Baseline NfL values in both body fluids, CSF and serum, of the 18 SMA patients before the initiation of nusinersen treatment (first dose, month 0) were significantly higher within the group of patients with 2 SMN2 copies than in those with >2 SMN2 copies (95% CI; CSF [3855, 23541], serum [327, 1019], P < 0.001; Fig. 2A and B). The gene discussed is NEFL; the disease is proximal spinal muscular atrophy.