Each different form of hyperparathyroidism has its own etiologic factors that are grouped together by type [2]:

• Primary hyperparathyroidism develops when one of the parathyroid glands malfunctions, often due to a parathyroid adenoma. Hyperplasia of the parathyroid glands, malignancy and ectopic parathyroid glands, are other etiologic factors behind this form of the disorder.
• Vitamin D deficiency or chronic kidney disease are the contributing factors behind secondary hyperparathyroidism. 
• The etiology of the third form of the disorder, tertiary hyperparathyroidism, is unknown and the condition is characterized by autonomous hypersecretion of parathyroid hormone probably due to persistent parathyroid stimulation.

When the parathyroid glands become overactive and excessively produce parathyroid hormone PTH, which is responsible for the regulation of phosphate and calcium levels in the body, it leads to hyperparathyroidism [1]. Hyperparathyroidism is divided into three forms, primary hyperparathyroidism, secondary hyperparathyroidism, and tertiary hyperparathyroidism.

It should be noted that there are other reasons for the overproduction of PTH. A person could be suffering from a glandular disorder like hyperthyroidism which leads to hypercalcemia, or there could be low calcium levels in the body due to a vitamin D deficiency or a chronic kidney disease.