In the UK, one family's dark saga of violence, ill health, and medical confidentiality has set the stage for a lawsuit that could irrevocably change the scope of the duty of care doctors owe to the public.

In the latest developments, a woman – who cannot be identified for legal reasons – has won the right to sue her father's doctors, with the trial date having just been set for November next year.

But the sad story of this unlucky family's brush with disease and death goes back more than a decade.

In 2007, the woman's father was convicted of manslaughter with diminished responsibility (due to the state of his mental health), after he fatally shot the woman's mother.

Two years after he was sentenced for the crime, doctors began to suspect that the man might have Huntington's disease – a fatal, progressive brain disorder that causes physical and cognitive impairment, leading to dementia and early death in most people who develop the condition.

Given Huntington's disease has a 50/50 chance of being passed onto offspring, the man's doctors advised him to tell his daughters – the plaintiff in the case, and her two sisters – about their possibly inherited condition.

But the man refused, telling doctors he "was concerned that his daughters should not be informed about the possibility of HD [Huntington's disease] as he felt they might get upset, kill themselves, or have an abortion".

Respecting his right to confidentiality, the doctors kept his condition a secret, even though evidence suggested he was not of right mind to comprehend the gravity of the decision.

In June 2010, a social worker noted, "I do not think that [the father] is able to understand the implications of his illness, the possible speed of his deterioration, or the effects it will have, both on him and his family".

By that point, however, his secret had already had one of its desired effects. Two months earlier, in April 2010, the woman in the case gave birth to a baby daughter.

It was only later that the woman found out by accident about her father's condition, and got herself tested.

In January 2013, the results came back, diagnosing her with Huntington's disease – a diagnosis that meant her young daughter now carried a one-in-two risk of also developing the condition when she grew older.

"I live every day knowing I'm gene positive," the woman told The Times in 2015.

"My young child also has a 50/50 chance of inheriting the disease and will have to live with this legacy… I would never have inflicted this on her. Day by day, she is what makes life worth living and, at the moment that life is great and we're happy. But the future is a terrifying place."

In light of her situation, the woman sued the hospital looking after her father, arguing they owed her a duty of care and negligently failed to advise her of her father's medical condition – even though he had expressly wanted to keep his medical condition a secret from his family.

In 2015, the trial judge struck out the woman's case, on the basis that since the woman was not a patient of the hospital, the doctors did not owe her a duty of care, and that doctors did not have to disclose such information, because doing so would undermine doctor-patient confidentiality.

Last year, on appeal, the Court of Appeal overturned that decision, holding that in certain circumstances – where other parties could be adversely affected by a failure to disclose a patient's medical information – there could potentially be a duty to disclose.

Because of the Court of Appeal's decision, the case will now be heard in a year's time, and this difficult question of law, ethics, and patient rights will now have to be decided.

"This could really change the way we do medicine, because it is about the duty that doctors have to share genetic test results with relatives and whether the duty exists in law," society and ethics researcher Anna Middleton from the Wellcome Genome Campus in Cambridge told The Guardian.

If such a duty is held to exist, it also creates new problems – not just threatening the established principle of patient confidentiality, but imposing a system where people are unilaterally informed they might have serious medical conditions of which they were completely unaware (without themselves seeking medical advice).

"Those relatives might be unhappy to be tracked down and given unwelcome information," Middleton said.

"For example, that they possess a gene that predisposes them to breast cancer. You cannot take back that information once you have given it."