[Molecular genetics of Kallmann syndrome: an update]

Kallmann syndrome (KS) is a clinically and genetically heterogeneous disorder that occurs in either an inherited or a sporadic manner. KS results from failed embryonic migration of GnRH-1 neurons from the nasal placode to the hypothalamus, due to the abnormal development of olfactory nerves and bulbs. Hypogonadotropic hypogonadism is related to GnRH deficiency, and anosmia is associated with the absence or hypoplasia of olfactory bulbs and tracts. KS patients can also present some non-reproductive or non-olfactory anomalies in addition to the above typical symptoms. For the high complexity of the molecular genetic mechanism of KS, to date, only 6 KS-related genes have been identified. The KAL1 gene is responsible for the X chromosome-linked recessive form of KS, while the fibroblast growth factor receptor 1 (FGFR1/KAL2) and fibroblast growth factor 8 (FGF8/KAL6) genes are related to the autosomal dominant form of the disease. However, the mutations in these 6 genes account for only about 25 - 30% of all KS cases, which suggests that other pathogenic genes involved in KS remain to be discovered. This article presents an overview on the studies of the pathogenic genes, clinical diagnosis and treatment of KS.