WASHINGTON (Reuters) - Mattie Stepanek, 13-year-old poet and advocate for muscular dystrophy patients, died in Washington on Tuesday of a rare form of the disease, a hospital statement said.

Stepanek, of Rockville, Maryland, began writing poetry at the age of three and became a national celebrity in 2001 after publication of "Heartsongs," a volume of inspirational poems.

It was the first of five books of poetry he had published and the first to be listed on The New York Times best-seller list.

"Mattie loved to be referred to as a peacemaker and a poet," the Children's National Medical Center in Washington said in a statement announcing his death.

Stepanek died of complications of mitochondrial myopathy, the metabolic muscle disease that had affected him since birth, the Muscular Dystrophy Association said in a statement.

Stepanek had served as the association's goodwill ambassador since 2002. He spoke at events across the United States and was featured on the "The Oprah Winfrey (news) Show" and CNN's "Larry King Live."

"He brightened all of our lives and he made a difference for so many people. He put a face to this cause," Stephanie Goldklang, a local MDA official said in a television interview.

"So many more people are aware of neuromuscular diseases because of Mattie," she said.