Interestingly, in patients with the mutations at residue 1 or residue 56, the different available PTH immunoassays show very variable levels of serum PTH, going from below normal levels (consistent with hypoparathyroidism) to elevated levels (as in pseudohypoparathyroidism) depending on the affinity and target site of the antibody used to detect the circulating PTH (5, 20) Table 1. Here, PTH is linked to pseudohypoparathyroidism.