Immediate testing can save newborns.

• Position: Immunodeficiency

A newborn screening test for severe combined immunodeficiency (SCID) reliably identifies infants with this life-threatening inherited condition, leading to prompt treatment and high survival rates, according to a study led by Jennifer Puck, pediatric immunologist at Benioff Children's Hospital at the University of California, San Francisco, who also found that SCID affects approximately one in 58,000 newborns, indicating that the disorder is less rare than previously thought. (Previous data indicated it affects one in 100,000 babies.)

SCID is a group of disorders caused by defects in genes involved in the development and function of T cells and other infection-fighting immune cells. Infants with SCID are highly susceptible to life-threatening infections. SCID is fatal, usually within the first year or two of life, unless affected infants are given immune-restoring treatments, such as transplants of blood-forming stem cells or gene therapy. More than 80% of affected infants do not have a family history of the condition.

The SCID newborn screening test measures T cell receptor excision circles (TRECs), a by-product of...