A New Yorker who fascinated doctors because he was resistant to H.I.V. and AIDS has committed suicide, aged 66.
Stephen Crohn was dubbed 'The Man Who Can't Catch AIDS' by The Independent in 1996 after his boyfriend and scores of his friends passed away from the disease but he remained healthy.
Bravely, he volunteered to have his white blood cells exposed to H.I.V. but doctors were unable to infect him - even at concentrations thousands of times stronger than anything that would occur outside a test tube.
But on August 23, he committed suicide, his sister Amy Crohn Santagata said on Friday.
'My brother saw all his friends around him dying, and he didn't die,' Ms Santagata said.
'He went through a tremendous amount of survivor guilt about that and said to himself, "There's got to be a reason."'
She added: 'He was quite extraordinary, and then also quite ordinary.'
Mr Crohn's boyfriend, Jerry Green, a handsome gymnast, was among the first people to die of AIDS in 1982 after contracting the disease in 1978.
Mr Crohn cared for him as he lost 30 pounds, went blind and was eaten away by the mystery illness.
In the years that followed, scores of the couple's friends died of AIDS but he never got ill, despite being as sexually active as them all and not taking any special precautions.
When he realized he was different, he volunteered to work with doctors to find out why.
'I couldn't infect the CD4 cells,' Dr Bill Paxton, who the worked at the Aaron Diamond AIDS Research Center in New York, said. 'I'd never seen that before.'
Years later, researchers isolated the reason. H.I.V. gets into the white blood cells by fitting into two receptors but Mr Crohn's second receptor was flawed due to a genetic defect.
The anomaly, found in less that 1 per cent of the population, saved Mr Crohn's life.
'What he contributed to medical knowledge is really quite extraordinary,' Dr Bruce D. Walker, the director of the Ragon Institute of Massachusetts General Hospital, M.I.T. and Harvard, told The Times.
The research based on Mr Crohn's defective blood cells has led to a drug, maraviroc, that blocks the CCR5 receptor, keeping infection from spreading once patients have caught H.I.V.
According to The Times, an AIDS patient was effectively cured in 2006 after receiving a bone marrow transplant from a donor who had the same mutation.
Mr Crohn was a prolific painter, sculpture and editor and also worked as a social worker in New York. He had recently moved out of Manhattan where he had a studio for many years to Malden-on-Hudson in upstate New York.
In addition to Ms Santagata, Mr Crohn is survived by two other sisters, Carla Crohn Friedman and Judith Bloom, and their children whom he loved.
'My brother was, at times, my best friend,' Ms Santagata wrote on her blog in a memorial to Mr Crohn, adding that he had become depressed in the past decade.
'Although 14 years older than me, he was ever-present, it seemed, and could always make me laugh and we shared a similar sense of wicked humor. We were partners in practical jokes and he was wonderful with my children until the dark clouds overcame him sometime at the turn of the 21st century, a milestone for all us baby boomers.'
Carla Crohn Friedman wrote on Crohn's Facebook page: 'We are all shocked and devastated by this loss and will miss his laughter and big hugs.
'Family was most important to him and he adored being an uncle and great uncle to all of his many nieces and nephews. He was witty, funny, silly and charming. He was very bright and talented in so many areas. He is now at peace and with people who he loved so much on this earth.'
Dr Paxton said he and Mr Crohn remained friends over the years.
'He was the type of guy who walks into the room, and it lights up,' he explained. 'I was going to call him this weekend.'
