CASR and neonatal severe primary hyperparathyroidism: <h4>Background</h4>In recent years, heterozygous loss-of-function mutations of the Calcium Sensing Receptor gene (CaSR) were implicated in different hypercalcemic syndromes besides familial hypocalciuric hypercalcemia (FHH), including neonatal severe primary hyperparathyroidism (NSHPT) and primary hyperparathyroidism (PHPT).<h4>Cases presentation</h4>Here we describe two unusual presentations of heterozygous inactivating CaSR mutations.