The differential diagnosis for hypercalcaemia in infancy and childhood includes: parathyroid hormone (PTH)-dependent anomalies, including MEN syndromes I and II and Jansen’s metaphyseal chondrodysplasia; calcium-sensing receptor disorders such as with severe neonatal hyperparathyroidism or familial hypocalciuric hypercalcaemia (a rare genetic disorder); vitamin D-related anomalies including vitamin D intoxication, Williams syndrome, and granulomatous diseases; and disorders related to vitamin A intoxication or immobilization (Figure 1) [1]. The gene discussed is PTH; the disease is neonatal severe primary hyperparathyroidism.