PTH and primary hyperparathyroidism: These polymorphisms were studied in patients with primary hyperparathyroidism, but no overall association was found,[28–30] although 1 study showed a correlation between rs1801725 polymorphism and a higher PTH level in normocalcemic hyperparathyroidism patients.[31] The expression of the CaSR was found to be higher in patients with ESRD carrying the rs1042636 and 1801726 homozygous genotypes for the minor allele,[53] while the rs1042636 major allele homozygous genotypes seemed to be associated with the responsiveness of the parathyroid gland to changes in extracellular Ca2+52.