PTH and autosomal dominant hypocalcemia 1: The causes of low PTH in the absence of parathyroid gland structural defects include activating mutations in the calcium-sensing receptor (CASR) leading to suppression of PTH secretion (autosomal dominant hypocalcemia type 1; OMIM 601 198) (7, 8) or in the alpha subunit of the G11 protein (GNA11, autosomal dominant hypocalcemia type 2; OMIM 615 361) (9, 10) which mediates the intracellular signaling of PTH action.