Parathyroid hyperplasia is the enlargement of all four parathyroid glands. The parathyroid glands are four glands in the neck that produce parathyroid hormone (PTH).

Parathyroid hyperplasia may occur sporadically (in persons without a family history of the disease) or as part of three inherited syndromes: multiple endocrine neoplasia 1 (MEN1) , MEN 2A, and isolated familial hyperparathyroidism.

In the familial syndromes, a mutated gene is passed down in an autosomal dominant fashion. That means you only need to get the gene from one parent to develop the condition.

In MEN 1, the problems in the parathyroids are associated with other tumors in the pituitary and the pancreas. In MEN 2A, the overactivity of the parathyroids is associated with tumors in the adrenal gland or thyroid. See the specific articles for more information on the causes of these syndromes.