Sixth former Tom Freeman is preparing to run the London Marathon to raise cash to help children like his 11-year-old half-brother, who suffers from a severe form of arthritis.

Tom, 18, from Cope Close, in Botley, Oxford, is hoping to raise £1,500 for the Arthritis Research Campaign, which aims to find a cure for the condition.

His brother Isaac was diagnosed with chronic polyarticular arthritis in 2006.

The affliction left Isaac, a pupil at Cherwell School and a keen footballer, unable to get out of bed unaided.

Isaac, who also suffers from Crohn's disease, has now been put on a special diet and medication for both conditions, which has allowed him to return to school.

But he still cannot play football for his club The Quarry for more than ten minutes without feeling pain the next day.

Tom, who is a pupil at Matthew Arnold School, said: "Isaac was in a lot of pain and missed quite a lot of school because of the arthritis. It was very hard seeing him like that.

"It isn't well known that children can suffer from arthritis, but he was in quite a lot of pain and he got quite low and depressed because he couldn't see an end to it.

"The doctors couldn't work out what it was and that made it even more worrying."

Isaac's, mum Lorraine,corr 45, from Headington, said: "The arthritis got so bad that Isaac couldn't really move at all.

"It was so, so painful. We had to do everything for him, get him out of bed, dress him, help him go to the bathroom.

"It was just so upsetting because he is such an active boy and to go from that to hardly being able to do anything was really difficult.

"We can't believe Tom's going out to do his first marathon for Isaac. It's fantastic, we wish him all the luck in the world and hope he gets round."

Tom, who has been running for 15-months and joined the Kidlington Running Club, said: "The chances are there will be a relapse in Isaac's condition at some point and I want to raise money so they can find a cure and I won't have to see him suffer again.

"This is probably the biggest challenge I've ever taken on but I'll definitely have the thought of Isaac driving me on."

Tom has already raised £569 and has persuaded his school to hold a non-school uniform day later in the year to raise money for ARC.

To donate money to Tom's run visit the website www.justgiving.com/tomfreeman