SMA patients with >2 SMN2 copies aged between 1 and 17 years exhibited a median sNfL level of 10.42 pg/mL (range: 4.29–34.50 pg/mL, n = 13), which is two times higher (95% CI [1.990, 6.880], P < 0.001) than the median of their age‐matched controls (4.65 pg/mL, range: 1.84–12.00 pg/mL, n = 52). Here, SMN2 is linked to proximal spinal muscular atrophy.