Girl who doesn't age baffles doctors

A 16-year-old girl who is the size of an infant and has the mental capacity of a toddler continues to baffle doctors in the US.

PHOTOS: Medical mystery

Medical experts believe Brooke Greenberg suffers from some kind of genetic mutation that shapes the way she ages, leaving her with the perpetual appearance of a baby.

The exact cause of the phenomenon has not been pinpointed.

Doctors say Brooke is not growing in a coordinated way, with her body parts out of synchronisation, as if each has a mind of its own.

"Why doesn't she age?" her father, Howard Greenberg, asked on US network ABC.

"Is she the fountain of youth?"

Brooke's mother Melanie Greenberg, 48, said she was so used to people asking how old her daughter is she did not even try to explain.

"My system always has been to turn years into months," Mrs Greenberg said.

"So if someone asked today, I might say she's 16 months old."

Brooke, who is 76cm tall and weighs 7kg, does not speak but has a distinctive laugh and clearly recognises people she knows.

She has three sisters aged between 13 and 22, all of who have developed normally and are used to their family getting unusual attention.

"She looks like a six-month-old, but she kind of has the personality of a 16-year-old," said sister Caitlin, 19.

Brooke has been plagued by medical problems since she was born, at one point diagnosed with a brain tumour that doctors thought would be terminal.

Her parents bought a casket in preparation, but new tests remarkably revealed there was no tumour.

Doctors say although there are other cases of people with abnormal development, Brooke seems to be unique.

"Many of the best-known names in medicine, in their experience ... had not seen anyone who matched up to Brooke," said pediatrician Lawrence Pakula from the Johns Hopkins School of Medicine.

"She is always a surprise."

But doctors hope that Brooke may even be able to provide important clues as to how human beings age.

If the specific DNA behind the phenomenon can be isolated, they may even be able to learn how to slow the ageing process.

"Without being sensational, I'd say this is an opportunity for us to answer the question [of] why we're mortal, or at least to test it," said Dr Richard Walker from the University of South Florida College of Medicine.

"And if we're wrong, we can discard it. But if we're right, we've got the golden ring."