Like Christine and Anthony Clark, dealing with children’s petty squabbles, tantrums and bad sleeping patterns is a daily battle familiar to most young parents.  But Mr and Mrs Clark are not young parents.  They are in their 60s – an age where most of their friends are enjoying their retirement, and their ‘boys’ are actually fully grown men, each with families of their own.

Brothers Michael,42, and Matthew Clark, 39, from Hull, have been diagnosed with leukodystrophy — a rare genetic disorder that causes a progressive loss of speech and movement.

In the case of Michael and Matthew, it has also made them slowly regress into a childlike state. Where they were once men, they are now young boys, trapped in adult bodies.

The Mail Online first reported the curious case of the Clark brothers earlier this year.

But now their condition is deteriorating to the point where Mrs Clark fears they will no longer be able to walk or feed themselves, like babies.

The family will feature on a Channel Four documentary tonight which follows them on their fascinating and traumatic journey over the last few months as they struggle with their day-to-day life.

Matthew, 39, and his wife had a daughter, Lydia, now 19. She has had a baby, making him a grandfather

Their plight has led to them being likened to the character played by Brad Pitt in the film The Curious Case Of Benjamin Button, an old man who gradually becomes younger.

But Mrs Clark said she finds the analogy upsetting.

Mr and Mrs Clark say when they returned to find their sons had been arguing like toddlers and no longer able to live together.

Michael had moved out of the flat and into a hostel, where workers arranged for him to have medical checks.

When doctors realised he had a brother with similar problems, they ran a series of genetic tests, which revealed both brothers were found to have terminal leukodystrophy.

She told the Independent:  ‘For one thing, they’re not getting smaller – there’s no return to them being cute little boys, they’re big strong men – and that presents a quite different set of problems.’

She said she first realised something ‘was not right’ when she and Mr Clark took them on a family holiday.

The men acted childish throughout, shouting and cheering ‘yippee’ as the plane took off and squabbling like young children. They were both in their thirties at the time.

The men had both been academically bright, with Matthew  offered places both in the Royal Navy and at agricultural college, and Michael joining the RAF at the age of 20.

Both men were married and all had seemed to be going well for them.

Matthew and his wife had a daughter, Lydia – now 19 – and Michael also had stepchildren.

Mr and Mrs Clark decided to take early retirement and then, seven years ago, they sold their home in Gloucestershire and moved to a village near Benidorm, hoping their sons would visit when they could.

But the couple became concerned when Michael and Matthew stopped returning calls.

‘And then, one day, Lydia phoned to say a worker from a hostel had called to say her dad was living there, and there were some problems he needed to discuss,’ Mrs Clark said.

It seems the couple’s departure coincided with their sons’ downward spiral, and the men, by now both divorced, had become gradually unable to look after themselves, and ended up on benefits and sharing a squalid flat.

It means the mens’ brains were being destroyed.

Both intellectually and emotionally, they were returning to their babyhood.

The couple were left with no other option than to leave their dream retirement and return home to care for their sons, who are now getting younger by the day.

Mrs Clark said Michael is the most child-like and moody, and he can’t be left on his own, whereas Matthew talks all the time, saying ‘whatever comes into his head.’

She said: ‘They can be very affectionate, particularly with one another – they’ll often put their arms around one another, and Michael will say, ‘He’s my little brother’. Just like small children, they wake up a lot during the night – I was up seven times with them last night – and, also like children, they’ll deny and deny that they’re tired, even when you can see their eyelids drooping.’

  • The Curious Case of The Clark Brothers, tonight at 9pm on Channel