Hypoparathyroidism is a rare condition where the parathyroid glands produce an insufficient amount of parathyroid hormone (PTH). PTH is responsible for regulating calcium and phosphorus levels in the body, so a lack of it can lead to low levels of calcium in the blood and high levels of phosphorus. Symptoms of hypoparathyroidism can include muscle cramps, twitching, and weakness, as well as tingling or numbness in the hands and feet.