Kallmann syndrome (KS) is a clinically and genetically heterogeneous disorder characterized mainly by the co-occurrence of idiopathic hypogonadotropic hypogonadism (IHH) due to the defective action of hypothalamic gonadotropin releasing hormone (GnRH) through the hypothalamic-pituitary-gonadal axis, and anosmia associated with dys/agenesis of the olfactory bulbs. This evidence concerns the gene GNRH1 and Kallmann syndrome.