Kallmann syndrome is a medical condition marked by the delayed onset or absence of puberty, along with an impaired or absent sense of smell, known as hyposmia or anosmia respectively. It is a type of hypogonadotropic hypogonadism, which involves the deficient production of sex hormones responsible for secondary sexual development and maturation.
This is because of the failure of the hypothalamus to release the corresponding stimulating releasing hormones, or gonadotropins. As the sex hormones and their function differ according to gender, the symptoms of the condition vary accordingly.
The syndrome affects approximately 1 in 10,000 to 86,000 people and is more common in males than females. There are four different types of the conditions and, of these, Kallmann syndrome 1 is the most prevalent.
Signs and Symptoms
The signs and symptoms of Kallmann syndrome are primarily gender-specific as they are related to the reduced function of sex hormones in the body.
Male patients are often born with a particularly small penis, known as micropenis, and undescended testes. At the normal age of puberty, they show reduced growth of facial, pubic and body hair, and continue to have a high-pitched voice that does not deepen. Female patients do not begin menstruating at the normal age of puberty and there is little or no evidence of breast development.
Hyposmia or anosmia is another characteristic symptom that affects both females and males. This diminished sense of smell sets Kallmann syndrome apart from other types of hypogonadotropic hypogonadism conditions. However, the impairment of smell is usually discovered in diagnostic tests because most patients are not aware of their reduced olfactory sensitivity.
Other symptoms may include:
- Cleft lip – only in types 1 and 2
- Cleft palate – in types 1 and 2
- Abnormal eye movements
- Loss of hearing
- Abnormal tooth development
Several gene mutations have been linked to Kallmann syndrome as causative factors. Most of these are involved in various parts of fetal brain development. These include:
- ANOS1 (Kallmann syndrome 1)
- FGFR1 (Kallmann syndrome 2)
- PROKR2 (Kallmann syndrome 3)
- PROK2 (Kallmann syndrome 4)
These genes are also linked to the production of gonadotropin-releasing hormone (GnRH) and other hormones that are needed to initiate puberty and promote sexual function and development.
The standard treatment for Kallmann syndrome is replacing the deficient hormones to induce puberty and normalize the hormone levels. In male patients, this involves testosterone replacement, whereas females require estrogen and progestin therapy to induce secondary sex characteristics at puberty.
Various formulations may be used, including intramuscular injections and topical patches, gels or liquids. The dose usually needs to be tailored to each individual, particularly during certain life stages.
If the patient desires to conceive a child, further treatment may be required to induce fertility. For males, gonadotropin medication to stimulate testicular growth and initiate sperm production is recommended. For females, treatment with gonadotropins of pulsatile GnRH can stimulate folliculogenesis, or the production of mature egg cells. In vitro fertilization may be needed in some cases to allow patients to conceive.
Kallmann syndrome is considered to be a rare condition. One French study found the prevalence of the condition without an identifiable cause was 1 in 10,000 men. Another study involving the Sardinian military reported a lesser prevalence of 1 in 86,000 men. Males are more likely to be affected than females, with a ratio of 4:1. This is because the condition is transmitted in an X-linked recessive manner.
The survival rates with the condition are not lower than the average. In other words, the life expectancy is not expected to change unless the individual is also affected by another condition, such as congenital heart disease or neurological disorders.
Reviewed by Dr Liji Thomas, MD.