Without treatment, Forloni predicts that at least four of the 10 subjects carrying the mutation would be expected to succumb within the next decade. So if the team find that more than six have escaped the disease by the end of that period, they will consider the trial a success – perhaps justifying more widespread use.

Despite the glimmer of hope it offers, the trial remains controversial among some of the doctors who have been following this family closely. Cortelli, for one, has decided not to be involved in the project because he is concerned about its ethics. Some of the side effects of the antibiotics may still give away the subjects’ diagnosis, causing unnecessary distress, he thinks. (In their defence, Roiter and Forloni’s team will be providing psychological support throughout the experiment.) In any case, he is sceptical that the evidence for the drug’s potential is not strong enough to justify such an extended period of treatment.

And even if the family members have escaped the disease at the end of the trial, Cortelli says we can’t rule out the possibility that these few individuals were simply lucky; some people with the mutation have still lived into their 80s, although no one knows why their gene remained dormant.

But with anxiety and uncertainty plaguing them whatever they decide, it’s not hard to see why the family is willing to take a gamble on the treatment: here is a chance to absolve the death sentence that has been written in their DNA for centuries.

Silvano’s niece once spoke of creeping into her mother’s room each night to check that she was really asleep and not hiding the first signs of insomnia. She was, she said, a “spy in her own home”. If the drug really does work, it would be the end of this living nightmare – the start of a future in which the solace of a night’s sleep can be embraced without fearing it could soon be the last.

David Robson is BBC Future’s feature writer. He is @d_a_robson on twitter.

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