Answer is D (Decreased formation of c-AMP is observed) The most common subtype of Pseudohypoparathyroidism (PHP-Ia) is typically associated with reduced / decreased cAMP production in response to exogenous PTH Pseudohypoparathyroidism is associated with decreased formation of cyclic AMP and not decreased cyclic GM P or Inositol Triphosphate The Gs family of G-proteins use the activation of adenylate cyclase as the next step in signal transduction, to produce cyclic AMP Pseudohypoparathyroidism(Ia) is associated with 'loss of function' mutation of Gsa subunit, and hence results in decreased formation of cyclic AMP Pseudohypoparathyroidism is associated with reduced urinary c-AMP response to PTH The term 'Pseudohypoparathyroidism' describes a heterogeneous syndrome characterized by biochemical Hypoparathyroidism (Hypocakemia & Hyperphosphatemia) with paradoxical increased plasma levels of PTH. This is caused by peripheral unresponsiveness to the biological action of PTH or PTH resistance. Although several subtypes of Pseudohypoparathyroidism are identified, the most common subtype of PHP (PHP la) is characterized by deficient urinary cyclic AMP response to administration of exogenous PTH. Failure of cAMP production in these patients after PTH infusion is believed to result from a defect in cyclic AMP mediated signal transduction from a Gsa Loss of function' mutation as depicted in the figure (previous heading) 'The measurement of cyclic AMP in urine following an infusion of synthetic PTH is now used to establish a diagnosis of PTH resistance' - William's Endocrinology 11'"/1243 Pseudohypoparathyroidism is associated with a 'loss of function' inherited G sa mutation. Endocrine diseases can result from either 'loss' or 'gain' of gene function (acquired or inherited) Pseudohypoparathyroidism(la) results from an inherited 'loss of function' mutation of the Gsa subunit Gsa activating mutation (`Gain of function') Gsa inactivating mutation (`Loss of function') * Acromegaly * Pseudohypoparathyroidism(la) * Pituitary coicotroph Adenoma * Mc.Cune Albright syndrome * Hyperfunctioning Thyroid Adenomas * Endocrine ovarian neoplasms Taken from 'Principles & practice of Endocrinology and Metabolism'