Finally, we showed that SMN protein could be readily detected in exosomes isolated from mouse or human serum (Figs 6 and 7), and that the quantity of SMN protein contained in the serum-derived exosomes was reflective of the genotype, or disease state, in a mouse model (Fig. 6) and in patients (Fig. 7) with SMA. This evidence concerns the gene SMN1 and proximal spinal muscular atrophy.