American Indians typically have had a higher infant mortality rate than other ethnic groups because of poverty and limited access to medical care, said Dr. Diana Hu, chief pediatrician on the 27,000 square-mile Navajo Nation. So when an infant died of infection, "you don't really notice that is odd," because others also were dying of infection, she said.

Things changed in the late 1970s and early 1980s with improvements to health care.

"This is not just kids dying, this is something odd," Hu recalls thinking. "When you start to lower your infant morality (rate), you start to notice when kids die."

But detecting the disorder wasn't easy. What can frustrate parents are that the symptoms of SCID aren't much different from the common cold or flu. Normal kids can have numerous ear infections in a year but are treated with antibiotics and the infection goes away.

In SCID patients, the infection lingers and worsens.

Researchers have identified about a dozen genes that cause SCID. Cowan, director of the Pediatric Bone Marrow Transplant Program at the University of California-San Francisco, argues that Navajos and Apaches suffer from the most severe form of the disorder in which they lack a gene called Artemis. Without it, the children's bodies aren't able to repair DNA or develop disease-fighting T cells and B cells.

"These kids are the most difficult to treat," he said.

The autosomal recessive gene found in the Navajo and Apache populations can be passed from one generation to the next without harm. But when two people who carry the gene have children together, there's a one in four chance their children will be born with SCID. The type seen in the Navajos and Apaches is known as SCIDA because the two groups share a common language root, Athabascan.

The disorder is something Lynnae Redhouse and Sean Frank, a young Navajo couple, never had heard of.

Day after day, their son, also Sean Frank, would cough until he turned blue and sleep more than a baby should. His hands and feet shook, and soon after he was fed, the milk would come right back up.

Redhouse and Frank knew it was normal for a child to occasionally get sick, but something here wasn't right.

"It turned into just a routine of waking up all the time for him because we were so worried he wouldn't wake us up at all," said his father.

Each time Redhouse and Frank would seek care for their son, the message was the same: Take him home, he's fine, doctors told them.

It turns out he wasn't fine, and not until the child was taken to the University of New Mexico Hospital in Albuquerque did his parents find out their son has SCIDA.