SMA Birth Prevalence in US Lower Than Expected, New Report Finds

Newborn screening (NBS) measures have continued to estimate the prevalence of spinal muscular atrophy (SMA), and the latest data is that the prevalence of infants born with SMA in the US is lower than the historic global SMA birth prevalence estimated, according to a study in JAMA Pediatrics.¹

Globally, SMA is diagnosed for an estimated 1 in every 10,000 births | image credit: Ilgun - stock.adobe.com

Previous investigations revealed that SMA is diagnosed per every 1 in 10,000 births worldwide.¹ NBS was used more broadly following recommendations for the practice that were voiced by the American College of Obstetricians and Gynecologists (ACOG) and the American College of Medical Genetics. In 2019, ACOG had recommended that NBS be a mandatory state-based public health program for all newborns that parents could opt out of.²

More prevalent use of NBS has enabled researchers to collect more widespread, precise data on SMA. To provide up-to-date statistics on the birth prevalence of SMA and the dispersal of the SMN2 gene throughout newborns with SMA in the US, public health laboratories across 30 states collaborated with Cure SMA—an advocacy organization based in the US—to gather information from infants with SMA who underwent screening prior to their diagnosis.

Between October and December 2021, the present authors’ data were obtained through online surveys, individuals who directly volunteered information with Cure SMA, or the websites of the states’ public health departments.

The 30 states included in this analysis gave the researchers data on 6,244,825 infants. Of these infants, there were 425 who were confirmed to have SMA. Therefore, they estimated that every 1 per 14,694 newborns has SMA in the US. In addition to this information, 21 states provided statistics for the number of SMN2 copies carried by newborns (n = 240) with SMA. This part of the analysis revealed that 5% of infants had a single copy of SMN2, 49% had 2 copies, 33% had 3 copies, and the remaining 13% had at least 4 copies. The authors added that around 5% of individuals with SMA have a single-nucleotide variant of the SMN1 gene; however, this mutation cannot be uncovered with NBS and therefore this figure not included in the estimates of the birth prevalence of SMA.

NBS holds a lot of value when it comes to the management and treatment of SMA. As noted in another 2024 investigation published in JAMA Pediatrics, infants with SMA that underwent NBS had significantly better outcomes compared to an unscreened group.² A total of 234 children were included in this study and assigned to either a NBS cohort (n = 44) or non-screened, clinical symptom onset cohort (n = 190). Those in the NBS cohort received disease-modifying treatment much earlier on average (1.3 months vs 10.7 months), and 90% of NBS infants (n = 40) achieved the milestone of independent sitting compared with 74.2% (n = 141) of those in the clinical symptom onset group. Furthermore, of these infants, independent ambulation was achieved in 63.6% (n = 28) in the NBS cohort compared with 14.7% (n = 28) of those in the clinical symptom onset cohort.

With the literature on SMA indicating the benefits of earlier treatment interventions, NBS and the collection of this data could be utilized to predict the health care resources that should be dedicated to SMA, as well as aid in the planning of future research, treatment, and care.

References

1. Belter L, Taylor JL, Jorgensen E, et al. Newborn screening and birth prevalence for spinal muscular atrophy in the US. JAMA Pediatr. 2024:e241911. doi:10.1001/jamapediatrics.2024.1911

2. ACOG Committee. ACOG Committee opinion no. 778 summary: newborn screening and the role of the obstetrician-gynecologist. Obstet Gynecol. 2019;133(5):1073-1074. doi:10.1097/AOG.0000000000003246

3. Schwartz O, Vill K, Pfaffenlehner M, et al. Clinical effectiveness of newborn screening for spinal muscular atrophy: A nonrandomized controlled trial. JAMA Pediatr. 2024;178(6):540-547. doi:10.1001/jamapediatrics.2024.0492