Methods for treating and/or limiting development of diabetes in a subject with amyotrophic lateral sclerosis (ALS) by inhibiting IgG-mediated activation of voltage-gated calcium channels (VGCCs) in cells of the subject, by one or more of removing IgG from blood of the subject, blocking IgG from activating VGCCs in the subject; or blocking VGCCs in the subject are described, as are methods for identifying ALS patients at risk of developing diabetes.