CASR and hyperparathyroidism: Whilst FHH1 [OMIM #145980] is thought to be a benign, typically asymptomatic condition (8), transient neonatal hyperparathyroidism later reverting to FHH has been reported, even in patients with heterozygous CaSR mutations, including the c.554G>A, p.Arg185Gln; R185Q variant present in the family of this report (13, 16–21).