Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Primary Hyperparathyroidism ?
    ### Response:
    In about 80 percent of people with primary hyperparathyroidism, a benign, or noncancerous, tumor called an adenoma has formed in one of the parathyroid glands.2 The tumor causes the gland to become overactive. In most other cases, the excess hormone comes from two or more overactive parathyroid glands, a condition called multiple tumors or hyperplasia.
    