A novel case of neonatal severe hyperparathyroidism successfully treated with a type II calcimimetic drug.

We report a boy with hypercalcemia due to neonatal severe hyperparathyroidism (NSHPT) caused by a compound heterozygous mutation in the calcium sensing receptor (CaSR) managed successfully on a type II calcimimetic drug. The hypercalcemia was temporarily treated by hyperhydration, bisphosphonate and calcium depleted milk. At 29 days of age cinacalcet was introduced. The starting dose was 0.5 mg/kg/day and was subsequently titrated to the point of efficacy (5.2 mg/kg/day) when a persuasive reduction in parathyroid hormone and calcium concentrations was observed. We propose a trial of type II calcimimetics in newborns with NSHPT irrespective of the genetic mutation and advocate that residual functionality of the CaSR predict the drug efficacy.