Pope Francis on Thursday threw his weight behind a global push for a cure for deadly Huntingtons disease but said scientists should not use human embryos in stem cell research regarded as the best hope of finding one.
Described as being like Alzheimer's, Parkinson's and schizophrenia rolled into one fatal cocktail, Huntington's (HD) has been associated for centuries with stigmas that have led to social exclusion and hampered efforts to contain the disease.
Campaigners were delighted that Francis agreed to meet with hundreds of families afflicted by a disease so distressing it is often cited as evidence against the existence of a benevolent God.
But scientists and doctors present at the audience disagree fundamentally with the pope's insistence that creating embryos to generate the cells needed for their research should be banned.
He said the use of human embryos to generate cells reflected a "throw-away culture" in science.
"We know that no ends, even noble in themselves, such as a predicted utility for science, for other human beings or for society, can justify the destruction of human embryos."
The stem cell issue is one of several questions that Huntington's, an uncurable neuro-degenerative condition, raises for Catholic teaching.
The Church's objections to artificial contraception and the use of IVF combined with genetic screening are obstacles to measures which could reduce the incidence of a disease most prevalent in strongly Catholic South America.
But Francis's involvement was nonetheless welcomed as a landmark day for hundreds of thousands of sufferers worldwide.
As the pontiff embraced some of those who had travelled to the Vatican, many were overcome by emotion.
Heart of Darkness
"In many cases the sick and their families have experienced the tragedy of shame, isolation and abandonment," Francis told them.
"Hidden no more - it is not simply a slogan, it's a commitment that we all must foster."
Charles Sabine, a former NBC war correspondent who helped organise the event, said Francis's words were hugely significant.
"No pope, in fact no leader of any significance has ever mentioned Huntington's, let alone publicly met with members of families living with the disease," he said.
"That speaks volume about the shame and stigma that surrounds it."
Sabine tested positive for the HD gene 12 years ago and has since dedicated his life to advocacy for sufferers.
"I know I am living on borrowed time," he told AFPTV. "And the worst thing about it is that most of us who suffer it have seen it in our relatives.
"We have watched the future unfold as I did with my father, my half-brother and now my full brother who is in the last stages."
Nearly one in 10 HD sufferers commit suicide before it kills them.
Little understood until the gene that causes it was identified in 1993, the disease induces physical ticks, uncontrolled movements and personality changes before eventually destroying all cerebral function.
It was historically associated with possession and witchcraft, its genetic nature creating notions that afflicted families were cursed.
Such attitudes persist today in South America, where poor sufferers find themselves banished to the margins of society.
In parts of Venezuela, where the gene was identified, as many as one in 10 people are carriers. "I call it the Huntingdon heart of darkness," says Sabine.
Can't afford grave plots
Italian biologist Elena Cattaneo, who is involved in stem cell research on HD, said Thursday's gathering was born of a sense of solidarity with those sufferers.
"The gene was discovered literally thanks to the blood of Venezuelans. Now we in the West have all the advantages of this: genetic testing, recognition of the disease and drugs to treat symptoms -- but they have nothing."
Among the carers Francis met was 79-year-old Colombian, Dilia.
Huntington's took Dilia's husband from her and it is eating its way through the rest of her family so voraciously she cannot afford grave plots for all of them.
The remains of three of the four children she has buried had to be exhumed and reinterred with those of of her husband.
Dilia has seven other children, four now in the final stages of the disease. One grandchild is dead and five more will likely predecease the family matriarch.
"She has basically worked for 50 years as a Huntington's nurse," said Sabine. "I asked her why don't you question your God. She told me 'God is what gets me through each day'."