TD and LS provided and analysed Belgian data. FM, MS, and GB provided and analysed UK data. LS drafted the initial manuscript. LS and MS accessed and verified the underlying study data. All authors had full access to the data in the study and had final responsibility for the decision to submit for publication. LS has received consultancy fees and grants from Roche, Biogen, Novartis, Scholar Rock, BioHaven, and Zentech (Lacar). TD has received lecture fees from Biogen and Roche. MS has received consultancy fees from Roche, Biogen, and Novartis; and honoraria and support for attending meetings from Novartis and Roche. GB has received grants from Sarepta, Roche, Novartis, Pfizer, Italfarmaco, and Santhera; consulting fees from Sarepta, Entrada Therapeutics, Pfizer, Biogen, Novartis, and Roche; and honoraria and support for attending meetings from Novartis and Roche. FM has received consultancy fees from and received fees for participation in symposia for Roche, Biogen, and Novartis; has received honoraria from Biogen; has received support for attending meetings from Roche; and is on advisory board for Roche and Biogen. De-identified participant data can be made available upon request to the corresponding author by qualified investigators. The newborn screening pilot in Belgium was funded by AveXis, Biogen, Roche, the Association Belge contre les Maladies neuro- Musculaires, Minister's Office Alda GREOLI (Wallonia-Brussels Community), and donations from individuals. SMA REACH (SMA REsearch And Clinical Hub) is funded by grants from Novartis, Biogen, and Roche. There was no funding for this Correspondence.