HS chains are known to function as co-factors and have previously been shown to be part of many signaling pathways (Bülow and Hobert 2006; Bishop et al. 2007), including but not limited to the fibroblast growth factor receptor FGFR, the Slit/Robo ligand/receptor cassette of axon guidance factors, and also the neural cell adhesion molecule KAL1/anosmin-1, which causes hereditary Kallmann syndrome (KS)/idiopathic hypogonadotropic hypogonadism (IHH) (Franco et al. 1991; Legouis et al. 1991). The gene discussed is CHL1; the disease is Kallmann syndrome.