Hypercalcemia is the presence in the blood of an abnormally high level of calcium. There are many causes including excessive intake of vitamin D, overactivity of the parathyroid glands, and malignant disease. Malignant hypercalcemia results from the secretion by the tumor of substances (most commonly parathyroid hormone-related protein) that stimulate bone resorption or from bone metastases causing localized destruction and release of calcium into the bloodstream. Hypercalcemia may also occur as an inherited congenital condition, for example familial (or hypocalciuric) hypercalcemia or Williams syndrome.