At an age when many teens tend to feel self-conscious about their appearance, Cahill says he doesn't mind that his YouTube channel makes him an easy target for criticism.
"I've seen all the hurtful comments and you just have to learn to not let anyone get you down about the disease," said Cahill. "I just really don't care what they say."
Barbara Wedehase, the executive director of the National MPS Society, which is the umbrella organization for all mucopolysaccharidose disorders, including Maroteaux Lamy Syndrome, said that other people suffering from rare diseases might be inspired by Cahill's outgoing personality.
"He's 15 and that's an age where people are really scrutinizing their body and looking at other people very closely," Wedehase said. "And to have someone else out there advocating for them just means so much."
The power of the Internet for sufferers of rare disorders should also not be overlooked, she said.
"It's not unusual that a child with a rare disease such as this may be the only child in their community with this disease," Wedehase said. "But to be able to look at Keenan ... he's a terrific role model and can help others with their self-esteem."
But when it comes to inspiring others, Cahill is modest when asked what he'd like to tell other kids facing similar challenges.
"I'm not sure," said the teen. "I think I'd just say to them, don't care what other people think and remember that you're your own person."
"People don't have the right to say, 'hey, don't do this, you can't do this,'" he said. "No matter what people have, they can do anything."