Introduction

Puberty is a normal part of development that usually occurs somewhere between the ages of 8 and 14. During this period, individuals undergo physical growth, hormonal fluctuations, and emotional changes, including the maturation of sexual traits. However, in some individuals, these changes are delayed or fail to happen altogether. This is the case with Kallmann syndrome (KS), a rare genetic disorder characterised by two main symptoms: the delay or absence of puberty and the absence of the sense of smell, known as anosmia.^1,2

KS affects an estimated 1 in 48000 individuals, and is about four 4 times more likely to affect males than females. Recognising the signs of KS is key for early diagnosis and appropriate treatment. With early intervention, KS can be effectively managed so that long-term complications, such as infertility and osteoporosis, can be minimised and. With proper medical care, individuals with KS can lead healthy and productive lives.²

What is Kallmann syndrome?

KS represents a type of hypogonadotropic hypogonadism (HH), indicating that the male testes or female ovaries generate minimal or no sex hormones. KS arises from a disruption in the production or activity of gonadotropin-releasing hormone (GnRH), which is typically secreted by the hypothalamus in the brain. When GnRH is present, it triggers the release of other hormones by the pituitary gland (luteinising hormone (LH) and follicle-stimulating hormone (FSH)) that are essential for puberty and fertility. In KS, GnRH-producing cells do not migrate properly during early development, leading to a disruption that impairs the release of LH and FSH. 

The same developmental issue with GnRH also affects the olfactory bulbs, which are brain structures found in the brain that are involved in our sense of smell. Consequently, a significant symptom of KS is a diminished or absent sense of smell (anosmia).

While there are several reasons why puberty might be delayed, KS is unique in that it combines hormonal deficiency with anosmia. Other causes of delayed puberty, including other forms of HH, usually do not exhibit these two symptoms simultaneously. It is an essential clue in helping healthcare providers distinguish KS from other conditions.

While KS is a genetically based condition, it can be the result of many different gene mutations. Around 40 different genes have been linked to HH, including KS, which accounts for the differences in symptoms. Nevertheless, in roughly 40% of cases, the exact genetic cause is still unknown.^2,3

Symptoms of Kallmann syndrome

Delayed or absent puberty

Puberty is a critical phase in life that marks the physical transition between childhood and adulthood. It is a developmentally important time marked by the appearance of secondary sexual characteristics (breast development, growth of facial and body hair, voice changes, and more), as well as the attainment of reproductive maturity.

The brain triggers the release of GnRH, which acts on the pituitary gland to produce gonadotropin hormones, LH and FSH. These, in turn, stimulate the gonads (ovaries or testes) to make their own sex hormones (testosterone, oestrogen, and progesterone).¹

In KS, this complex hormonal cascade is disrupted by the reduced or absent production of GnRH. As a result, puberty is either significantly delayed or does not occur at all. Little to no breast development and the absence of menstruation are usually observed in females. In males, symptoms can include little to no facial and body hair, no deepening of the voice, and sometimes undescended testicles and underdeveloped external genitalia.²

The absence or delay in puberty can affect people with KS not only physically, but also psychologically. Adolescence is an emotional time for all teenagers, tweens and teens, but for those with KS, seeing the physical changes in their peers can take a toll on their mental health. These young adolescents often have a poor body image and low self-esteem, which can affect their social and intimate relationships. The discrepancy between their age and physical appearance can also make them targets for teasing or bullying, and many report that it affects their mental health and quality of life.⁴

Anosmia or hyposmia (loss or reduction of smell)

Another defining feature of KS is an impaired sense of smell. While some experience a reduction, or hyposmia, others completely lose that sense, a condition referred to as anosmia. As mentioned previously, this symptom is the result of the inappropriate migration of GnRH neurons during development, affecting the development of the olfactory bulbs, which are responsible for our sense of smell. 

This can often be visualised by magnetic resonance imaging (MRI), which will show the missing or underdeveloped olfactory bulbs and tracts. It is important to note that the degree of loss of smell can vary from person to person.

Anosmia or hyposmia is often overlooked, particularly in children, as it is not a visible symptom and can go unnoticed until a child is older or specifically tested. It is a crucial diagnostic clue to distinguish KS from other causes of delayed puberty.^2,4,5

Reproductive and genital anomalies

Because of the disruption in the production of sexual hormones that are critical for normal sexual development, KS is often accompanied by distinctive reproductive and genital anomalies.

In males, some of these symptoms can include:

• Underdeveloped external genitalia (micropenis) 
• Undescended testicles (cryptorchidism)
• A delay (or absence) in the appearance of secondary sexual characteristics

Females with KS often experience:

• A delay or absence of menstruation
• Reduced or absent breast development
• A delay (or absence) in the appearance of secondary sexual characteristics

Left untreated, KS usually leads to infertility. Early diagnosis and adequate treatment are essential to avoid this outcome.^2,4

Non-reproductive symptoms

KS can cause a broad range of other symptoms that are unrelated to the reproductive system. 

• Birth defects such as cleft lip or palate, or a high-arched palate
• Anomalies in their kidney development, most notably a condition called unilateral renal agenesis or solitary kidney, where only one kidney develops
• Neurological defects such as nystagmus and involuntary mirror movements of the hands (bimanual synkinesis)
• Colour blindness
• Hearing loss
• Cardiac anomalies
• Lack of development of one or more teeth

These highlight the broad impact of this condition on development and how it can impact mental health and quality of life.^2,5

Kallmann syndrome diagnosis

The diagnosis of KS involves a thorough process, including the following:^2,5

• Medical history
• Physical examination
• Laboratory tests (particularly hormone levels)
• Imaging (MRI, ultrasound)
• Olfactory testing
• Genetic testing

Delayed puberty is usually the primary cause for consultation and an essential clue for diagnosis. However, a physical examination can also reveal other clinical signs like:

• Undescended testicles
• Underdeveloped male genitalia
• Underdeveloped breasts

Laboratory tests include:

• The measurement of blood levels of gonadotropins (FSH and LH) would show low levels of these hormones. show low levels
• Sex steroids (testosterone in males, oestradiol in females) would be within show normal limits

Additional tests and imaging can help determine the structure of the hypothalamus, pituitary gland, and olfactory bulbs, which may be underdeveloped or absent in KS. An ultrasound of the kidneys may be used to identify associated renal anomalies like unilateral renal agenesis.⁶

Olfactory testing is an essential part of the KS diagnosis. This is evaluated by history as well as formal diagnostic tests. Genetic testing can identify mutations in several genes linked to the disorder, providing further diagnostic clarity.⁵

Treatment and management

Early diagnosis of KS is key to allow early treatment and avoid the lasting consequences of the disrupted hormonal production. Treatment primarily focuses on hormone replacement therapy. Providing these hormones that are not naturally produced allows the induction and maintenance of secondary sexual characteristics, supports bone health, and establishes fertility. 

Males are usually prescribed testosterone, while females receive oestrogen and, later, progesterone. Early treatment can trigger puberty, promote normal growth, and improve overall quality of life by mitigating KS symptoms. When it comes to fertility, specialised treatments such as gonadotropin injections or pulsatile GnRH therapy can stimulate sperm production in men and ovulation in women, making biological parenthood possible for many.

While reproductive symptoms tend to be treated first, KS patients can also exhibit several non-reproductive symptoms. The care of people with KS usually requires a team of specialists, including endocrinologists, fertility experts, nephrologists (kidney doctors) (nephrologists), and ENTs (ear, nose, and throat specialists). Supportive therapies with mental health professionals are also an important part of KS care to help patients cope with the psychological and social challenges.⁷

Summary

KS is a rare genetic condition marked by delayed or absent puberty and a reduced or absent sense of smell (anosmia), due to the abnormal development of a hormonal pathway in the brain, early in life. Symptoms include reproductive and non-reproductive anomalies such as underdeveloped genitalia, hearing loss, or kidney abnormalities. To make a diagnosis, a healthcare provider will usually perform a variety of tests, including measurements of hormone levels in the blood, imaging studies, and genetic evaluation. While patients are often concerned about their fertility, current treatments, such as hormone therapy and fertility-inducing medications, have been successful in achieving fertility for KS patients. While KS can be a scary condition, early diagnosis, coordinated care, and emotional support have allowed people living with KS to lead fulfilling lives with improved health, confidence, and quality of life.