Clinical Presentation and Diagnostic Challenges of Familial Hypocalciuric Hypercalcemia Type 3: A Case Report

We report the case of a male patient in his early thirties presenting with persistent hypercalcemia and a notable family history of hypercalcemia. Both his mother and brother were diagnosed with primary hyperparathyroidism and had undergone parathyroidectomy. Initial biochemical investigations demonstrated elevated serum calcium and parathyroid hormone levels, but low urinary calcium excretion, raising suspicion for familial hypocalciuric hypercalcemia (FHH). Genetic testing subsequently revealed a pathogenic mutation in the AP2S1 gene, confirming FHH type 3. This case highlights the diagnostic challenges in distinguishing FHH from primary hyperparathyroidism and emphasizes the importance of genetic analysis in guiding appropriate management.