Back in the nursing home, John Philip Mattingly, one of the oldest and most seriously afflicted members of the family, sips ice water and recalls, in a raspy voice, the lineage of his illness.
"My father had it," says the 72-year-old former bacteriologist with the state Department of Agriculture. "He was in a wheelchair for 25 years. Dad had five brothers, and two of them had it."
As a boy, John Philip often stumbled and fell. As he reached manhood, his feet and hands began to weaken. For years, he thought his problems were the result of a childhood bout with scarlet fever.
He didn't discover until he was middle-aged that his slow-motion tumble into paralysis was part of the Mattingly family legacy. "In those days, we did not know anything about this condition," he said. "It really was a mystery."
Mr. Mattingly's cousin, Anna Mae Wuenschel, sits in a wheelchair, pushed by her husband.
Over the past two years, the 72-year-old retired State Department employee has broken her right hip and her right leg in separate falls at their Silver Spring condominium.
When she was 35, she thought the weakness in her joints was arthritis. By the time she was 53, in 1975, she was tripping every afternoon.
The State Department sent her to the NIH for treatment. Doctors there didn't realize that she was a member of the extended Mattingly clan. They couldn't find anything wrong.
About five years ago, she was told she had the same disorder as her cousin, John Philip Mattingly. And, she discovered, her son had it as well.
She wishes there had been a test when she was younger.
"I would want to know," she said. "If I'd have known I had this, I would have traveled more. I love to travel."
There was one thing she would not have done.
"I would not have had children," she said. "I don't think it would be fair. It's bad enough now, the way the family is, without passing it on further."
Bonnie Mattingly Beardsley, who is now 46, sees things differently.
One day in 1974, she drove to the NIH. The same neurologist who diagnosed her father, John Philip Mattingly, asked her a few questions and watched her flex her ankles. He quickly confirmed her fear: She had the same genetic ailment. She was five months pregnant with her first child.
L "I teared up and said, 'What about my baby?' " she recalled.
A 50-50 gamble, the doctor said. "Do you want this baby?" he asked.
"I do very much," she said.
"Then go home and have a happy baby, and what comes, comes," he said.
Her toddler, Nick, looked "fat, round, happy, healthy," she said. But she noticed he couldn't stand from a squat without pushing off with his hands. Her doctor confirmed her fear: He had the Mattingly disorder.
All his life, she said, Nick has been willing to struggle. He struggled to wrestle in junior high school, and failed. He struggled to become an actor, and succeeded.
Today he is enrolled in a Florida college, spending the year in London in an acting program.
Ms. Beardsley never regretted her decision to have Nick. Later she gambled and had another child, a daughter, who was not affected.
"It comes back to the basic premise that, just because everybody doesn't walk the same, their life is still valuable," she said.
"I wish I didn't have" the disorder, she said. "I wish my son didn't have it. It bothers me a lot. I'm starting to feel my world is limited by it, and that really bothers me, bugs me, irritates me.
"But I'm still glad I'm here."
DOUGLAS BIRCH is a reporter for The Sun.