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Grand Rounds

Does Presymptomatic Treatment of Spinal Muscular Atrophy Improve Outcomes?  

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BACKGROUND AND PURPOSE: 

  • Biallelic SMN1 deletions and three SMN2 copies usually leads to the development of spinal muscular atrophy (SMA) type 2 in childhood 
  • Onasemnogene abeparvovec is gene replacement therapy  
    • Delivers SMN cDNA using an adeno-associated virus-9 (AAV9) vector 
    • Single IV infusion  
  • Strauss et al. (Nature Medicine, 2022) investigated the efficacy and safety of onasemnogene abeparvovec treatment for pre-symptomatic children with SMA type 2 

METHODS: 

  • Open-label, single-arm, Phase III study  
    • 16 sites in 6 countries 
  • Participants 
    • Infants identified with SMA through newborn screening  
    • Normal neuromuscular function who were able to swallow and breathe normally 
  • Intervention 
    • Onasemnogene abeparvovec 
  • Study design 
    • Single infusion over 60 minutes  
    • Multiple outpatient assessment visits through 24 months of age  
  • Primary outcome 
    • Independent standing, for at least 3 seconds at any visit up to 24 months of age 
  • Secondary outcome 
    • Walking independently, for at least five steps at any visit up to 24 months of age 

RESULTS: 

  • 15 children | 9 female  
    • Median gestational age at birth: 39 weeks 
    • Median weight: 3.4 kg  
    • Median age at time of molecular confirmation: 8 days  
  • At screening, all children had normal neuromuscular function 
  • Standing independently at 24 months (P<0.0001) 
    • Treatment group: 100% (14 occurred within normal developmental window) 
    • Natural history population: 24% 
  • Walking independently at 24 months (P<0.0001)  
    • Treatment group: 93% 
    • Natural history population: 21% 
  • All children survived without permanent ventilation at 14 months 
  • Maintained body weight (≥3rd WHO percentile) without feeding support through 24 months: 67% 
  • No children required nutritional or respiratory support 
  • There were no serious adverse events that were treatment-related 

CONCLUSION: 

  • For asymptomatic infants with SMA type 2, onasemnogene abeparvovec was effective and safe 
  • Most treated children were able to sit and walk independently at 24 months of age 
  • The authors state 

Given the durability of benefit observed in the follow-up study of the Phase I START trial, and the fact that motor neurons are non-dividing cells, we are optimistic that one-time treatment with onasemnogene abeparvovec will add years of independent mobility, intact bulbar function, and good health-related quality of life for children in the three-copy cohort 

Learn More – Primary Sources: 

Onasemnogene abeparvovec for presymptomatic infants with three copies of SMN2 at risk for spinal muscular atrophy: the Phase III SPR1NT trial

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Related ObG Topics:

Spinal Muscular Atrophy: Genetic Concepts and Carrier Screening 
Nusinersen: A Treatment for Spinal Muscular Atrophy (SMA) has Arrived
Another New Medication for the Treatment Spinal Muscular Atrophy is on the Horizon

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