Trends in the Timeliness of Spinal Muscular Atrophy Detection in US Infants, 2016-2023.

Screening for spinal muscular atrophy (SMA) was adopted by all US state newborn screening programs between 2018 and 2024; by the end of 2022, 48 states were screening for SMA. We assessed trends in health insurance records of SMA diagnoses to quantify improvements in the timeliness of SMA identification following the adoption of screening. We used nationally representative Medicaid claims data for approximately half of US births covered by public insurance and a convenience sample of employer-sponsored health plans. We analyzed records for birth cohorts with at least 1 full year of follow-up (i.e., through the end of the following calendar year). For 2017 births, 1.3 per 100,000 infants had SMA codes first recorded by 1 month of age; this increased to 6.6 per 100,000 among publicly insured newborns born in 2022. The rollout of SMA newborn screening across US states was also followed by improvements in the timely detection of SMA. The proportion of infants with SMA detected by 1 month increased from 18% in 2017 to 61% in 2021 and is projected to reach 75% in 2022. Growth in timely detection was even greater in the employer-insured sample. Timely diagnosis of SMA can enable the initiation of treatment prior to the irreversible loss of motor function.