Happy to have given birth in January 2015 to two seemingly healthy boys, Levi and Colton, after an uneventful pregnancy, Kala Looks gave little thought to the routine heel prick of newborn screening. At 23 and 24, she and her husband, Phillip, were high school sweethearts starting a family.

Two weeks later, a Michigan state health official called. Something came up on Levi’s screen. You need to bring him in right away. Three weeks and numerous blood draws later, the Looks had a diagnosis: Severe combined immune deficiency (SCID) — “bubble boy” disease. Levi’s blood had only a few T cells, crucial ingredients of the immune system, and those were likely his mother’s lingering cells. Soon he would have no immune system at all.

That the fraternal twins are now healthy, active toddlers, climbing onto the dining room table and leafing through picture books and starting to talk, is thanks to newborn screening and a pioneering gene therapy trial at Dana-Farber/Boston Children’s Cancer and Blood Disorders Center.

Had Levi been born before October 2011, when Michigan began screening all newborns for “bubble boy” disease, he could well have died of overwhelming infection before his first birthday.

Instead, Levi has a functioning immune system after being treated in Boston as part of an international clinical trial of gene therapy for boys born with X-linked SCID. He is one of three boys treated on the trial’s U.S. arm whose disease was picked up by universal newborn screening, now standard in 42 states. Of the other four boys treated at U.S. sites, one from South America was diagnosed at birth, because an older brother had died of the disease. Three boys, from South America or states that didn’t yet have newborn screening, were diagnosed after suffering life-threatening infections that their bodies had trouble shaking. …