Is growing up in sunny San Diego a guarantee of a cheerful disposition? You might think so, from meeting radiant, smiling 16-year-old Amanda Van-Benthuysen, known to family and friends as Mandy.

But for Mandy, looking on the bright side hasn't always been easy. By the time she was 4 and 1/2, Mandy's parents, Thom and Ginny, were so concerned about her peculiar, waddling gait that they took her to Children's Hospital in San Diego for an examination. Mandy received a diagnosis of limb-girdle muscular dystrophy.

Cory, Mandy's older sister by six years, remembers: "When she first started elementary school, it was very difficult because the kids didn't understand what she had, why she wore leg braces and why she walked so funny." Cory, who has always looked out for her sister's emotional well-being, once went to Mandy's school to stand up to a bully who had been teasing her.

Mandy recalls feeling frustration as she watched friends running and playing. "I always felt kind of hurt because I could usually do those things, but I'd be so slow, and I'd tire out fast. I'd feel almost like a failure."

That feeling gradually faded away, partially with the help of a physical therapist who educated Mandy about ways of dealing with her disease and keeping her muscles as strong as possible.

Another positive factor was MDA. Once, when 8-year-old Mandy was attending MDA clinic, she was asked if she'd be interested in representing the Association as a goodwill ambassador.

Mandy said yes, and over the next few years she attended bowl-a- thons and other MDA events in the San Diego area, then throughout California. Speaking on behalf of MDA made her more articulate about muscular dystrophy and the need to fight back against it. Instead of feeling bad about being different from other kids, she began to feel pride and satisfaction in the work she was doing.

This new confidence helped Mandy find friends who see her for what she is: a beautiful, fun-loving teen-ager who cares a lot about other people. She was voted homecoming princess her freshman year in high school.

Mandy, now in her junior year, can walk unassisted for long periods, although she has a wheelchair which she has begun using more frequently. She recently learned to drive, a skill she uses every day to get to school and back.

Mandy and her friends like going to juice bars, health clubs and drive-in movies. One of their favorite school activities is "air band" -- a pantomime skit performed in front of an audience and done in synch to a popular musical recording.

Mandy and her family appeared in a video profile on the 1996 Jerry Lewis MDA Labor Day Telethon, and then came out live for a follow-up interview. Speaking candidly with Telethon co-host Jerry Springer, Mandy admitted she was angry that muscular dystrophy had made it necessary for her to make such a video in the first place.

She praised MDA not only for seeking a cure but also for "trying to help me through my life before that cure."

Shortly after the Telethon, Mandy was offered the position of MDA National Youth Chairperson for 1997, a role that will take her across the country meeting with youth organizations that raise funds for MDA. Mandy will also participate in MDA publicity campaigns and appear on next year's Telethon to greet and thank high school and college campus representatives.

Mandy is eager to take on this new role for MDA. Like her loving parents and sister, she's a firm believer that research will yield the answers needed to defeat neuromuscular diseases.

"As far as a cure goes, I know there will be one," she says. "I've always believed that. I hope other people will help and contribute to make it happen."