These syndromes have been mentioned in the discussion of certain tumors that may be associated with MEN. These syndromes are familial, with types I and II being inherited as an autosomal dominant disorder. About one half of type III cases are sporadic. Some cases of incomplete or overlapping organ tumor patterns have been reported.

Although carcinoid tumors are not considered part of the MEN syndromes, carcinoid of foregut origin (bronchial and gastric) may be associated with MEN I. Gastrinomas of the Z-E syndrome may be associated with MEN I, which includes pancreatic islet cell tumors (these tumors may produce insulin, gastrin, or vasoactive intestinal polypeptide). About 5%–10% of pheochromocytomas are associated with MEN types II and III.

Many patients with the MEN syndromes do not have all the tumor types considered part of the syndromes.