It is of interest to note that the ear skin tissue in WT mouse with highly abundant SMN protein is a tissue that together with the tail and hindpaws becomes progressively necrotic in SMA mice that are rescued from SMN depletion by genetic reintroduction of SMN or therapeutic upregulation of SMN [23], [24], [45], [46]. Here, SMN1 is linked to proximal spinal muscular atrophy.