In normal conditions, production of 3 from 2 is strictly controlled by the concentrations of calcium and parathyroid hormone (PTH) in the blood, and thus the concentration of 3 in the blood is a useful indicator of functional status [2] and is helpful in the diagnosis of diseases such as hypercalcemia, hyperphosphatemia, rickets, and bone metabolism-related diseases [3,4]. The gene discussed is PTH; the disease is rickets.