SMN2 and proximal spinal muscular atrophy: Analysis from the NURTURE study demonstrated significantly elevated levels of pNfH in both plasma and CSF of presymptomatic infants with SMA compared to healthy controls (geometric mean plasma pNfH: 1090.8 pg/mL in controls; substantially higher in SMA), with markedly higher concentrations observed in infants with two versus three SMN2 copies (plasma: p = 0.0050; CSF: p = 0.0020) [49].