Kallmann syndrome, also known as hypogonadotropic hypogonadism with loss of smell, is a congenital genetic disorder. Kallmann’s syndrome was first reported in 1944 in nine men with familial hypogonadism combined with loss of smell or hyposmia. The disease is familial or sporadic and can occur in both sexes, with an incidence of approximately 1/10,000 in men and 1/50,000 in women.1 Pathogenesis During human embryonic development, the olfactory nerve in the nasal cavity transmits the sense of smell to the hypothalamus and other parts of the brain. The olfactory nerve is completed around day 25 of embryonic development. GnRH cells that occur in the nasal cavity travel up the olfactory nerve during embryonic development to the hypothalamus, stopping at the arcuate nucleus of the hypothalamus. There the GnRH neurogen secretes GnRH, which stimulates the pituitary gland to secrete LH and FSH, the latter two stimulating the gonads to produce testosterone (or androgens) and sperm (ova) production. When the olfactory nerve is underdeveloped or does not reach the hypothalamus, the GnRH neurogen does not reach the hypothalamus and thus cannot secrete GnRH at its normal site, thus affecting the physiological function of reproduction. This then explains why reproductive physiology disorders often coexist with olfactory dysfunction in patients with Kalman’s syndrome. The gene associated with this disorder is KALIG-1, which is located on the short arm of the X chromosome. KALIG-1 is a large gene with about 200,000 base pairs, and the occurrence of Kalman’s syndrome is associated with the deletion or mutation of this gene. In contrast, those with normal olfaction used to be called idiopathic hypogonadotropic hypogonadism due to mutations in the gene for gonadotropin-releasing hormone, which is located on the short arm of chromosome 8. The clinical manifestations of hypogonadism are gonadal hypoplasia with loss or hyposmia, small testicular size and absence of spermatozoa in males and, in a few cases, cryptorchidism. Female patients present with primary amenorrhea and infantile internal and external genitalia. Rarely, patients may have cleft lip, cleft palate, cryptorchidism, deafness, color blindness and renal abnormalities. Serum testosterone (T) levels are low in male patients and estradiol (E2) levels are low in female patients. Luteinizing hormone (LH) and follicle stimulating hormone (FSH) were low in both male and female patients. Kallmann syndrome showed good or delayed response to GnRH excitation test. Morphological abnormalities of the olfactory organs are best detected by MRI. Disease treatment The clear diagnosis of the disease is the key to treatment. The purpose of treatment is divided into 4 steps: 1. firstly, to promote the development of secondary sexual characteristics; 2. to have a normal sexual life; 3. to promote sperm production and induce fertility; 4. to maintain a normal quality of life and prevent the occurrence of osteoporosis. At present, androgens are mainly taken to achieve the first purpose. Treating male patients with Kallmann syndrome with human chorionic gonadotropin (hCG) and menopausal gonadotropin (HMG) or with GnRH pumps can promote the development of secondary sexual characteristics, increase testicular volume, promote spermatogenesis, and some patients have given birth. In female patients, HMG can be used to induce ovulation and obtain pregnancy. Maintenance of lifelong quality of life and maintenance of bone mass requires hormone replacement.