page_title: Kallmann syndrome
section_title: Genetics
hierarchical_section_title: Kallmann syndrome / Genetics
caption_attribution_description: English: Genes involved in migration or activation of GnRH releasing neurones into the hypothalamus
context_page_description: Kallmann syndrome is a genetic disorder that prevents a person from starting or fully completing puberty. Kallmann syndrome is a form of a group of conditions termed hypogonadotropic hypogonadism. To distinguish it from other forms of hypogonadotropic hypogonadism, Kallmann syndrome has the additional symptom of a total lack of sense of smell or a reduced sense of smell. If left untreated, people will have poorly defined secondary sexual characteristics, show signs of hypogonadism, almost invariably are infertile and are at increased risk of developing osteoporosis. A range of other physical symptoms affecting the face, hands and skeletal system can also occur.
  The underlying cause is a failure in the correct production or activity of gonadotropin-releasing hormone by the hypothalamus. This results in low levels of the sex hormones testosterone in males or oestrogen and progesterone in females. Diagnosis normally occurs during teenage years when puberty fails to start.
  Lifelong treatment for all sexes is normally required. Hormone replacement therapy is the major form of treatment with the aim to replace the missing testosterone or oestrogen and progesterone.
context_section_description: To date at least 25 different genes have been implicated in causing Kallmann syndrome or other forms of hypogonadotropic hypogonadism through a disruption in the production or activity of GnRH (37). These genes involved cover all forms of inheritance and no one gene defect has been shown to be common to all cases which makes genetic testing and inheritance prediction difficult.
  The number of genes known to cause cases of KS/CHH is still increasing. In addition it is thought that some cases of KS/CHH are caused by two separate gene defects occurring at the same time.
  Individual gene defects can be associated with specific symptoms which can help in identifying which genes to test for. Between 35-45% of cases of KS/CHH have an unknown genetic cause.
  The ANOS1 gene defect (previously known as KAL-1) was the first one discovered and the one most commonly tested for. It causes the x-linked form of Kallmann syndrome and is associated with the additional symptoms of anosmia, bimanual synkinesis and renal agenesis. This defect is thought to be responsible for between 5 and 10% of all Kallmann syndrome/CHH cases.
caption: The genetic and molecular basis of idiopathic hypogonadotropic hypogonadism
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