Pseudohypoparathyroidism is an interesting condition in which there is decreased PTH effectiveness on peripheral tissues due to peripheral tissue resistance. One of the mechanisms for this increase in peripheral tissue resistance may be related to loss of an essential component of the PTH-receptor-adenylate-cyclase complex in the cell membrane (the G-protein or nucleotide regulatory unit). Patients with pseudohypoparathyroidism also have somatic features such as short stature, a sharp fourth metacarpal, and obesity (Fig. 18.14). They show no renal response to exogenous PTH administration, unlike normal individuals or patients with primary hypoparathyroidism, who respond to PTH with increased cyclic AMP excretion and phosphate excretion.
