Brothers Michael and Matthew Clark fight over Monopoly and throw temper tantrums. They’re also middle-age real-life Benjamin Buttons, suffering from a regenerative disease that has given them the moods and personalities of children.

Michael, 49, and Matthew, 39, once had families but now have to be taken care of by their parents. Michael is a former member of Britain’s Royal Air Force; Matthew held down a job at Walkers Crisps.

But it took only a few years for the brothers and real-life Benjamin Buttons (from the Brad Pitt film and F. Scott Fitzgerald short story “The Curious Case of Benjamin Button") to regress to children after being diagnosed with terminal leukodystrophy, a regenerative disease.

The story of Michael and Matthew Clark aired at 9 p.m. local time Monday on London's Channel 4 and is called “The Curious Case of the Clark Brothers.”

A preview of the documentary, posted on YouTube, shows the brothers being delighted by trains, sticking out their tongues and being amazed by parrots. You can also watch the video above.

“'Benjamin Button’ -- that’s fantasy,” said the brothers’ mother, Christine Clark. “This is real.”

“I used to wish my sons were small again,” the distraught mother added. “I got my wish.”

Only 100 people in Britain are thought to have the rare regenerative disease, with Michael and Matthew the only two brothers known to have the condition.

Christine Clark said she and her husband, Chris Clark, were not told how their sons developed leukodystrophy, which usually occurs in newborns.

“Nobody knows exactly, but it is a genetic condition. Chris and I have been told it is likely we have the same gene deficiency and that there is a 1 in 3 billion chance of two people with the same gene deficiency meeting and becoming parents,” she told the Daily Mail in May. ”And our both having this deficiency has caused this to happen to our sons. There is no cure, and they don’t know how to treat it. We still can’t quite believe it. You just imagine there is some sort of cure out there for every disease.”

Dr. William Kintner, president of the United Leukodystrophy Foundation, said it’s unlikely that the brothers can be cured. He said the best hope for a cure would come before a sufferer starts having the regenerative effects associated with the disease.

"It's very difficult to do anything once progression has occurred," he told Yahoo Shine. "The likelihood that they're on a terminal course are fairly certain, but who knows?"

Chris Clark said his sons’ condition has been a painful experience for the family.

"In the mornings, we have a routine where we have to get a board game out and let [Michael] play with that so that he comes out of his 'state' as we call it,” he told the Telegraph, referring to Michael’s screaming episodes. "It is like an adult having a toddler's tantrum. It's obviously worse for him, but it is terrible for us too. There's nothing we can do to help, and we feel absolutely powerless."