Eight-year-old Justin Knight watches TV while waiting for his two-hour infusion to begin at Tuba City Regional Medical Center in Tuba City, Ariz. Knight was diagnosed with severe combined immune deficiency, a disorder commonly referred to as "bubble boy disease." In the Navajo population, one in every 2,500 children inherit SCID. In the general population, SCID is much more rare, affecting one in 100,000 children.