- G proteins can undergo loss-of-function or gain-of-function mutations that cause disease.  In one form of pseudyhypoparathyroidism, a mutated Gs(alpha) fails to respond to parathyroid hormone, producing the symptoms of hypoparathyroidism without any decline in circulating parathyroid hormone.


Reference:
1. Ganong's Review of Medical Physiology: 23rd Edition.  Kim E. Barrett et al.  McGraw-Hill Publishing. 2010.