A 'locked-in' ALS patient has joined the ranks of Oprah, Justin Timberlake and Bill Gates to take the ice bucket challenge for charity.

David McClain, from Texas, has had ALS (amyotrophic lateral sclerosis) for 12 years, and is now completely paralysed.

In the video, posted by his son Ben, he explains via a computer how he tries to keep a positive attitude, thanks to his family, friends and his religion.

He also challenged everyone of his friends on Facebook to follow suit, and donate whatever they can to the ALS Association.

"There is always hope," he says, before a bowl filled with Texas-shaped ice cubes - in honour of his home state - is poured over his head.

David Beckham has become the latest big name to take the challenge, upping the stakes with a barrel-sized portion of icy water.

He nominated Michael Jordan, Leonardo di Caprio and former basketball player Earvin 'Magic' Johnson to take it next.

ALS, also known as Lou Gehrig's Disease after the 20th Century US baseball player whose career was ended by the condition, causes neurons in the brain and spinal cord to die.

This makes it increasingly difficult to move muscles, which eventually stop working altogether.

There is no known cause, aside from a genetic link in a minority of cases, and no known cure.

David has had ALS for 12 years and is completely paralysed Credit: Ben McClain/YouTube

The ALS Foundation has reported rocketing donations since the craze began, with $13.3 million (£8m) being pledged between July 29 and August 17 - compared to just $1.7m (£1m) in the same period last year.

Meanwhile, Mr McClain is also appealing for donations to help his family pay for a new wheelchair van and to cover medical treatment.

Watch: GMB presenters Susanna Reid and Ben Shephard take the Ice Bucket Challenge

Read: Celebrities take on viral ice bucket challenge