Longitudinal studies showed that CSF and serum NEFL concentration were reduced and negatively correlated with motor response in patients with SMA type 1 (with 2 copies of SMN2) or in type 2 patients with short disease evolution (<6 months in one study), but not in type 2 patients with longer disease evolution [22,49,50]. Here, SMN2 is linked to spinal muscular atrophy, type 1.