Grace pulls out a rubber band wrapped around her dark brown pony tail and reveals a white patch of hair. She boasts about a Mickey Mouse-shaped discoloration on her back. Parts of her fingers and around her mouth also are lighter than the rest of her skin.

She asks her mother "how come I'm like this and nobody else is," why she's shorter than other children and says other kids make fun of her, Trujillo said.

"It's kind of hard for her to understand why kids would be mean," Trujillo said. "I just have to tell her, 'It's not your fault. Some kids are different. They think differently."'

Researchers aren't sure why some SCIDA patients never lose their baby teeth, are shorter than other children or have severe oral and genital ulcerations. One theory is that the lack of Artemis could be responsible.

As dinner trays are set down on tables for Grace, Joron, Justin and their family members who accompany them to the hospital, they are told to wash their hands.

Germs are their enemies.

While most kids are making mud pies and snow men, these children are urged to stay away from things that can trigger an infection. A fever or diarrhea could mean a trip to the emergency room.

Some 3,500 babies are delivered each year at hospitals on the Navajo Nation.

A hospital policy manual that Hu developed outlines what diseases commonly are seen on the Navajo Nation and what to do if a health provider suspects SCIDA.

"Most of us have been here for 10 years and have seen it happen," Hu said. Others, she said, "will have read about this stuff but never seen it."

Cowan said there are continued efforts to educate new doctors on the reservation about what to look for, especially because SCID is diagnosed at a much higher rate on the Navajo Nation than elsewhere.

"Even with that," he says, children "sometimes slip through."

Hu wonders whether children she has seen die would have lived if diagnosed earlier.

"Our kids who are diagnosed earlier and transplanted earlier tend to do better," she said. "Our goal is to spare families from this tragedy."