Very low magnesium levels can cause hypocalcemia by PTH resistance or by preventing PTH release. Serum calcium levels regulate the secretion of parathyroid hormone from the parathyroid gland, but serum magnesium levels could do the same. Low serum magnesium levels can stimulate the secretion of parathyroid hormone, but very low magnesium levels could block the secretion. This block could cause severe hypocalcemia in severely hypomagnesemic patients. The gene discussed is PTH; the disease is Hypocalcemia.