Kallmann (KAL1) syndrome is an X-linked condition characterized by hypogonadism due to gonadotropin-releasing hormone (GnRH) deficiency, and a defective sense of smell, known as anosmia, due to the underdevelopment of the olfactory bulbs. GnRH is a key regulator of reproduction and sexual behavior. Anosmia associated with Kallmann syndrome is due to a defect in the migration and targeting of GnRH-secreting neurons and olfactory axons during embryonic development. Mutations in the KAL1 gene are responsible for X-linked Kallmann syndrome. The human KAL1 gene, located in the Xp22.3 region, encodes a 680 amino acid extracellular matrix adhesion protein, known as anosmin-1. Anosmin-1 plays an essential role in the patterning of mitral and tufted cell axon collaterals to the olfactory cortex. Anosmin-1 can be detected in the basement membranes and/or interstitial matrices of various structures including bronchial tubes, muscular walls of the digestive tract and forebrain subregions.