After her younger brother was diagnosed with a deadly mitochondrial disease, Makenzie Lawrey had an idea about how to help him: She would make him a superhero.

Makenzie Lawrey, 9, wrote a book inspired by her younger brother, Gavin, called "The Mighty Mito Superhero."

Gavin, 6, suffers from mitochondrial disease which leaves him with seizures and tremors, in addition to pulmonary problems. In her book, Makenzie lets Gavin, "the Mighty Mito Superhero," have the strength to handle doctor visits and his disease while "teaching those around him" about perseverance.

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The United Mitochondrial Disease Foundation describes the disease as being caused by defects in the mitochondrial DNA the result in the cells losing energy and eventually dying. Symptoms can include loss of motor control, muscle weakness and pain, gastro-intestinal disorders or difficulty swallowing.

There is no known cure.

Brandie Lawrey, Makenzie and Gavin's mother, said that Makenzie often worries about her little brother and is determined to raise $1 million for research into mitochondrial disease and to find a cure for her brother.

"I said, 'Do you know how much that is?'" said Lawrey of the million-dollar goal. "I said 'How about $10,000?' And she said, 'No mom I want to raise $1 million. Finding a cure will take a lot of money.'"

By selling the book on Amazon, Lawrey said her daughter had already raised more than $20,000 for medical research.

But this isn't even the first time Makenzie has raised money to help her brother. Nearly two years ago she raised thousands of dollars on an online campaign, after a family friend helped to set it up, to buy a service dog for her brother.

Now the family has a small black poodle named Hershey that helps comfort Gavin, when he's in pain.

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Makenzie Lawrey made a superhero book in honor of her younger brother Gavin. (WZVN)