Newborn Screening for Spinal Muscular Atrophy Leads to 94% Normal Motor Development With Early Gene Therapy

What Happens When SMA Is Detected at Birth and Treated Immediately?

Multiple clinical trials and real-world data registries have demonstrated that infants diagnosed with SMA through newborn screening and treated with onasemnogene abeparvovec (Zolgensma) — a one-time gene replacement therapy — before symptom onset achieve dramatically better outcomes than the historical natural history of the disease. In the landmark SPR1NT trial, presymptomatic infants with 2 copies of the SMN2 gene who received Zolgensma achieved key motor milestones: all 14 infants sat independently, and 11 of 14 (79%) walked independently. In infants with 3 SMN2 copies, 14 of 15 achieved independent walking. Broader registry data and longer-term follow-up studies have continued to support these findings, with over 90% of presymptomatically treated children meeting age-appropriate milestones on standardized assessments such as the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP-INTEND) and Bayley Scales.

The results represent a dramatic contrast to the natural history of the disease. SMA type 1, the most severe form affecting approximately 60% of cases, historically leads to progressive muscle weakness, respiratory failure, and death before age 2 in the majority of untreated children. Even SMA type 2 patients rarely achieve independent walking. In presymptomatically treated cohorts, the vast majority of infants with 2 copies of the SMN2 gene (predictive of type 1) have achieved independent sitting or walking, and very few have required respiratory support — compared to an expected rate of over 90% needing ventilatory assistance without treatment.

How Many Countries Now Screen Newborns for SMA?

The success of early treatment has accelerated the global rollout of SMA newborn screening. As of 2026, more than 30 countries have implemented universal or regional screening programs, with additional countries running pilot programs. In the United States, SMA was added to the Recommended Uniform Screening Panel (RUSP) in 2018, and all 50 states now screen for the condition. The screening test uses a simple dried blood spot to detect the homozygous deletion of SMN1 via quantitative PCR, with very high sensitivity and an extremely low false-positive rate. The screening cost per newborn is minimal, typically a few dollars added to the existing panel.

Health economic analyses have consistently found that presymptomatic treatment, despite the high cost of Zolgensma (approximately $2.1 million per dose in the United States), is cost-effective compared to the lifetime care costs of untreated SMA, which can reach several million dollars per patient including ventilatory support, wheelchairs, and full-time caregiving. Dr. Laurent Servais, a leading SMA researcher and professor of pediatric neurology at the University of Oxford, has called the combined evidence from newborn screening and early gene therapy programs among the strongest demonstrations that presymptomatic genetic screening paired with early intervention can fundamentally change the course of a previously fatal genetic disease. SMA advocacy organizations are now pushing for screening expansion in low- and middle-income countries, where the majority of affected infants are born.