The goal of this pilot study is to identify a marker or panel of markers in the blood or urine from a wide range of Spinal Muscular Atrophy (SMA) patients that segregates with measures of clinical severity. From this identification of candidate biomarkers, it is hoped that further investigations, both longitudinal natural history and clinical efficacy studies, will verify a biomarker with the sensitivity and specificity that will allow its eventual use as a validated pharmacodynamic marker or surrogate endpoint. In addition, this effort may elucidate biological pathways that may be potential therapeutic targets.