suffered a number of medical emergencies that she recovered from miraculously. She survived surgery for seven perforated stomach ulcers. She also survived a brain seizure and a stroke that healed completely within weeks.
When she was four years old, she fell into a coma for 14 days. Doctors diagnosed a brain tumor, but by the time she came out of the coma, the tumor and disappeared mysteriously.
Is it possible that Greenberg's novel genetic makeup enhances her body's self-regenerating and healing capacities? Genetic and medical studies of the mysterious condition "Syndrome X" may reveal astounding new facts to scientists.