In this study, we used an in‐house ELISA method, developed and validated previously in ALS mice and patients,20, 21, 22 to quantify hyperphosphorylated (NfHSMI34) and variably‐phosphorylated (NfHSMI35) NfH levels in serum from SMA mice and from individuals affected by SMA type 2 and 3. The gene discussed is NEFH; the disease is proximal spinal muscular atrophy.