Absolute quantification of full length SMN transcripts will be performed. The SMN1 and SMN2 transcripts will be measured in a multiplex reaction and SMN-del7 will be quantified separately. Droplet digital PCR will be used to determine SMN levels to further increase reliability and reduce variance in the SMN mRNA level determination. SMN protein in PBMCs SMN cell-based immunoassays will be performed. This assay is performed using a single monoclonal antibody for SMN and does not involve the disruption of cells. From the same PBMC sample, a commercially available SMN ELISA will also be performed according to the manufacturer's instructions. The B for SMA pilot study identified over 100 protein analytes that significantly correlated with motor function in SMA patients compared to controls.