P1.203: Electrodiagnostic assessment of newborn screen positive spinal muscular atrophy babies

Background: This study aims to investigate the potential utility of compound muscle action potential (CMAP) amplitudes and cumulative motor index (CMI), a sum of multiple motor CMAP’s, as biomarkers for assessing disease severity in neonates with spinal muscular atrophy (SMA) identified by newborn screening (NBS) and confirmed by genetic testing.

Methods: We conducted a retrospective review of 21 SMA newborns (2SMN2 copies n=11, 3SMN2 copies n=10, girls n=10, Caucasian n=11, African American n=8). Assessments performed at the median age of 16 days (IQR 13, 28 days) included weight (kilograms, Kg), right median, ulnar and fibular motor nerve CMAP amplitudes (millivolts, mV) and functional scores of Children’s Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP-INTEND).

Results: The analysis revealed notable findings with statistically significant difference in the motor CMAP amplitudes for the right median (2.6 vs. 3.8 mV, p 0.004), ulnar (2 vs 6.4 mV, p 0.007), fibular (2.1 vs. 4.05 mV, p 0.007) nerves and CMI (7 vs. 14, p 0.004) between 2 vs. 3 SMN2 copy number babies. Those differences in weight (3.83 vs. 4.13, p 0.44), and CHOP-INTEND scores (46 vs. 54, p 0.09) were insignificant.

Conclusion: We advocate for electrodiagnostic testing to be included in the initial assessment of SMA babies as the results inform the treating physician about SMA disease severity while awaiting confirmatory genetic testing and SMN2 copy number. Furthermore, the readily available electrodiagnostic test results expedite insurance approval for gene replacement and modifying therapies, which have shown to improve outcomes.