"We never thought anything like this would happen to us. In my heart, when I heard that result, we thought, 'No, he's a healthy baby,"' Redhouse said. "He just didn't look like he had SCID. People would say to us, he's not losing weight, he doesn't have skin rashes."

Bone marrow transplants can be a lifesaver for children who suffer from SCIDA, providing them with stem cells that take root and begin producing T cells. But even with the best care, not all children will be saved.

Shortly after receiving a transplant this summer, baby Sean's cells are growing "just a little bit," Redhouse says, but it could be months before he can return to his home in Farmington, N.M., on the edge of the Navajo reservation.

"He has to have a certain number before he gets to go," said Redhouse.

At clinic each week, doctors weigh baby Sean, take his temperature, blood samples and check for any rashes, changes in behavior or sleeping patterns.

Because SCIDA patients lack the Artemis gene, Cowan and his team have decided not to prep the patients for bone marrow transplants using the standard approaches, such as radiation or chemotherapy, which break down DNA in order to rebuild the immune system.

"It turned out that was extremely dangerous for the Navajo SCID babies," said Jennifer Puck, who studies inherited immune deficiency disorders at UCSF. "In fact, many of them died before the transplant could be given to them because of the toxicity from the radiation treatment."

On a recent day at the Tuba City Regional Medical Center, 8-year-old Justin Knight is playing with action figures as he awaits a bimonthly reunion with two other SCIDA patients.

Inside the infusion room, Trujillo's 9-year-old daughter, Grace, rants about her favorite sports, how much she likes math and what she has learned from having SCIDA nearly a decade after being diagnosed.

"Take medicine and eat the right food," she jokingly says, holding up a candy bar. "Chocolate keeps me going."

A chair opens up nearby, and Justin enters the room.

He and fellow boarding school classmate Joron Mike stare up at the TV, seemingly oblivious to everything else.

Grace and the boys each have a port-a-cath, a direct conduit to a major blood vessel — implanted in their chest. Prolonging their lives is a two-hour infusion of gamma globulin to reinforce their B cells. Once diagnosed with SCIDA, most patients at the Tuba City hospital are sent hundreds of miles from their homes on the reservation to UCSF Children's Hospital to undergo transplants.

"These kids just didn't happen to fully take with the bone marrow," said Mary Schillo, an infusion nurse at the hospital. "They will have to do this for the rest of their lives."