Although some studies reported that SMN2-FL mRNA levels are able to differentiate between patients with SMA and healthy controls and that FL-mRNA levels in peripheral blood cells inversely correlate with disease severity especially in type 1 patients (56, 57), they were not able to distinguish between different disease phenotypes (54), while some other studies found no correlation between SMN2-FL expression and disease phenotype at all (55, 58, 59). Here, SMN2 is linked to proximal spinal muscular atrophy.