Here, we report a 3-generation FHH1 kindred with a novel loss-of-function CASR mutation (p.Ser448Pro), in which an affected mother, who was heterozygous for the CaSR mutation, had 4 children, 2 of whom had asymptomatic hypercalcemia in association with the heterozygous CaSR Ser448Pro mutation, 1 without a CaSR mutation was normocalcemic, whereas another, also without a CaSR mutation, had hypocalcemic seizures as a consequence of transient neonatal hypoparathyroidism. The gene discussed is CASR; the disease is hypoparathyroidism.