PTH and hyperphosphatemia: Autosomal dominant hypocalcaemia 1 (ADH1, MIM#601198) is characterized by varying degrees of hypocalcemia, a tendency towards hyperphosphatemia, low-to-normal serum parathyroid hormone (PTH) levels and relative hypercalciuria.[1] Most patients with ADH1 are known to have activating mutations of the calcium-sensing receptor gene (CASR, MIM#601199).[2] The protein of calcium-sensing receptor (CASR) is a G protein-coupled cell surface receptor and mainly expressed in parathyroid chief cells, calcitonin-producing thyroid cells, bone cells and renal tubular cells.