What is motor neurone disease? Symptoms and causes of Stephen Darby's illness that affected Stephen Hawking

Bolton Wanderers defender Stephen Darby was forced to retire from football today after being diagnosed with motor neurone disease.

Darby, who began his career at his hometown club Liverpool and also played for Bradford, received the diagnosis from a specialist recently.

He has not played since December and retired at 29-years-old.

Other sportsmen who have been diagnosed with the condition include ex-Rangers defender Fernando Ricksen and Scotland international rugby player Doddie Wear, who was diagnosed last year.

South African world cup winner Joost van der Westhuizen sadly died in February last year six years after being diagnosed.

Stephen Hawking was just 21 when he was diagnosed with motor neurone disease which left him paralysed and ultimately unable to speak without the assistance of a computer-driven synthetic voice.

Motor neurone disease is a relatively rare condition only affecting around one in 50,000 people in the UK each year.

The disease kills a third of people within a year and more than half within two years of diagnosis, according to the MND Association.

The condition is fatal and progresses rapidly, and there is no cure, but symptoms can be managed to improve quality of life.

Symptoms develop gradually and while not painful, it is debilitating and affects how you walk, talk, eat, drink and breathe.

It usually occurs on one side of the body first, before getting progressively worse.

Muscles weaken, sufferers can waste way and can be left unable to move or talk properly.

Swallowing and breathing will also become difficult.

People are usually only given a life expectancy of three years on diagnosis, as the function of motor neurons break down, affecting the brain and spinal cord.

Visit the Motor Neurone Disease Association for more information.