[Severe neonatal hyperparathyroidism in a family with familial hypocalciuric hypercalcemia].

Familial hypocalciuric hypocalcaemia (FHH) is a rare disorder, inherited in an autosomal dominant manner. It has earlier been believed that neonatal severe hyperparathyroidism (NSHPT) is the homozygous form of FHH, but in this case story we show that it is not always like that. We describe a girl who presents with a calcium metabolic disorder from birth. Genetic examination of the girl and her family shows a single abnormal allele in the calcium ion sensitive receptor. We discuss why some heterozygotic inactivating calcium receptor mutations cause NSHPT, while the majority of other mutations only cause mild, asymptomatic hypercalcaemia as in FHH.