PTH and Hypercalcemia: All carriers of the CDKN1B variant with available measurements of calcium and PTH levels had mild, asymptomatic hypercalcemia due to primary hyperparathyroidism (measurements were not available in one case), with levels of ionized calcium concentrations ranging from 1.33 to 1.50 nmol/L and PTH concentrations between 2.5 and 12.0 pmol/L (Table 1).