[Difference in the therapeutic response to active vitamin D3 between PTH-deficient hypoparathyroidism and...

Pseudohypoparathyroidim (PHP) type I is a disorder characterized by deficient Gsalpha activity at the renal proximal tubules causing resistance to PTH. Physiological calcium reabsorption at the distal tubules depends on an ion channel called TRPV5, expression and function of which is regulated by coordinated actions of PTH and active vitamin D. In PHP patients, it has been demonstrated that, in contrast to proximal tubules, distal tubules do respond to PTH because the GNAS gene coding for Gsalphais not imprinted at the distal tubular cells responsible for calcium reabsorption. Therefore, in order to maintain the same serum calcium levels, urinary calcium excretion as well as the required dosage of active vitamin D is lower in PHP than in PTH-deficient hypoparathyroidism.