Autosomal-dominant hypocalcemia type 1 (ADH1) is a rare genetic form of hypoparathyroidism caused by gain-of-function (GoF) variants in the calcium-sensing receptor (CaSR) encoded by CASR. We examined the prevalence, penetrance, and expressivity of GoF CASR variants in the UK Biobank (UKB; n = 433,793), All of Us (AOU; n = 229,987), and Mass General Brigham Biobank (n = 39,081). This evidence concerns the gene CASR and hypoparathyroidism.