The teenager suffers an extremely rare condition that means if he falls asleep without the proper medical equipment he will stop breathing.

He was born with Ondine's Curse, known by its official name congenital central hypoventilation syndrome.

It causes a person to stop breathing, because the patient's lungs can't function properly when they are sleeping.

So severe is Liam's condition, he has to be hooked up to a life-support machine and watched by a carer throughout the night, to keep him alive.

Doctors gave Liam just six weeks to live when he was born.

But, he's defied the odds and later this year will celebrate his 18th birthday.

The teenager's parents Peter and Kim, from Gosport, South Hampshire, play a key role in his care team, monitoring their son 24 hours a day, with specialist GPS equipment.

Kim, 56, said: “Central hypoventilation syndrome basically implies that when you sleep, your phrenic nerve doesn’t kick in so your brain doesn’t tell you to breathe.

“We rely on a machine to make him breathe and without that, he wouldn’t be alive.

"If he doesn’t breathe, he dies - that’s it.

“His condition is extremely rare and if we would have listened to some doctors he shouldn’t be alive right now.

“He had the intent for life and so that became our job to make sure he was offered that.”

Liam's condition means that despite being a teenager he has a very strict bedtime routine.

Dad Peter usually takes charge of plugging his son into the ventilator machine and making sure everything is in order for the carer to sit and watch him sleep.

He said: “If you ask me if I had a good night sleep the answer is no, not since the day he was born to be quite frank.

“You're constantly on alert and worry that perhaps it’s the last time you are saying good night.

“On the left hand side (of Liam's bed) we have all of his ventilator equipment.

"The idea is that a ventilator supplies positive pressure so that Liam is actually forced to exhale CO2, which normally you or I would naturally.

“There is also a plate under the mattress that will sense any sort of fitting and then the only way of making sure that he is still breathing is via that type of mask.

“Besides a medical room, it’s also his room and so you have got his PlayStation, the set TV and then Liam’s big forte – his Lego, which is all around the room.”

It's so rare, only around 1,500 cases have been reported across the world.

The condition is life-threatening and affects the central nervous system.

The most common symptom is being unable to breathe properly while you're asleep.

It means sufferers have to be hooked up to a ventilator to help them breathe.

The cause of CCHS is thought to be genetic, caused by a mutation to a specific gene.

As well as the sleeping condition, Liam also lost a large part of his bowel when he was born.

In its place he has an ileostomy bag.

His mum, Kim said: "Food is a big issue for Liam.

"I have to plan every day and every way – the amount of food he goes through is quite terrifying.

"And it’s imperative that he has drugs with whatever he is eating or he can begin to lose weight extremely quickly.”

Despite not having the same learning abilities as other 17-year-olds, Liam attends a normal school, and loves to draw and create Lego models.

Liam's parents have no idea how long he might live, given his condition is so rare - affecting just 1,500 people across the world.

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Peter said: "We've gone from nothing towards 18.

"I'm extremely proud of him. I would have given up a long time ago.

"I couldn't have lived with the condition he has and put up with what he has, with the pain levels."

Mum Kim, added: “Liam is 17, nearly 18, so it’s a big birthday this year!

“He is an annoying, grumpy teenager so he is no different to any other teenager but he does have a sense of humour and he is very caring – he’s got a really soft side.

“You can’t regret anything you have done – we’ve had 18 years of his life so day to day you can’t regret anything.”