To confirm that poly-(glycine-proline) peptides are specifically expressed in C9FTD/ALS, synthetic peptides (GA)8, (GP)8 and (GR)8 were used as antigens to immunize two rabbits and prepared two independent polyclonal antibodies (designated anti-C9RANT) with high specificity and sensitivity for the hypothetical RAN translation product. The gene discussed is RAN; the disease is amyotrophic lateral sclerosis.