Larry Mullen Jr. of U2 fame has a diagnosis that makes playing music difficult.

Mullen, drummer and founding member of the Irish rock band, revealed in a new interview with Times Radio that he suffers from dyscalculia, a learning disorder.

"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."

Mullen said that the diagnosis affects the way he plays music, admitting that it makes him "pained."

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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."

Dyscalculia, according to the Cleveland Clinic, is "a learning disorder that affects a person’s ability to understand number-based information and math. People who have dyscalculia struggle with numbers and math because their brains don’t process math-related concepts like the brains of people without this disorder."

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

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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.

Mullen is speaking out about his diagnosis while promoting a new documentary, "Left Behind." According to the film's website, it tells "the inspiring story of a group of determined moms who band together to create the first public dyslexic school in the largest school district in America, New York City."

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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.

According to the Irish Times, Mullen is responsible for starting U2 — at just 14, he posted a note on a bulletin board at the Mount Temple School in Dublin in 1976 that read, "Drummer seeks musicians to form band."

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.