Misrouted cell surface GnRH receptors as a disease aetiology for congenital isolated hypogonadotrophic hypogonadism.

GnRH plays an essential and central role in neuroendocrine control of reproductive function. The GnRH receptor is located on the plasma membrane of gonadotrophs, pituitary cells that synthesize the gonadotrophins LH and FSH. This receptor belongs to the superfamily of G protein-coupled receptors, and is preferentially coupled to the G(q/11) protein; its activation by GnRH analogues stimulates the synthesis and release of LH and FSH. Resistance to GnRH by inactivating (loss-of-function) mutations of the human GnRH receptor leads to distinct forms of sporadic or inherited hypogonadotrophic hypogonadism. Although in vitro expression of a number of these mutated GnRH receptors in heterologous systems has shown that these mutations appear to alter several functions of the molecule, including ligand binding, receptor activation or interaction with coupled effectors, recent observations from our laboratory have challenged this view and indicated that protein misfolding and resultant misrouting is a mechanism that, by itself, may lead to loss of function of the human GnRH receptor. In this review we describe the experimental data that led us to this conclusion and how these studies revealed previously unsuspected features of the mutant human GnRH receptor.