- Testotoxicosis is an interesting disease that combines gain and loss of function.  In this condition, an activating mutation of Gs(alpha) causes excess testosterone secretion and prepubertal sexual maturation.  However, this mutation is temperature-sensitive and is active only at the relatively low temperature of the testes (33*C).  At 37*C, the normal temperature of the rest of the body, it is replaced by loss of function, with the production of hypoparathyroidism and decreased responsiveness to TSH.


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