A 28-year-old man presents with recurrent nephrolithiasis and refractory peptic ulcer disease. Vital signs are stable (BP 128/82, HR 88, RR 16, Temp 37°C). Laboratory studies reveal hypercalcemia (10.8 mg/dL), elevated fasting gastrin (450 pg/mL), and normal glucose (95 mg/dL). Serum PTH is elevated. MRI brain demonstrates a 1.2-cm pituitary lesion. He denies thyroid symptoms. Which gene is most likely mutated in this patient?

1. A)TP53 tumor suppressor gene
2. B)NF1 tumor suppressor gene
3. C)MEN1 tumor suppressor gene encoding meninGABARITO
4. D)VHL tumor suppressor gene
5. E)RET proto-oncogene