What is bubble boy disease (X-SCID)?

For almost all of his 12 years of life, David Vetter lived in a totally sterile environment, isolated from physical human contact, to protect him from the lethal effects of even the most mild infection, such as the common cold. Lacking an adequate immune system—in David's case, the ability to make T cells—the child was confined to a germ-free plastic bubble, which his parents erected in the family living room in Texas.

In 1972, when David was born with X-linked severe combined immunodeficiency (X-SCID), little was known about the condition, since no X-SCID infants had survived more than several months. When David was 12, his doctors tried to cure him with a bone marrow transplant, but sadly, David died of complications from the high-risk procedure. Subsequent research on David's blood cells identified the genetic mutation that causes X-SCID. Since then, in France and England, a few young patients with the disorder have been successfully treated using gene therapy. But there are risks to this therapy, including the development of leukemia in some patients.

Only boys are at risk for this particular inherited condition, a defect of the X chromosome. Because girls have two X chromosomes, they can carry the defective gene, but their other, healthy chromosome ensures they will not have the disease. But a boy has only one X chromosome, and if it has the mutation, he will have the disease.