CASR and Hypercalcemia: In contrast, homozygous or compound heterozygous loss-of-function CASR mutations, or heterozygous mutations where the mother is not affected, cause Neonatal Severe Hyperparathyroidism (NSHPT), which is a severe phenotype that is associated with life-threatening hypercalcaemia, hyperparathyroid bone disease and multiple fractures.