When Liam Derbyshire was born, doctors said he would not live for more than six weeks. In a few months he will turn 18.

It is estimated that in the world only 1,500 people have the same rare disease as the teenager .

Liam was born with Ondine's Curse, officially known as Congenital Central Hypoventilation Syndrome, which causes respiratory arrest due to a patient's lungs not functioning when they are asleep .

The condition means the 17-year-old has to be plugged into a life support machine and watched by a carer every night to keep him alive.

Doctors gave Liam just six weeks to live after birth, but later this year the young man from Gosport, South Hampshire, is turning 18 and has truly defied all odds.

Liam's parents, Peter and Kim, act as a major part of his caring team and monitor their son 24 hours a day with specialised 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 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 are constantly on the alert and you worry that perhaps it's the last time you are saying good night.

"Liam's sleeping arrangements are the electric bed which has three positions - it can be up or down and the head and feet can be lifted independently in order to give him some quality sleep.

"On the left hand side 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."

Liam also struggles with a bowel condition, something unrelated to Central Hyperventilation, which means he must eat substantially large portions of food throughout the day to keep his body functioning.

Kim said: "He lost a substantial part of his bowel when he was first born and now has an ileostomy bag, which he has had for many, many years.

Read more on mirror.co.uk.