By injecting siRNA intramuscularly for delivery to spinal motor neurons through retrograde transport of adeno-associated virus (AAV), one study demonstrated a substantial decrease in SOD1 and a subsequent functional impact, namely a delayed loss of grip strength, in the SOD1G93A mouse model of ALS, providing proof of principle for the selective reduction of any neuronal protein and supporting intramuscular injections of siRNA for fALS [9]. This evidence concerns the gene SOD1 and amyotrophic lateral sclerosis.