So on Aug. 23, NiCole Robinson and Craig Snyder noticed the difference in their 34-day-old son. He was listless. His breathing was rapid and shallow.

The changes seemed innocuous, but Snyder's mind raced: It can't be. It must be. God, I hope it's not.

Doctors had told the couple that they could safely have children, even though Snyder and his first wife had lost two newborns to an incredibly rare, untreatable congenital lung disorder.

But here was Lincoln, struggling for breath. Rushing him to the hospital, Snyder felt an excruciating sense of helplessness. Thirteen days later, Lincoln was taken off life support. An autopsy confirmed that he, too, had the disorder, alveolar capillary dysplasia.

ACD, first described in the medical literature only 27 years ago, has defied study. The fact that it is so rare and so lethal has masked its hereditary forms, stymied gene-hunting techniques, and discouraged research funding. Why spend money on a disease known to have killed 114 newborns - ever?

When ACD killed Lincoln Snyder, however, it created an even rarer phenomenon - an unspeakable loss that opened the door to great gain.

Craig Snyder, 46, a lawyer and former chief of staff to Sen. Arlen Specter, is a lobbyist whose clients include hospitals and leading disease-advocacy groups such as Autism Speaks. Robinson, 35, is an actress perhaps best known for her role as Margaret on the TV show The West Wing. The couple have homes or offices (or both) in New York, Philadelphia and Washington.

Soon after Lincoln's death, they created the 3 Angels Memorial Fund for ACD Research to try to find the genetic cause.

"We're definitely draftees. We did not volunteer for this cause," Snyder said in the couple's Center City condo, a 36th-floor aerie with a sweeping view. "But if this tragedy was going to happen to anyone, NiCole and I are the best equipped to make something positive come out of it. We have the money, the network, the experience."

Snyder and Robinson fervently believe that finding the ACD gene is doable within a year. That could lead to a prenatal test, important for couples in their extraordinary situation. But it could also have farther-reaching benefits. It might reveal secrets of lung formation in the womb, shed light on common disease mechanisms, perhaps even explain some cases of sudden infant death syndrome.

At least, that's the hope.

A disease discovered

Langston, a pediatric pathologist at the Baylor College of Medicine in Houston, had autopsied the corpse of a full-term, deceptively healthy-looking newborn. In the lungs, she found some veins distorted and "misaligned." But the real problem was microscopic.

The tiniest pulmonary blood vessels - capillaries four-millionths of an inch thick, finer than human hair - were mostly missing, apparently never formed. Normally, beginning in the 16th week of fetal development, these capillaries wrap like a vine around the lung's air sacs, called alveoli. With an infant's first gulp of air at birth, oxygen seeps through the alveoli into the capillaries, then rushes into the bloodstream.

No capillaries meant no respiration. No survival.

To Langston's surprise, her paper was "a smash hit." It turned her into the preeminent - if not only - expert on ACD. Case reports from around the world began trickling in to her.

Because none of these known cases were siblings, ACD was believed to involve a spontaneous, out-of-the-blue gene mutation in the baby. Such "sporadic" mutations were impossible to predict or prevent, but at least the one that caused ACD was so uncommon it couldn't arise twice in one family.

That's what doctors told Snyder and his then-wife, Lois, after their firstborn, Rebecca, died in 1991 despite heroic measures to save her at St. Christopher's Hospital for Children in Philadelphia. They were assured that ACD - diagnosed on autopsy by a savvy coroner - could not strike again.

The next year, the Snyders welcomed the birth of Jonathan.