FGF8 and hypogonadotropic hypogonadism: Additionally, genetic causes of isolated hypogonadotropic hypogonadism such as KAL1, FGFR1/FGF8, PROKR2/PROK2, CHD7, or GNRH1 gene mutations [14] have not been studied because the patient had a normal puberty and regular menstruation before the amenorrhea.