GNRH1 and Kallmann syndrome: The olfactory defects can occur as a result of the close link between GnRH neurons and olfactory axons; in fact, an embryonal abnormal migration of GnRH neurons and olfactory fibres from their origin in the olfactory placode to the forebrain can result in a hypoplasia or aplasia of the olfactory tract/bulbs associated to GnRH deficiency, that is usually described in CIHH as Kallmann Syndrome (116).