Spinal Muscular Atrophy (SMA) Biomarkers Study in the Immediate Postnatal Period of Development

Aim 1. To establish the validity of putative physiological SMA biomarkers in the immediate postnatal period. A longitudinal, natural history examination of physiological markers of muscle innervation will be performed in healthy and SMA infants. The first week of life is the ideal first time point, with visits occurring at scheduled visits up to the age two. Compound motor action potential (CMAP) amplitude and electrical impedance myography (EIM) will be examined and will be correlated with motor function. Each of these is associated with muscle innervation and provides information on the number and function of lower motor neurons in the spinal cord, the cellular target of SMA therapeutic interventions. This trial will establish the natural history of these putative SMA biomarkers as the disease evolves in affected infants. Moreover, our approach will allow for measurements in pre-symptomatic and early symptomatic subjects and determine their predictive value. Aim 2. To establish the validity of putative molecular SMA biomarkers in the immediate postnatal period. Survival Motor Neuron (SMN2) copy number is a valid, predictive molecular SMA biomarker; however, it is fixed, and therefore not useful as a biomarker of clinical progression or response to therapy. SMN messenger Ribonucleic acid (mRNA) ( and protein expression is variable in different cell types and, in mice, naturally decreases with age postnatally. In this study, SMN expression levels will be measured longitudinally in SMA patients and controls. Additional putative molecular SMA markers that have been identified to correlate with motor function will be determined in an effort to distinguish between predictive markers that change prior to development of weakness and those that change as a consequence of weakness.