Abstract: Recombinantly manufactured fusion proteins comprising a HERV-K (HML-2) Env protein fragment or an analog thereof linked to a human Fc fragment are described. The fusion proteins may be administered to patients having a disease or a disorder with the intention of mitigating and/or reducing the duration of symptoms associated with the condition or disease (for example but not limited to muscular weakness, paralysis and respiratory failure), and/or preventing symptoms associated with the condition or disease, for example, by preventing motor neuron degeneration and cell death in amyotrophic lateral sclerosis (ALS) patients associated with the condition or disease. Improvement after treatment may be manifested as a decrease or elimination of such symptoms, for example, by a decrease or elimination of symptoms associated with ALS, and/or by a decrease in the duration of such symptoms.