WASHINGTON, D.C. ? It’s one of the grimmest threats to premature babies: Their immature intestines break down. They can’t be fed. In the worst cases, holes in the bowel let bacteria leak into the blood – and kill.

This mysterious disorder is expected to soon overtake lung disease as the leading killer of preterm infants, and researchers are struggling to figure out why it strikes and develop the first real protection.

NEC, the shorthand term for necrotizing enterocolitis, occasionally hits a full-term infant, but mostly afflicts the tiniest preemies, born smaller than 3 1/2 pounds. It starts with subtle symptoms, such as poor food tolerance.

About half of babies with severe NEC die, and survivors can face lifelong complications.

The goal: To develop drugs that can protect these fragile babies’ intestines from becoming inflamed in the first place, just as doctors now routinely give preemies lung-protecting therapies.