In a small number of patients, primary hyperparathyroidism is associated with other endocrine syndromes. This occurs in two familial syndromes, MEN type I and type II. The former type is associated with hypersecretion of hormones of the pituitary (growth hormone or prolactin, usually), islet cells of the pancreas (usually insulin or gastrin secreting), and the parathyroids. In MEN type II, patients develop medullary carcinoma of the thyroid associated with phaeochromocytoma. Primary hyperparathyroidism occurs in a minority of patients. Both of these MEN syndromes are inherited as autosomal dominant conditions, but hyperparathyroidism is not expressed in either before the age of ten.
