Background: Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disease. SMA is generally categorized into five subtypes based on age of symptom onset and achieved motor milestones. In general, symptom onset and severity of SMA correlate with survival motor neuron 2 gene (SMN2) copy number.
The SMA phenotype has been evolving since regulatory approvals of SMA therapies. These therapies coupled with improvements in supportive care are leading to patients gaining motor functions that are atypical for their subtype. Due to these changes in the SMA phenotype as well as the increasing number of patients diagnosed before symptom onset due to statewide newborn screening, relying on SMN2 copy number, which will not change over time regardless of treatment, is more useful than using SMA subtypes for describing SMA clinically.
Objectives: To conduct a telephone survey with Cure SMA database members to collect missing self-reported information on SMN2 copy number and current motor function.
Results: A total of 806 respondents completed the survey out of 2807 contacts. The majority (61%) of respondents were caregivers and the majority (46%) of respondents completed a survey on behalf of someone with type II SMA. 31% of patients with type I were noted to currently sit without support and 5.1% of patients with type II were noted to walk alone at the time of the survey. 43.6% of respondents reported SMN2 copy numbers for the SMA patient. Of the individuals that did not know the copy number, 14.6% stated it was because genetic testing was not done, however, other reasons for not knowing was not collected.
Conclusions: The data from this survey will assist in future studies stratifying patients based on SMN2 copy number and current motor function due to the changing phenotypes of SMA in the era of newborn screening and effective disease modifying therapies.
Funding: Funding for this research was provided by the SMA Industry Collaboration, Genentech/Roche, Novartis Gene Therapies, Scholar Rock, Cytokinetics, and Biogen.