The absence of elevation of NfL, despite a chronic injury process of spinal motor neurons in SMAJ (1), contrasts with high levels of neurofilaments, both NfL and pNFH (phosphorylated neurofilament heavy), in blood and CSF of patients with ALS (24, 25), and in children with recently diagnosed 5q-SMA (26, 27). Here, NEFH is linked to amyotrophic lateral sclerosis.