"My 8-year-old is trapped in a baby's body''

They live half a world apart, but Gabby Williams and Nick Freeman share an incredibly rare and tragic bond - they are "Benjamin Button children".

Only about a half dozen sufferers exist in the world - they age only one year for every four in the life of a normal human being. And medical tests can find nothing wrong with them.

Their families met when Nick - who lives in Western Australia - travelled to the United States to consult with Dr Richard Walker of University of South Florida College of Medicine, who is studying their genetic codes to try and provide answers on how the condition is caused.

Dr Walker says their bodies do not develop as a coordinated unit, but as independent parts that are out of sync. But no known genetic syndromes or chromosomal abnormalities can explain why.

"It was great," said Gabby's mum, Mary, of meeting Nick and his mum Kaylee. "I think Nicky has a lot more abilities than Gabby. He walks and I don't know if she will get to that point. But talking with his mother, there was a connection for me."

Nick and Gabby also starred together in a documentary in the United States called "My 40-year-old Child" in 2011.

Nick is 42 years old but is trapped in a 10-year-old's body. He was born blind and struggled to survive at birth. When he was 1, he said his first words: "Mummy," "Daddy" and "Teddy." But at 14 months old, he stopped talking and hasn't spoken since.

His mother, Kayleen Freeman, told the documentary makers that she was convinced her son understands things, because he will pick up conversations and "burst into laughter." He loves music, "loud and fast" and makes himself understood with his body language. He also has a huge appetite, eating twice what an adult eats.

"He really loves having a massage," Kaylee says. "He comes over to me and shows exactly where he wants his back rubbed."

"He is a fighter and he is meant to be here. He loves horse riding and in the season goes up to three times a week. He loves travel, especially long car trips."

Like Nick, Gabby is blind, but she will never speak.

"She cries when she is hurting and sometimes smiles," says Mary. "But there's not a whole lot of communication."

"She is definitely very slow, but she knows when mama and grandma are holding her," she said. "She comforts to people around her. She knows her sisters, who have watched her quite a bit and listens to them play. We have a wild bunch around here.

Mary admits it's tough not being able to communicate with her daughter, especially when she cries and no-one knows what is wrong.

"That's hard for a mum. Not knowing how to fix it."

But Gabby's ability to connect with people "without even saying a word" is warms her heart.

"It's always the most beautiful thing to see Gabby and how she touches strangers' lives," said Mary. "Whenever we are in public, they stop because of her hair -- how much she has."

Doctors have carried out chromosome tests on Gabby, but can’t find anything unusual other than her frontal lobe not having the characteristic folds.

“It was incredibly frustrating and we were really worried for the first year,"says Mary-Margaret. "The doctors couldn’t give us any advice because they hadn’t seen anything like it before. We just didn’t know what would happen or even if Gabby would survive.”

“We desperately wanted to know what was wrong so we would have idea what the future held, and so we could seek whatever extra help for Gabby she might need,” says Mary. “But it got to the point the doctors said: ‘We just don’t know what the problem is’.”

As time has gone by, Mary-Margaret and husband John have grown used to having an eternal baby. She weighs only 4.5kg, fits in an infant car seat and goes to bed in newborn-sized sleeper suits.

“She still has the same bottle feeds every three hours,” says Mary. But, despite the hardships involved in raising her, “She’s our little angel.”