MEN1 and pancreatic insulinoma: However, primary hyperparathyroidism was the most prevalent manifestation (75%) among young patients in a cohort of 924 patients with MEN1, followed by pituitary adenomas (34%) and pancreatic neuroendocrine tumors (34%), with the majority of the latter not being functional.2 In this reported case, hypoglycemia, secondary to insulinoma, was the first clinical manifestation.