The present invention relates to antibodies and related molecules that immunospecifically bind to GMAD. Such antibodies have uses, for example, in the prevention and treatment of both insulin- and non insulin-dependent diabetes mellitus (i.e. Type I and Type II diabetes) and other related disorders. The invention also relates to nucleic acid molecules encoding anti-GMAD antibodies, vectors and host cells containing these nucleic acids, and methods for producing the same. The present invention relates to methods and compositions for preventing, detecting, diagnosing, treating or ameliorating a disease or disorder, especially diabetes and other related disorders, comprising administering to an animal, preferably a human, an effective amount of one or more antibodies or fragments or variants thereof, or related molecules, that immunospecifically bind to GMAD.