By Jane Elliott
Health reporter, BBC News
Mark can no longer smile
When Mark Priddy was diagnosed with Alzheimer's disease at the age of just 36, he and his wife Dione decided to enjoy the time they had left.
They renewed their wedding vows, took a holiday together and tried to make everything as normal as possible for their two young daughters.
But within a year Mark had been admitted to a care home and today, four years later, he cannot walk, talk or smile.
In April, Dione, 40 and from Northampton, is running the London Marathon to raise cash for Alzheimer's research.
Dione knows that nothing can bring back her much-loved husband, but hopes her efforts can help find a cure, or at least help delay the cruel disease, that took Mark from her.
"I've felt helpless watching him gradually fade away but decided I could make a difference by raising money for dementia research," she said.
"Mark and I met at a circuit training class, so running in the Virgin London Marathon seems very appropriate.
"The rigorous training has helped me a great deal, giving me something to focus on and knowing the money I raise will give hope to other people.
"I wish we could have done it together but you just never know what is round the corner."
Rebecca Wood, chief executive of the Alzheimer's Research Trust, said that it was fundraisers like Dione who would help them make the breakthrough so desperately needed.
"Early onset Alzheimer's is rare and it is tragic that Mark has been affected with this dreadful disease," she said.
Mark deteriorated rapidly
"We can't thank Dione enough for all her efforts to raise money for the research we fund, bringing us ever nearer to finding new preventions, treatments and an eventual cure.
"There are 820,000 people in the UK living with the daily reality of Alzheimer's and other forms of dementia, with numbers forecast to double within a generation. More investment into research is desperately needed."
Dr Simon Ridley, research manager at the Alzheimer's Research Trust, agreed: "Early onset dementia can have the most devastating effect on people and their families, often impacting on dependent children and working parents.
"Over 64,000 people in the UK have early onset dementia, and while research into the condition has made inroads in identifying the genetic factors that influence its development, the work remains chronically underfunded.
"If we are to offer hope to people battling with dementia so early in their lives, we have to invest in studies to develop new treatments that can stop the condition in its tracks."
Dione hopes her run will raise between £2-3,000
Meanwhile Dione explained how her loving husband slips further from her.
"Gradually everything has slipped away," she said.
She visits Mark and sits with him. She has decorated his room with photos of their life together and believes that he still knows who she is.
"I go six days a week and chat and read to him and hope he gets something from my visits.
"He responds if I say his name.
"I dreaded the day he didn't smile any more, but you just seem to cope.
"I can't believe we used to go for walks and play pool, things like that."
There are 820,000 people living with dementia in the UK today
163,000 new cases of dementia occur in England and Wales each year - one every 3.2 minutes
One in three of the over 65s will die with some form of dementia
She says the illness has been particularly hard for her two daughters - Eleanor, 13, and Bethany, 11.
Bethany finds it hard to remember Mark as he was and has to rely on videos.
"It was such a hard time with two small children," said Dione.
"I have learnt a lot since Mark was diagnosed but wish I had known more when he was diagnosed and I could have helped support him."
She said that for two years the doctors thought Mark's problems were depression, but she said she thought he knew the truth.
"I think he knew more than we did," she said. "I think he was trying to cover up things such a lot.
"It was probably not until he was diagnosed that we realised how he was suffering.
"I did not really know what Alzheimer's was, to be honest, nor did Mark although he knew there was something wrong.
"We used to go to church every Sunday and I can remember us both breaking down there thinking what is wrong, but we thought if there was an illness the doctors would know."
The Alzheimer's was finally diagnosed after a barrage of tests.
Dione said she just hopes her fundraising will help someone else.
"I can't help Mark, but I can be by his side. The more money that is put into research there will be a cure - there has to be."