GNRHR and hypogonadotropic hypogonadism: A 17-year-old male patient with isolated hypogonadotropic hypogonadism caused by a GnRH receptor (GNRHR) mutation had no pubertal development and a BA of 14.5 years, and his 16-year-old sister with the same mutation had no thelarche and a BA of 12.5 years (39).