A young college student presents tothe health clinic with symptoms of increased urination (polyuria),avid thirst and water drinking (polydipsia), and weight losswithout dieting. Significant in the family history is her fatherdeath at age 42 of what was said to be "acute diabetes." Herfather, sister and a paternal aunt also have diabetes, described asadult onset or type II. Laboratory evaluationreveals increased glucose in blood (hyperglycemia), urine(glucosuria), and urinary ketones. However, Western blotting ofinsulin species shows normal amounts of protein with a highermolecular size then usual. What is the most likelyexplanation?