Hypocalciuric Hypercalcemia Presenting as Neonatal Rib Fractures

A 2-week-old infant presented with bilateral rib fractures, hypercalcemia, and subperiosteal bone erosions. Parathyroid hormone levels were elevated and urine calcium low. Her parent's laboratory test results were normal. Gene sequencing revealed a new mutation of the calcium-sensing receptor gene, causing severe neonatal hyperparathyroidism, a variant of hypocalciuric hypercalcemia. This is a rare cause of neonatal hyperparathyroidism and nonabusive fractures.