Kallmann syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Kallmann syndrome is a condition characterized by delayed or absent puberty and an impaired sense of smell.

This disorder is a form of hypogonadotropic hypogonadism, which is a condition resulting from a lack of production of certain hormones that direct sexual development. These hormones are normally made in a part of the brain called the hypothalamus. Males born with hypogonadotropic hypogonadism often have an unusually small penis (micropenis) and undescended testes (cryptorchidism). At puberty, most affected individuals do not develop secondary sex characteristics, such as the growth of facial hair and deepening of the voice in males, the start of monthly periods (menstruation) and breast development in females, and a growth spurt in both sexes. Without treatment, most affected men and women are unable to have biological children (infertile).

In Kallmann syndrome, the sense of smell is either diminished (hyposmia) or completely absent (anosmia). This feature distinguishes Kallmann syndrome from most other forms of hypogonadotropic hypogonadism, which do not affect the sense of smell. Many people with Kallmann syndrome are not aware that they are unable to detect odors until the impairment is discovered through testing.

Kallmann syndrome can have a wide variety of additional signs and symptoms. These include a failure of one kidney to develop (unilateral renal agenesis), abnormalities of bones in the fingers or toes, a cleft lip with or without an opening in the roof of the mouth (a cleft palate), abnormal eye movements, hearing loss, and abnormalities of tooth development. Some affected individuals have a feature called bimanual synkinesis, in which the movements of one hand are mirrored by the other hand. Bimanual synkinesis can make it difficult to do tasks that require the hands to move separately, such as playing a musical instrument.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Changes in more than 20 genes have been associated with Kallmann syndrome. Among the most common causes of the condition are mutations in the ANOS1, CHD7, FGF8, FGFR1, PROK2, or PROKR2 gene. In some cases, affected individuals have mutations in more than one of these genes. Additionally, researchers have identified mutations in other genes that may contribute to the development and features of Kallmann syndrome, but are unlikely to cause the disease on their own.

The genes associated with Kallmann syndrome play roles in the development of certain areas of the brain before birth. Although some of their specific functions are unclear, these genes appear to be involved in the formation and movement (migration) of a group of nerve cells that are specialized to process the sense of smell (olfactory neurons). These nerve cells originate in the developing nose and then migrate together to a structure in the front of the brain called the olfactory bulb, which is critical for the perception of odors. Studies suggest that the genes associated with Kallmann syndrome are also involved in the migration of neurons that produce a hormone called gonadotropin-releasing hormone (GnRH). Like olfactory neurons, GnRH-producing neurons migrate from the developing nose to the front of the brain. GnRH controls the production of several hormones that direct sexual development before birth and during puberty. These hormones are important for the normal function of the ovaries in women and testes in men.

Studies suggest that mutations in genes associated with Kallmann syndrome disrupt the migration of olfactory nerve cells and GnRH-producing nerve cells in the developing brain. If olfactory nerve cells do not extend to the olfactory bulb, a person's sense of smell will be impaired or absent. Misplacement of GnRH-producing neurons in the brain prevents the production of other sex hormones, which interferes with normal sexual development and causes the characteristic features of hypogonadotropic hypogonadism. It is unclear how gene mutations lead to the other signs and symptoms that can occur in Kallmann syndrome. Because the features of this condition vary among individuals, additional genetic and environmental factors likely contribute to this disease.

Together, mutations in known genes account for about 30 percent of all cases of Kallmann syndrome. In cases without a mutation in one of the identified genes, the cause of the condition is unknown. Researchers are looking for additional genetic changes that can cause this disorder.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

When Kallmann syndrome is caused by ANOS1 gene mutations, the condition has an X-linked recessive pattern of inheritance. The ANOS1 gene is located on the X chromosome, which is one of the two sex chromosomes. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes), a mutation would have to be present in both copies of the gene to cause the disorder. No females with two ANOS1 gene mutations have been reported in the medical literature. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.

Most of the time, people with Kallmann syndrome resulting from an ANOS1 gene mutation inherit the mutation from their mothers, who carry a single altered copy of the gene in each cell (and generally do not have any signs or symptoms of the condition). Other people have Kallmann syndrome as a result of a new mutation in the ANOS1 gene.

When Kallmann syndrome results from mutations in other genes, it often has an autosomal dominant pattern of inheritance, which means one copy of an altered gene in each cell is sufficient to cause the disorder. In some cases, an affected person inherits the mutation from an affected mother or father. Other cases result from new mutations in the gene and occur in people with no history of the disorder in their family.

In several families, Kallmann syndrome has shown an autosomal recessive pattern of inheritance. Autosomal recessive inheritance means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Kallmann syndrome occurs more often in males than in females, with an estimated prevalence of 1 in 30,000 males and 1 in 120,000 females.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Anosmia · Very frequent (99-80%)

An inability to perceive odors. This is a general term describing inability to smell arising in any part of the process of smelling from absorption of odorants into the nasal mucous overlying the olfactory epithelium, diffusion to the cilia, binding to olfactory receptor sites, generation of action potentials in olfactory neurons, and perception of a smell.

Anterior hypopituitarism · Very frequent (99-80%)

A condition of reduced function of the anterior pituitary gland characterized by decreased secretion of one or more of the pituitary hormones growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, prolactin, luteinizing hormone, and follicle-stimulating hormone.

Decreased testicular size · Very frequent (99-80%)

Reduced volume of the testicle (the male gonad).

Delayed puberty · Very frequent (99-80%)

Passing the age when puberty normally occurs with no physical or hormonal signs of the onset of puberty.

Erectile dysfunction · Very frequent (99-80%)

A multidimensional but common male sexual dysfunction that involves an alteration in any of the components of the erectile response, including organic, relational and psychological.

Hypogonadotropic hypogonadism · Very frequent (99-80%)

Hypogonadotropic hypogonadism is characterized by reduced function of the gonads (testes in males or ovaries in females) and results from the absence of the gonadal stimulating pituitary hormones: follicle stimulating hormone (FSH) and luteinizing hormone (LH).

Hyposmia · Very frequent (99-80%)

A decreased sensitivity to odorants (that is, a decreased ability to perceive odors).

Hypothalamic gonadotropin-releasing hormone (GNRH) deficiency · Very frequent (99-80%)

Gonadotropin-releasing hormone (GnRH) deficiency (IGD) is characterized by inappropriately low serum concentrations of the gonadotropins LH (luteinizing hormone) and FSH (follicle-stimulating hormone) in the presence of low circulating concentrations of sex steroids (primarily testosterone or estradiol). GnRH is not typically assayed directly because it is released in pulses from the hypothalamus, and its concentration can fluctuate rapidly and in a complex pattern that makes single blood measurements less informative than the pituitary's response.

Other findings in the same source

From: Orphanet

Additional reported features include Micropenis (Very frequent (99-80%)); Decreased fertility (Very frequent (99-80%)); Hypoplasia of penis (Very frequent (99-80%)); Breast hypoplasia (Frequent (79-30%)); Cryptorchidism (Frequent (79-30%)); Reduced bone mineral density (Frequent (79-30%)); Abnormality of the voice (Frequent (79-30%)); Abnormal cardiovascular system morphology (Occasional (29-5%)); Abnormal morphology of female internal genitalia (Occasional (29-5%)); Ataxia (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Kallmann syndrome is Endocrinology, with a endocrinologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which hormone or metabolic finding is important in this case?
• How should test timing and current medicines be taken into account?
• What follow-up would show whether the care plan is working?

Treatment discussions and follow-up

Where the source describes treatments, these are an overview of possible care, not a prescription for an individual. Ask which option applies to the confirmed diagnosis, what benefit is expected, what adverse effects to watch for and how progress will be assessed. Availability, approvals and local practice can differ from the country described in the source.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.