KALLMANN Syndrome

Kallmann syndrome combines an impaired sense of smell with a hormonal disorder that delays or prevents puberty.

The hormonal disorder is due to underdevelopment of specific neurons, or nerves, in the brain that signal the hypothalamus. Without these neurons, the hypothalamus cannot properly stimulate the production and release of certain hormones by the pituitary gland. In normal development, the hypothalamus secretes bursts of gonadotropin-releasing hormone (GnRH) at puberty. These bursts of GnRH trigger the pituitary gland to produce hormones that in turn prompt the release of male and female sex hormones by the gonads (testicles and ovaries) and the development of sperm and egg cells. In Kallmann syndrome, the hypothalamus fails to secrete these bursts of GnRH in utero, during infancy, and at puberty.

The early development of the hypothalamus and sense of smell in the human embryo are both affected in Kallmann syndrome. The portion of the hypothalamus that produces GnRH originally forms as part of the nose and migrates during the early stages of embryonic development to join the rest of the hypothalamus. In Kallmann syndrome, both this portion of the hypothalamus and the smell-detecting (olfactory) neurons in the brain do not develop fully.

When a person has the hormone deficiency characteristic of Kallmann syndrome but has a normal sense of smell, the condition is known as normosmic idiopathic hypogonadotropic hypogonadism (nIHH).

The main symptom of Kallmann syndrome or nIHH is delayed or incomplete puberty. In Kallmann syndrome, this is paired with an impaired sense of smell, a condition present from birth but often not brought to a doctor’s attention until asked about it in the course of diagnosing the cause of delayed puberty.

Other characteristics may also be present in children and adolescents with Kallmann syndrome or nIHH. These can include:

Undescended, or partially descended, testicles

Small penile size

Facial defects, such as cleft lip or palate

Short fingers or toes, especially the fourth finger

Development of only one kidney

Hearing loss

Color blindness

Abnormal eye movements

Abnormal development of the teeth

Mirror hand movements (bimanual synkinesis), in which the movements of one hand are mirrored by the movements of the other

Kallmann syndrome and nIHH are genetic conditions. They are caused by mutations in any of several different genes. Some, but not all, of these have been identified and the inheritance patterns mapped.

Different gene mutations causing Kallmann syndrome and nIHH have different inheritance patterns.

Some must be inherited from both parents (autosomal recessive inheritance). In these types, both parents may be carriers, which means they have no symptoms of the disease.

Others can be inherited from either the mother or the father (autosomal dominant inheritance).

In other types, females are carriers and males have (express) the condition (X-linked inheritance). In these types, the condition can be passed from mothers to sons but not from fathers to sons. Either parent can pass the condition to a daughter as a carrier.

Researchers have more recently identified a fourth inheritance pattern in which mutations in more than one gene may combine to cause the condition (oligogenic inheritance).

Researchers are working to identify all of the genetic mutations associated with Kallmann syndrome and nIHH.

 mutations in any of several different genes. Some, but not all, of these have been identified and the inheritance patterns mapped. Different gene mutations causing Kallmann syndrome and nIHH have different inheritance patterns.

If your child hasn’t started showing signs of puberty around the same time as their peers, then it’s a good idea to schedule a visit with their healthcare provider. They can run the appropriate tests and talk with you about treatment options.

If you’re an adult with Kallmann syndrome and you want to explore fertility options, schedule a visit with your healthcare provider. They can prescribe medications to help you or your partner conceive.

Kallmann syndrome is not a life-threatening disease. However, if left untreated, the condition leads to infertility in both males and females.

There's currently no known cure for Kallmann syndrome. However, continued research is being performed in this area.

In some cases, males with Kallmann syndrome experience a reversal of the condition. This is marked by fertility in the absence of treatment or an improvement in testosterone secretion even after discontinuing testosterone replacement. When this happens, it’s called reversible KS — a condition that has, to date, only been reported in males.