Kallmann syndrome

Kallmann syndrome is a genetic condition where the primary symptom is a failure to start puberty or a failure to fully complete it. It occurs in both males and females and has the additional symptoms of hypogonadism and almost invariably infertility. Kallmann syndrome also features the additional symptom of an altered sense of smell; either completely absent (anosmia) or highly reduced (hyposmia). Kallmann syndrome occurs when the hypothalamic neurons that are responsible for releasing gonadotropin-releasing hormone (GnRH neurons) fail to migrate into the hypothalamus during embryonic development. Kallmann syndrome is a part of a group of conditions that come under the term hypogonadotropic hypogonadism (HH). The sense of smell is only affected in approximately 50% of HH cases and these cases are termed Kallmann syndrome. Apart from the sense of smell there is no difference in the diagnosis or treatment of a case of HH or a case of Kallmann syndrome.The terminology used when describing cases of HH can vary. The term congenital hypogonadotropic hypogonadism (CHH) is now often used. Other terms used include idiopathic / isolated hypogonadotropic hypogonadism (IHH), normosmic hypogonadotropic hypogonadism (nHH) or hypothalamic hypogonadism. The term HH can be used to cover all cases, including Kallmann syndrome. The term isolated GnRH deficiency (IGD) has increasingly been used to describe these group of conditions as it highlights the primary cause of these conditions and to distinguish them from other conditions such as Klinefelter syndrome or Turner syndrome which share some similar symptoms but have a totally different etiology.The term hypogonadism describes a low level of circulating sex hormones; testosterone in males and oestrogen and progesterone in females. Hypogonadism can occur through a number of different methods. The use of the term hypogonadotropic relates to the fact that the hypogonadism found in HH is caused by a disruption in the production of the gonadotropin hormones normally released by the anterior pituitary gland known as luteinising hormone (LH) and follicle stimulating hormone (FSH).LH and FSH have a direct action on the ovaries in women and testes in men. The absence of LH and FSH means that initially puberty will not commence at the correct time and subsequently the ovaries and testes will not perform their normal fertility function with the maturation and release of eggs in woman and the production of sperm in men alongside their role in producing the sex hormones.The underlying cause of the failure in production of LH and FSH is the impairment of the hypothalamus to release the hormone GnRH which in normal circumstances induces the production of LH and FSH. Without the correct release of GnRH the pituitary gland is unable to release LH and FSH which in turn prevents the ovaries and testes from functioning correctly. This failure in GnRH production can either be due to the absence of the GnRH releasing neurones inside the hypothalamus or the inability of the hypothalamus to release GnRH in the correct pulsatile manner to ensure LH and FSH release from the pituitary.HH can occur as an isolated condition with just the LH and FSH production being affected or it can occur in combined pituitary deficiency conditions such as CHARGE syndrome.To date at least twenty five different genes have so far been implicated in causing Kallmann syndrome or other forms of HH through a disruption in the production or activity of GnRH. The 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 very problematic.Kallmann syndrome was described in a paper published in 1944 by Franz Josef Kallmann, a German-American geneticist.The link between anosmia and hypogonadism had already been noted however, in particular by the Spanish doctor Aureliano Maestre de San Juan in 1856.The condition is sometimes known by his name in Spanish speaking countries.The condition has a low prevalence, estimated at 1 in 4,000 for male HH cases overall and 1:50,000 for Kallmann syndrome. It is three to five times more common in males than females. Though whether this is a true gender imbalance or a reflection on how difficult KS / HH is to diagnose correctly in males and females has yet to be fully established.