Kallmann syndrome

Kallmann syndrome is an example of hypogonadism (decreased functioning of the sex hormone-producing glands) caused by a deficiency of gonadotropin-releasing hormone (GnRH), which is created by the hypothalamus. Kallmann syndrome is also known as hypothalamic hypogonadism, familial hypogonadism with anosmia, or gonadotropic hypogonadism, reflecting its disease mechanism. more...

Kallman syndrome was described in 1944 by Franz Josef Kallmann, a German geneticist. However, others had noticed a correlation between anosmia and hypogonadism before this such as the Spanish doctor Aureliano Maestre de San Juan 80 years previously.

Features

Kallmann syndrome is characterized by:

• Hypogonadotropic hypogonadism (a lack of the pituitary hormones LH and FSH)
• Congenital (present from birth) anosmia (complete inability to smell) or hyposmia (decreased ability to smell).

It can also be associated with optic problems, such as color blindness or optic atrophy, nerve deafness, cleft palate, cryptorchidism, renal agenesis, and mirror movement disorder. However, it is not clear at this time how or if these other problems have the same cause as the hypogonadism and anosmia and these other problems are more often present in those without Kallmann syndrome.

Males present with delayed puberty and may have micropenis (although congenital micropenis is not present in the majority of male KS cases).

Females present with delayed puberty i.e.primary amenorrhea and lack of secondary sex characteristicd, such as breast development.

Diagnosis

The diagnosis is often one of exclusion found during the workup of delayed puberty. The presence of anosmia together with micropenis in boys should suggest Kallmann syndrome (although micropenis alone may have other causes).

Pathophysiology

Under normal conditions, GnRH travels to the pituitary gland via the tuberoinfundibular pathway, where it triggers production of gonadotropins (LH and FSH). When GnRH is low, the pituitary does not create the normal amount of gonadotropins. The gonadotropins in turn affect the production of hormones in the gonads, so when they are low, the hormones will be low as well.

In Kallmann syndrome, the GnRH neurons do not migrate properly from the olfactory placode to the hypothalamus during development. The olfactory bulbs also fail to form or have hypoplasia, leading to anosmia or hyposmia.

Kallman syndrome can be inherited as an X-linked recessive trait, in which case there is a defect in the KAL gene, which maps to chromosome Xp22.3. KAL encodes a neural cell adhesion molecule, anosmin-1. Anosmin-1 is normally expressed in the brain, facial mesenchyme, mesonephros and metanephros. It is required to promote migration of GnRH neurons from the hypothalamus to the pituitary gland. It also allows migration of olfactory neurons from the olfactory bulbs to the hypothalamus.

Treatment

Treatment is directed at restoring the deficient hormones -- known as hormone replacement therapy (HRT). Males are administered human chorionic gonadotropin (hCG) or testosterone. Females are treated with oestrogen and progestins.

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