(CNN) -- With a twinkle in his eye and a gentle smile under the wide brim of a black cowboy hat, Clint Black is still out on the road charming country music fans of all ages. But beyond performing the hits like "When I Said I Do" and "Like the Rain," his music now has a mission. Black makes time out on the road these days for greeting very special fans -- families and children suffering from Rett syndrome. The rare disease is something Black and his family are all too familiar with.
"My niece Courtney, my brother Kevin's daughter, was afflicted with and lost her battle with it at age 16," Black said.
Rett syndrome is a rare genetic disorder that affects the way the brain develops. It is almost exclusively found in girls. According to Barry Rinehart from the International Rett Syndrome Foundation, Rett's is on the far end of the autism spectrum and is a mutation of the X chromosome, which is why it mostly affects girls.
"Essentially, something is happening in the human body where the brain and the nerve endings aren't making that connection. So that affects their breathing, that affects how they use their hands, that affects all kinds of communication things. You see all these girls who want to communicate and they probably are communicating but we aren't paying attention in the way we should be paying attention. But also they'll have seizures. They often won't be able to walk, so it manifests itself in different ways. So for some women and girls it can be very severe and lead to death. You know (it has a) 20% mortality rate but other times it can express itself very mildly," said Rinehart.
Unfortunately for the Black family, Clint's niece fell into the 20th percentile. But he felt that this tragedy was a call to action.
"I never really knew what I could do, but once I saw my brother trying to help and doing some fundraising, I got involved and we started holding annual golf tournaments and concerts and I went on "Apprentice" and raised $20,000," Black said.
While competing on "The Apprentice," fellow contestant Scott Hamilton vowed to help Black raise more money.
"He acquired a grant from the Pioneer Fund for a million dollars -- a matching grant. So we raised our million and the Pioneer Fund matched it and then some," Black continued.
Black now serves as the honorary chairperson for the Research to Reality campaign for the International Rett Syndrome Foundation. He's the face of the campaign, but the music star is rather humble about his influence.
"I don't want to pretend I'm doing a great deal, you know I try to bring attention to it. I do these fundraising events. There's so many people working so much harder behind the scenes and I really even personally have no idea -- I have a sense -- of how much goes into it."
But Rinehart said he feels very differently about Black's contribution toward finding a cure.
"Rett syndrome is a rare disorder and because of that, a lot of people have never heard of it. And that's a challenge for us," Rinehart said. "So when someone like Clint Black comes along and who is willing to take something that is honestly really private and painful for their family, and to have the courage to come public about that, and be an advocate for us, and talk about our progress, and talk about the hope that we have -- that's very encouraging."
Rinehart continued, "Our hope is it (Rett's) will become a household name ... so we'll be able to spot someone with Rett syndrome and direct them to help."
Rinehart said a lot of assistance is available for girls with Rett's, and Black's help is measurable because "more people are giving and more research is possible because of that, and that gives a lot of hope to a lot of families."
These women and girls, who Black calls "Rett's Angels," lack the ability to communicate verbally, so he is devoted to raising his voice for them.
"I think the human, knee-jerk reaction is to look away. Because it's really hard to see ...but the more I see, the more I see the families and how hard they fight, the more I realize we, we can't look away, we have to look. We have to see."
"And I tell myself when I'm looking at these children that these are the divine among us. They're the ones that have been given the hardest paths. And so I feel like it's a real privilege for me to come in contact with them. And that's how I deal with it emotionally."
"I remember seeing an interview with someone a long time ago who had a near-death experience, and said she had been visited by angels," Black said. "And she was told that those with the hardest paths are the most divine. That they chose the hardest paths to help those around them. So that stuck with me. So when I'm meeting a family who's really suffering with this and see the child, that's the perspective I choose to have."