A 12-year-old boy who has one of the rarest diseases in the world -- only 200 others have vanishing bones syndrome -- has started to re-grow tissue.

New bone has been discovered in the spine of Joshua Leighton, reversing the disease which struck him three years ago.

Now Joshua and his mum and dad, Sharon, 45, and Richard, 46, of Coles Way, Riddlesden, are optimistic for the future.

And they hope one day he will be able to throw away the body plaster cast he wears 24 hours a day.

The good news comes as Joshua has been awarded student of the year in his year group at Greenhead School, Utley, where his 16 year-old brother Jonathan is also a pupil.

Only about 200 people in the world have the disease, in which abnormal tissue produces chemicals that disintegrate bone.

And Joshua is one of only 20 people worldwide with the disease in the spine.

But his medical team at St James's Hospital, Leeds, led by consultant spinal and orthopaedic surgeon Peter Millner, have seen the disease reversing.

Joshua has had to put up with sickness and discomfort from the drugs he takes every day.

And the substance he needs to swallow to undergo a scan makes him sick.

But Mr Millner said he was a model patient and cautiously optimistic about his improvement.

"We hope in time -- we don't know when -- he will be strong enough to do without his plaster cast jacket.

"It looks like he is growing bone -- we have to do another scan to show the bone density but last time it showed improvement."

He praised Joshua and his family for the understanding and co-operation in the experimental treatment.

Joshua takes a cocktail of interferon and calcitonin administered by his mum by injection.

Mr Millner said the success was also down to the wider medical team involved.

Joshua said: "I have been taking drugs to make my spine stronger. I'm coping with it OK.

"My back doesn't ache as much as it used to. The treatment hurts at times and it makes me feel sick but it is making me better.

"I'm hoping that in a few years time I won't need the plaster cast."

His mum, a non-teaching assistant, said the news was "brilliant".

"We are much more optimistic. And we know Mr Millner will do his best," she said.

"We are very proud of Joshua. He is also doing well at school. Nothing phases him."

Judith Smith, Greenhead's assistant head teacher and special needs co-ordinator, said: "Joshua has a stalwart approach -- he gets on with it despite everything. He is a great boy to have in school."