The anosmia and sterility of Kallmann's syndrome arise when olfactory axons and gonadotropin-releasing hormone (GnRH) neurons, which are needed for pituitary gonadotropin release, fail to enter the embryonic forebrain (Cadman et al., 2007; Cariboni et al., 2007; Hardelin and Dodé, 2008). This evidence concerns the gene GNRH1 and Kallmann syndrome.