MEN1 Syndrome MENIN 11q Autosomal Dominant

A 32-year-old man presents with recurrent nephrolithiasis, severe peptic ulcer disease refractory to high-dose proton pump inhibitors, and hypogonadism. Laboratory studies show hypercalcemia (12.4 mg/dL), elevated PTH (185 pg/mL), and fasting gastrin >1000 pg/mL with secretin-stimulated rise. MRI brain reveals a 1.2 cm prolactin-secreting pituitary macroadenoma. Pancreatic MRI shows multiple hypervascular neuroendocrine lesions. His father died of metastatic gastrinoma at age 48, and his paternal aunt had primary hyperparathyroidism with insulinoma. Genetic testing confirms a pathogenic truncating mutation in the gene located at the locus marked **B** in the diagram. Which of the following best describes the molecular consequence of this mutation?