James Bexon was just 33 when he was told he had between 20 and 30 years before developing Alzheimer’s.

His father was diagnosed at 58, and in 2018 James took an NHS test which said he had a 99.9% chance of getting a rare, genetic form of the condition.

He qualified for a test because of the strong familial link, which then left him wondering if he might pass it on to his own sons, Elijah and Jacob.

Neither son has inherited the gene which causes genetic Alzheimer’s.

James was living in Tan-lan, Gwynedd, when he started the testing process for genetic young-onset Alzheimer’s.

His father died from the disease in late 2017, shortly before James’ testing began.

Half of his family members have developed the condition over the years.

James had numerous counselling sessions before the blood test in March 2018, to prepare for the chance of bad news.

The results arrived six weeks later.

“The counsellor had a trainee with her, and I read it on her face when I went in,” he said.

“You half expect it anyway, because it’s prominent in the family. Obviously if it was a ‘you haven’t got it’, that would be amazing.

“I just thought that was the hand I’d been dealt, I had that feeling, even though it’s 50/50.”

He added: “The build-up in the protein amyloid, which causes genetic dementia, stops your memory and slows everything down. That starts about 20 or 15 years before you have symptoms.

“So realistically it might have already started – I just don’t know.

“Sometimes you can dwell on it too much. Elijah is five and Jacob is two. As they get older time does go fast.

“Suddenly you’re 40, and actually then I’m not far off being 50.

“There’s people who have their parents around into their 50s or 60s, and I want to have that. I want my kids to have a proper grandad. The kids have Gemma’s stepdad, but on my side they don’t have a grandad.

“It would be nice to live into my 70s, 80s, to be a grumpy old man.”

James and his wife Gemma also had a tough decision to make – whether or not to test their two children for the gene while they were in the womb.

They decided to proceed with the testing, and both children tested negative.

You can only be tested on the NHS in Wales and England for rare inherited forms of dementia, such as frontotemporal dementia and some forms of young-onset Alzheimer’s.

Dementia UK nurse Jules Knight said: “The stats at Dementia UK is 7% to 12% of cases of young-onset are a genetic form of dementia.

“In the UK at the moment, 70,800 people are living with young-onset dementia.”

Drugs such as donanemab, which trials have shown slows cognitive decline, rely on early diagnosis, and private tests for other forms of dementia are not available on the NHS.

Ms Knight said there were some concerns over private tests, which only tell you the risk, rather than NHS tests, which can pinpoint a genetic mutation.

“The NHS test is definitive, in terms of you either have the gene mutation or you don’t,” she said.

“The genetic risk variant, some of us might have the genetic variant some of us might not, but it doesn’t mean you are or aren’t going to develop it.”

She also said the NHS offered extensive emotional support.

“When someone is referred to genetic testing, they should have both pre and post counselling,” Ms Knight said.

“The pre is support around whether you want to go ahead with the testing, the implications around that, and the support you might need.”

For James, who now lives in Evesham, Worcestershire, the NHS test has given his family peace of mind.

“We’re not going to have anymore children, so we know that’s it for genetic Alzheimer’s.

“For me, it was all about trying to stop it in its tracks in our family. There’s only so much you can do, and we’ve done what we can.”