U2 drummer's rare diagnosis leaves him 'pained' during performances

"I've always known that there's something not particularly right with the way that I deal with numbers," he explained. "I'm numerically challenged. And I realized recently that I have dyscalculia, which is a sub-version of dyslexia. So I can't count [and] I can't add."

He shared, "When people watch me play sometimes, they say, 'you look pained.' I am pained because I'm trying to count the bars. I had to find ways of doing this - and counting bars is like climbing Everest."

While symptoms typically begin appearing in childhood, it often goes undiagnosed.

The Cleveland Clinic also notes that people who have dyscalculia "often face mental health issues when they have to do math, such as anxiety, depression and other difficult feelings."

Dyscalculia is similar to the more commonly known dyslexia in that they both fall under the diagnosis of "specific learning disorder" as outlined in the American Psychiatric Association's Diagnostic and Statistic Manual of Mental Disorders (the DSM-5), but while dyscalculia deals with a person's ability to do math, dyslexia deals with a person's ability to read.

The drummer wrote and produced the music for the movie, which debuted in October at the Woodstock Film Festival. In speaking about the film, he has revealed that his son has dyslexia.

He held auditions in the kitchen of his home, and Adam Clayton, David Evans (known as The Edge) and Paul Hewson (Bono) all turned up. While the band has had some disagreements over the years, they've been together ever since.