A 52-year-old man presents to the outpatient clinic with a 10-year history of progressive coarsening of facial features. His wife notes that he requires larger shoes and gloves every few years. On examination, the structure marked **A** in the diagram—a prominent protruding lower jaw with new dental gaps—is evident. He also reports excessive sweating, new-onset joint pain, and recent diagnosis of type 2 diabetes. Which of the following is the most likely diagnosis?