NEFL and spinal muscular atrophy, type II: Interestingly, baseline concentrations of NfL in patients with SMA type 2 and with SMA type 3 were about as high as the concentrations in SMA type 1 patients after 300 days of treatment, whereas baseline concentrations in SMA type 1 patients significantly differed compared to SMA type 2 and to type 3 patients.