The same molecular defects of the gonadotropin-releasing hormone receptor determine a variable degree of hypogonadism in affected kindred

Detailed endocrinological studies were performed in the three affected kind red of a family carrying mutations of the GnRH receptor gene. All three wer e compound heterozygotes carrying on one allele the Arg(262)Gln mutation an d on the other allele two mutations (Gln(106)Arg and Ser(217)Arg). When exp ressed in heterologous cells, both Gln(106)Arg and Ser(217)Arg mutations al tered hormone binding, whereas the Arg(262)Gln mutation altered activation of phospholipase C. The propositus, a 30-yr-old man, displayed complete idiopathic hypogonadotr opic hypogonadism with extremely low plasma levels of gonadotropins, absenc e of pulsatility of endogenous LH and alpha-subunit, absence of response to GnRH and GnRH agonist (triptorelin), and absence of effect of pulsatile ad ministration of GnRH. The two sisters, 24 and 18 yr old, of the propositus displayed, on the cont rary, only partial idiopathic hypogonadotropic hypogonadism. They both had primary amenorrhea, and the younger sister displayed retarded bone maturati on and uterus development, but both sisters had normal breast development. Gonadotropin concentrations were normal or low, but in both cases were rest ored to normal levels by a single injection of GnRH. In the two sisters, th ere were no spontaneous pulses of LH, but pulsatile administration of GnRH provoked a pulsatile secretion of LH in the younger sister. The same mutations of the GnRH receptor gene may thus determine different d egrees of alteration of gonadotropin function in affected kindred of the sa me family.