Pseudohypoparathyroidism

**Definition:** Pseudohypoparathyroidism is a condition with refractoriness to parathyroid hormone of its target tissues especially kidney that causes hypocalcaemia and hyperphosphataemia even in the presence of high circulating levels of biologically active parathyroid hormone.

**Long definition:** Pseudohypoparathyroidism (PHP) is a heterogeneous group of disorders characterized by hypocalcemia, hyperphosphatemia, increased serum concentration of parathyroid hormone (PTH), and insensitivity to the biological activity of PTH. Several variants of PHP have been identified: the molecular defects in the gene (GNAS1) encoding the alpha subunit of the stimulatory G protein (Gsa) contribute to at least 3 different forms of the disease: PHP type 1a, PHP type 1b, and pseudopseudohypoparathyroidism (pseudo-PHP). All patients with severe symptomatic hypocalcemia should be initially treated with intravenous calcium, while oral calcium and 1alpha-hydroxylated vitamin D metabolites, such as calcitriol, remain the mainstay of treatment and should be initiated in every patient with a diagnosis of PHP.