Hypercalcemic diseases can derive from loss-of-function CaSR mutations, such as type 1 familial hypocalciuric hypercalcemia (FHH1) and neonatal severe hyperparathyroidism (NSHPT) (Chattopadhyay and Brown, 2006; Hannan et al., 2012; Hannan and Thakker, 2013; Hannan et al., 2016), while gain-of-function CaSR mutations are associated with hypocalcemic disorders, such as type 1 autosomal dominant hypocalcemia (ADH1) and type 5 Bartter syndrome (Vargas-Poussou et al., 2002; Chattopadhyay and Brown, 2006; Hannan and Thakker, 2013; Hannan et al., 2016; Hannan et al., 2018). Here, CASR is linked to neonatal severe primary hyperparathyroidism.