Video: 'My life expectancy will be shorter by far than my friends and my wife': John Mann on Alzheimer's diagnosis

In the late summer air, the sweaty, bopping parents-and-kids crowd twirled and pogoed to this nation’s definitive party song, joining in as John Mann belted out perhaps the most sung-along-to lyric in Canadian music: “You’ll have to excuse me, I’m not at my best.” During this recent concert at Vancouver’s Pacific National Exhibition, the line – from the seminal Spirit of the West tune Home for a Rest – was bursting with double-meaning. Soon Mr. Mann would reveal a closely guarded terrible truth.

There were clues: his empty hands – no guitar; the onstage banter left for the most part to fellow frontman Geoffrey Kelly; the iPad affixed to Mr. Mann’s microphone stand. He can no longer trust himself to keep his guitar-playing at pace with the band, to tell those great stories from the stage, to even remember the lyrical poetry he himself wrote – words he has sung countless times criss-crossing Canada and the world.

At 51, Mr. Mann has early onset Alzheimer’s disease.

“I just want people to know now, because we’ve been holding this in as a band, waiting for the right time, and I was getting a bit antsy,” Mr. Mann says during a lengthy interview at his Vancouver home, conducted with his wife Jill Daum, who fills in many of the blanks. “I’m John’s brain,” she says.

The devastating diagnosis came about a year ago. Long before that, there was evidence so compelling that Mr. Mann, still in his 40s, went to his family doctor with concerns he had dementia. But his intensifying problems were thought to have been caused by the colorectal cancer from which he had also been suffering, and the stress of it all. He is now in remission.

But as the brain fog intensified, it became more and more clear that something was very wrong.

“He started having trouble with the chords or the lyrics to songs we’ve been playing for a really long time, songs like Home for a Rest, songs that we played every single night,” Mr. Kelly says. “At first you’d kind of be mad at him, like how can he keep screwing that up, none of us aware that he had what he has.”

Vince Ditrich, Spirit’s drummer and manager, felt certain there was a serious problem. “So I called John and I said ‘Johnny, something’s not right. Are you okay? What can we do?’ And he was magnificent about it. He was so brave. He didn’t get defensive. He didn’t get a chip on his shoulder. He didn’t say: ‘You make mistakes too,’” Mr. Ditrich recalls. “That was the very first step towards the group’s consciousness that there was something clinically wrong with him.”

Ms. Daum was noticing the decline, too. Mr. Mann, who was also a busy film, TV and stage actor, was struggling with his lines. Remembering entrances for Blood Brothers, at Vancouver’s Arts Club Theatre in late 2011, was a nightmare. “He had the therapist talking to him outside the rehearsal door, just trying to calm him down, because he was having so much trouble,” says Ms. Daum, who is also an actor and playwright best known for Mom’s the Word.

It got to the point where Mr. Mann could barely get through an audition. Frustrated initially when trying to run lines with her husband, Ms. Daum grew gravely concerned.

With the help of a friend, who is a geriatrician, a diagnosis was finally made. This was a shattering experience. Ms. Daum – who is a strong woman, full of positive energy and laughter – breaks down as she describes what happened. She was called in to the doctor’s office, told her husband had Alzheimer’s and asked when it would be best to tell him. She lived with that news for days before he was told, suffering in excruciating silence as she drove him to the appointment where she knew he was about to receive the crushing news.

Telling the kids – Harlan, 23 and Hattie, 21 – “was the hardest thing,” Ms. Daum says quietly.

And then they embraced a common coping mechanism – denial.

“It took us six months to sit down and have the conversation to go, this actually is not going to go away, and this is not going to get better,” Ms. Daum says. “So we have to just go, we really have to acknowledge how shitty this is and how sad it is and carry on in that mode and try to suck the most out of it we can.”