The polymorphic clinical features associated with SOD1 mutations also underlined that SOD1 testing should be performed in all atypical motor neuron diseases not fulfilling Airlie House criteria for ALS diagnosis, especially in case of absence of upper motor neuron signs or with SMA-like presentation, or in association with sensory signs, vocal cord impairment, neurogenic bladder, facial diplegia, or gadolinium root enhancement. The gene discussed is SOD1; the disease is proximal spinal muscular atrophy.