During one cold, spring morning in 2016 Sarah Bowen was dog walking with a friend when she tripped up through the leaves.

Her father was dying with Parkinson’s at the time and her friend turned and asked, “If you could have a test to find out if you would get Parkinson’s too, would you have it?”

Quite startled, Sarah stared at her; she didn’t know how to answer. Would she be brave enough to want to see her future laid out ahead of her? She feared not.

A BBC producer for Radio 4, she realised she wanted to make a programme focusing on someone about to make that kind of decision, “someone braver than me who could look life and death straight in the eye.”

Jackie Harrison of Baliff Bridge, with her brother Mark who has Huntington's disease. Pictured with her dog Sybil.

Her documentary, The Toss of the Coin, chronicles a 15-month journey with a gritty Yorkshirewoman who found the courage to confront her worst fears.

Through the Huntington’s Disease Association Sarah met Jacqui Harrison, “a marvellous, compelling and wry woman” from Brighouse.

Jacqui’s grandfather, uncle and mother all died young with Huntington’s and, since she was 18, she has looked after her brother Mark who is living with Huntington’s too.

Huntington’s is a devastating neuro-degenerative disease that affects muscle co-ordination and movement and causes mental decline and psychological problems. Jacqui explains: “Huntington’s robs you very slowly of everything: the ability to talk, to walk, to move, to think, to swallow.”

It generally affects people in their 30s and 40s. Typically, patients die about 10 to 20 years after symptoms start. About 8,500 people in the UK have Huntington’s and a further 25,000 will develop it when they are older.

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When Sarah asked about the odds of Jacqui also getting Huntington’s she responded simply: “If you have a parent with the gene, a parent who had the disease - so in my case my mother - my odds are completely 50:50, 1 out of 2, complete toss of the coin.”

Sarah made a first visit to Brighouse on September 1, 2016 as Jacqui was mulling over the notion of having a predictive test. It wouldn’t reveal when she will get Huntington’s or how badly, just that she might - or might not.

And although there may be a glimmer of hope for sufferers in the future via new research, there is no presently no cure and no treatment. All that is gained is knowledge.

Given its history of secrecy and shame Jacqui was keen to get people to talk about Huntington’s openly. She said: “In America researchers in the 1920s and even up to recently thought that Huntington’s disease families were tainted by witchcraft. The language around it is fascinating. It is the devil’s disease, a curse. There are so many families hiding it.”

Jackie Harrison of Baliff Bridge, making Hounds for Huntington's.

Given that the test has been available since 1993 Sarah was intrigued as to why Jacqui was considering having it now. Jacqui revealed: “Somebody had said they thought I was very twitchy. You kind of think, ‘Is this the start of it?’”

Reaching her 50th birthday was an incentive for Jacqui to make a decision. She had long ruminated on what to do. As partner Tony said: “Do you want to live the rest of your life in the hope that you may be free of the disease? Or do you want to toss that coin with the negative of that being that you might find out you are not free of it and then you have no hope left?”

In the autumn of 2017 Jacqui found the courage to take the test. Sarah was with her.

“It is an incredibly intense moment when she gets her results,” reveals Sarah.

“Jacqui told me she hoped that if this programme was ever broadcast, in BBC archives there would be a little bit of herself forever, alongside her family who might be elevated from mere asylum statistics.

“Jackie has shown me what true strength and bravery are. We might all need this courage as predicting our own health might soon be the future for all of us.”

The Toss of the Coin is on Radio 4 on Monday, January 22 at 11am as part of The Untold strand, and is presented by Grace Dent. It is downloadable as a podcast: http://www.bbc.co.uk/programmes/b09ntd0k