FILE - RJ Mitte poses for a portrait to promote the film, "Time Share", at the Music Lodge during the Sundance Film Festival, Jan. 20, 2018, in Park City, Utah. Taylor Jewell/AP Photo/Invision hide caption

Taylor Jewell/AP Photo/Invision

LOS ANGELES — Actor and disability rights advocate RJ Mitte, who brought a lifetime of experience with cerebral palsy to fictional family struggles in an essential role on "Breaking Bad," died Monday at age 34, authorities and his representatives said.

Cameron County Justice of the Peace Cyndi Hinojosa told The Associated Press she declared Mitte dead at about 1:30 p.m. at what she believed was his home in Brownsville, Texas. She said she was unable to provide a cause, but an autopsy will be performed.

Mitte played Walter White Jr., the son of Bryan Cranston's chemistry teacher-turned-meth dealer Walter White on nearly every episode of the five seasons of the AMC show, which recently ranked as the best of the 21st century in a New York Times poll.

Cranston said he is in "deep despair" for the loss of his "sweet son."

"I met him when he was only 14 years old when he was cast as Walter White Jr., a part he played with such joy and enthusiasm," Cranston said in a Facebook post Monday night. "Born with Cerebral Palsy, he never — ever — allowed that challenge to be an excuse for anything. He met the demanding shooting schedule head on with great determination."

Mitte told the AP in 2014 that his disability and the surrounding struggles with physical therapy, family problems and exorbitant medical bills — all key subjects on the show — made him better at his job.

"You develop a different mentality and you develop a different look at how the world sees you and how you see the world," he said. "You're able to use that. And I think it's an asset instead of something that would hinder."

Mitte was born and raised in Jackson, Mississippi.

He landed small guest roles on sitcoms after moving to Los Angeles to act in 2006 before landing the role on "Breaking Bad" in 2007. The show ran from 2008 to 2013.

"That kid was pretty raw when we started shooting the pilot," Cranston said in his post, "but little by little we watched him grow into a really fine actor."

Cranston added, "I loved him, and thoroughly enjoyed being with him throughout the years on the series, and after the spotlight on Breaking Bad dimmed."

In a statement announcing his death, Mitte's representatives said he "brought authenticity to the role and built a platform on disability awareness and inclusion." The statement said he used "his platform to challenge stereotypes and promote greater representation."

Mitte's later credits included the ABC Family series "Switched at Birth" and the superhero satire series "Guardians of Justice."

He was also a producer of several independent films.

As an advocate, he served as an ambassador for United Cerebral Palsy and Shriners Children's. He was also president of his own Mitte Foundation supporting philanthropic and community initiatives around disabilities.