Jeanne Calabro's doctors can't figure out why she's still alive. She has a rare disease that disables muscles, which is particularly hard on her breathing and has threatened her life on more than one occasion.

Babies born with the illness, called acid maltase deficiency syndrome (the lack of the enzyme maltase), usually die in early childhood. The prognosis is better for adults who have the syndrome, but there are so few cases, no one knows for sure, according to Calabro's Fairfax physician, Michael Tsun.

In Calabro's case, the decline of her health has been slowed, but not halted, through experiments with her high-protein diet. She has gone into respiratory arrest four times, and suffers from diabetes.

Using crutches or a wheelchair, breathing through a tracheal tube, and occasionally dependent on a portable respirator, Calabro, who is 37, tends to her family; teaches her 13-year-old son, David, at home; tutors other young people for free; helps Loudoun County's homeless people; runs a small word-processing business; and is closing in on a graduate degree in sociology from George Mason University.

This array of activities would challenge most able-bodied adults. Yet what makes Jeanne Calabro so unusual is that, in her own world, she is just like everyone else.

Deep down, she knows that she has severe handicaps, but at any given minute she's plowing ahead with her life as if her struggles were routine. "There are times when I want to do something and don't feel well enough and get frustrated," she said. "If it means a lot to me, I'm going to do it. That's the same way with everybody . . . . I am well when I am busy."

It's lunch time and Calabro is rolling down the packed aisles of George Mason's lunchroom in her motorized wheelchair, scattering surprised students in either direction as she looks back over her shoulder to keep up a conversation.

A few hours later, Calabro is tearing along Fairfax County's tortuous Hunter Mill Road in a specially equipped van. One hand is blocking the tube protruding through her throat, allowing her to talk in bursts between deep breaths. The other hand is lurching for a cassette of folk songs. Her knees are temporarily guiding the steering wheel toward her home in Sterling.

A cherubic-looking holdover from the 1960s who loves life, learning and helping others, Calabro bubbles with enthusiasm. But there are things she can't do.

She loves to swim but can't. She wanted a large family but endured miscarriage after miscarriage. Most days about 5 p.m., her forehead droops down on her desk. She overexerts and winds up in the hospital now and again.

Calabro "works as hard as anybody, even when she's in a lot of pain," said Dorothy Moser, who advises disabled students at GMU. "She's a marvel."

About a decade ago, doctors thought Calabro had multiple sclerosis. By 1984, she was in intensive care, fighting for her life. Hospital tubes had given her an ulcer in her nose; she was told she needed a tracheal tube.

"Every day they would wheel me down the hall and open up my neck and cut away layers," Calabro said. "I didn't think I was going to live."

A few years later, a skin biopsy led to her current diagnosis, and a permanent tube was inserted in her trachea. "When they operated on me, I thought I'd never be able to talk," she said. "I was kind of worried about that."

Son David chimes in: "It's never tiring for her to talk." Mother and son share the laughter.

Calabro places an index finger over the "trake." "Everybody has limitations," she said, popping the finger off the tube just long enough for a deep breath. "To tell the truth, I don't think my abilities or situation are unusual." Another breath.

"What's unusual is my stubborn imperviousness" to indications that she can't do something. "I always make up my own mind, which is unusual in today's world . . . . I think people are afraid of limits -- what's going to happen if they go over them."

Calabro has a habit of turning a conversation about herself into one about others. It seems to be rooted in her Woodstock-generation values of helping other people improve themselves, of trying to change the world through the community-based volunteer groups she envisions as an outgrowth of her studies.

Calabro's day begins about 8 a.m. with a family breakfast like any other on her quiet cul-de-sac in eastern Loudoun County. After her husband, Michael, leaves for for his consulting job, she and David head for the study and a standard curriculum for parents who teach their children at home. (Calabro teaches David herself because she feels he responds better to individual attention.)

While David attacks long division with a pencil, she tackles the world with a computer.

"My word-processing business has diminished since I started graduate school," she said, surveying her list of morning chores: a letter to the Ruritan Club seeking money for a local youth who needs a bone marrow transplant; a reading assignment for a class; work on a newsletter for the sociology graduate student association that she has formed at GMU; several calls and errands before she reaches campus.

Once there, Calabro begins the elaborate routine of shifting from her van to her motorized wheelchair. A robotic arm swings the cart outside the van before she maneuvers into it, closes the van doors and burns rubber.

Calabro grabs lunch, returns a library book and reaches her nook in the sociology department to meet a young woman who needs help getting a high school graduate equivalency diploma.

There's no letup. Still hoarse from a long phone call about her research paper on drug prevention, she fields a late afternoon call from David and advises, "Take the meatballs out of the freezer."

Calabro scans notes before rolling to her 5:30 p.m. class on "Evolution of Social Programs." About 7 p.m., she heads back to her van to reverse the routine and head for home. She's barely parked before her dog, Lady, bounds into her lap.

Next comes making spaghetti and meatballs and eating dinner. Calabro goes through mail, gets David off to bed, sterilizes her tracheal tube and contemplates going to sleep "early -- before 12."

Her husband, Michael, 44, recalls what for him was the darkest time of their 18-year marriage: It was the 1970s; the doctors couldn't tell what was causing his wife's weakness; their son, John, died seven days after his birth.

But next came David. Michael said he has drawn inspiration and strength from his son, "and my church, and my job."

To which Jeanne Calabro adds: "and your wife."

"My work in the community is my effort to share the benefits I have: a wonderful family, a home, a desire to help," Calabro said. "Giving someone else a desire to help themselves, rather than just helping them, gives the greatest gain."