Aim 2. To establish the validity of putative molecular SMA biomarkers in the immediate postnatal period.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 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.