A high correlation between NfL in both compartments was observed (Spearman: 95% CI [0.575, 0.773], r = 0.7, P < 0.001; Pearson: 95% CI [0.955, 0.978], r = 1.0, P < 0.001; Fig. 4; correlation of SMA patient subgroups see Supplementary Figure S1). Here, NEFL is linked to proximal spinal muscular atrophy.