By Jane Elliott
BBC News , health reporter
When Linda Beer's sister needed a kidney she did not hesitate to offer one of her own.
Linda knew her sister faced death without transplant
Even though doctors warned her that her sister's body could eventually also destroy the new healthy kidney.
For years, Carol Whitby had been suffering from severe systematic lupus - an autoimmune illness that occurs when the immune system becomes unable to distinguish its own tissues and starts attacking itself.
As the condition worsened Carol needed regular dialysis and her body weakened.
Linda, aged 40, from Paignton, Devon, said her immediate response had been to offer Carol her own organ.
"Carol had been so poorly. And then last year when we were away on holiday she had to be rushed into hospital as the lupus had really attacked her.
"There was nothing they could do and they thought she could have died.
"They were going over what they could do and said they would put Carol on the transplant list, but that she might not last the 18 months she might have to wait for a transplant.
"I just wanted them to test whether I could give her my kidney. I would have cut off my right arm if she had needed it."
Linda was warned her tissue might not be compatible, but when the tests came back the match was almost identical.
"A lot of my family were worried because I have three children, but on the other hand they recognised that it was my life and that if I had not done this Carol could have died."
Linda said she had no regrets, even though her husband had to give up his job to care for her and the children after the operation.
Carol, aged 43, said she and her sister had always been close, but she was still overwhelmed by Linda's gesture.
Around one in 250 Afro-Caribbeans have lupus, compared to one in 1,000 Caucasians
Lupus patients between the ages of 35-40 are 50 times more likely to have a heart attack
She said Linda had been extremely brave, although she admitted that at first she had been reluctant for Linda to risk her own health.
"I knew I was going on the transplant list, but when she suggested giving me her kidney I said 'no', because she had responsibilities.
"I knew I might not survive the operation, but I always knew the actual operation was harder on the donor.
"Linda was very brave. She is one in a million."
Professor David Isenberg, of University College, London, said the condition was often difficult to diagnose because of its 'chameleon' like qualities.
He said patients could suffer a variety of symptoms including joint pains, skin rashes, tiredness and exhaustion as well as swollen glands, fever and hair loss.
In severe forms the disease can also attack the kidneys, heart, lungs and brain and can prove fatal.
"We expect to be healthy so when people are diagnosed with this in their 20s they get a shock," said Professor Isenberg.
"This is a condition that carries a significant risk of morbidity."
He said that despite the fact that there is currently no cure, things are looking brighter.
"In the 50s there was a 50% five-year survival rate and now it is an 85% 15-year survival rate.
"And the progress on drugs to help is much improved. There are still a lot of health problems, but the future is very much brighter for lupus patients."