Familial hypocalciuric hypercalcemia in an infant: diagnosis and management quandaries.

The article focuses on the diagnosis and management challenges of familial hypocalciuric hypercalcemia type 3 (FHH3) in an infant presenting with hypercalcemia, elevated parathyroid hormone (PTH), hypophosphatemia, and prenatal femoral fractures. FHH3 is a rare autosomal dominant disorder caused by variants in the AP2S1 gene, affecting calcium sensing and typically resulting in higher serum calcium levels than other FHH subtypes. The case describes successful treatment using a combination of a low-calcium formula and cinacalcet, an allosteric modulator of the calcium-sensing receptor, which improved biochemical parameters and maintained clinical stability until the patient was weaned off medication at age four. The report highlights the complexity added by the infant's maternal idiopathic hypoparathyroidism and underscores the need for accurate genetic diagnosis to guide therapy, as well as the limited existing guidelines for managing infantile hypercalcemia in FHH3.