CASR and Hypocalcemia: <h4>Backround</h4>Autosomal dominant hypocalcemia type 1 (ADH1) is a rare form of hypoparathyroidism caused by heterozygous, inherited, or de novo activating mutations in the calcium-sensing receptor gene (CASR).<h4>Case presentation</h4>A 29-year-old man was referred to the outpatient department for poorly controlled hypoparathyroidism with hypocalcemia, hypomagnesemia, mild hypokalemia, excessive hypercalciuria, and a worsening eGFR under conventional therapy.