Introduction – brief overview, HRT importance, article purpose

Kallmann Syndrome (KS) is a form of hypogonadotropic hypogonadism - a group of genetic disorders caused by dysfunction in the hypothalamus or pituitary glands affecting the HPG axis.¹ Caused by decreased GnRH secretion, Kallmann Syndrome is characterised by absent puberty and secondary sexual characteristics, as well as anosmia. In both males and females, GnRH (gonadotropin-releasing hormone) is the hormone released from the hypothalamus that stimulates the release of hormones FSH and LH from the anterior pituitary gland.¹ These hormones go on to stimulate the release of the sex hormones - oestrogen in females, and testosterone in males. This process is necessary for puberty and sexual maturity. These hormones cause things such as breast tissue growth, menses, penile growth, facial hair and voice deepening.² The sex hormones also play an important role in determining adult height by stimulating and stopping growth spurts. Individuals with KS will not experience puberty and usually have infertility problems later in life. Other symptoms include increased height and anosmia.

Hormone replacement therapy is the main treatment of KS, thought to work by inducing puberty and sexual maturity, allowing affected individuals to lead somewhat normal lives. Not only does it help with the physical symptoms, but it can also be beneficial in increasing their self-esteem.

Throughout this article, the aim is to explore how hormonal therapy works as a treatment option for KS using testosterone and oestrogen therapy options.

Understanding kallmann syndrome – genetics, symptoms/diagnosis, overall health effect, prevalence + gender

The main symptoms characterising Kallmann Syndrome are a lack of, or reduced sense of smell, as well as developmental symptoms such as no puberty and low muscle mass. These sexual development symptoms are commonly referred to as congenital hypogonadotropic hypogonadism (CHH).

These symptoms arise during early brain development due to defects in genes involved in the development and migration of GnRH³. GnRH’s (gonadotropin-releasing hormone) movement from the olfactory placode to the hypothalamus is necessary to start sexual development, and is controlled by various types of genes. Some of the most commonly associated genes are the KAL1/ANOS1 and FGFR1 genes.⁴ KAL1 is essential for encoding the anosmin-1 gene, which is used in the migration of GnRH from the olfactory placode to the hypothalamus. Without it, the problems previously mentioned can occur. Along with GnRH, olfactory neurons also start in the placode and require transport proteins to move to the hypothalamus. The FGFR1 gene is thought to be involved in transporting both GnRH and olfactory neurons,⁵ explaining why a lack of smell is one of the defining symptoms of Kallmann Syndrome. FGFR1 is encoded by the KAL2 gene.  If these genes have mutated, it will cause both congenital hypogonadotropic hypogonadism (CHH) and problems with smell, as the affected genes also affect olfactory neurons.

Although the majority of KS cases come about due to sporadic mutation (STAT AND REF), it has also been found to result from familial inheritance, with KAL1 mutated cases being X-linked recessive patterns, and KAL2 being autosomal-dominant.⁶

Goals of hormone replacement therapy in KS

There is no set cure for many hypogonadotropic hypogonadisms. Instead of focusing on fixing phenotypes, treatments aim to help you live a more comfortable life. The goal of HRT as a treatment is to induce secondary sexual characteristics and to increase fertility in individuals. This treatment is usually suggested to adolescents and adults, as the main goal at this point would be to stimulate normal sexual development. If an infant is diagnosed with KS, the likely option is surgery (REF). After this, the treatment will need to be taken for life, to maintain consistent results, wellbeing, bone mass and muscle mass in men. 

Testosterone therapy in males with KS

Types of testosterone therapy

How a treatment is administered greatly affects how the drug works on the body, including how fast it works, the strength of the treatment etc.⁷

• Injections (e.g. enanthate, cypionate)
• Transdermal patches and gels
• Oral formulations
• Long-acting formulations (e.g., testosterone undecanoate)

Injections and transdermal patches are the most common forms of administration for testosterone. Patches and gels allow for a stable concentration of testosterone to be administered. It should be remembered that these gels are not meant to be placed on the scrotum REF. Injections allow the hormone to bypass the liver's first-pass metabolism.⁷

Injections of testosterone, hCG, or GnRH can be given to patients. Treatment with these hormones can lead to spermatogenesis. Testosterone treatment is mainly used for penile growth, whereas treatment with hCG (and FSH) is used to induce puberty and its secondary developments.⁷

Treatment initiation and monitoring

• Gradual dose escalation to mimic puberty
• Regular monitoring of testosterone levels, hematocrit, and PSA (in adults)
• Side effects (acne, mood changes, erythrocytosis, sleep apnea)

Estrogen therapy in kallmann syndrome (for females)

Purpose

The purpose of HRT in females is similar to that in males. To start or increase the development of secondary sexual characteristics, to support bone health, and to kick-start menstruation, during puberty or after. 

Forms of estrogen therapy

Estrogen can be administered using various methods, for different objectives and ages. Here are the most common:

• Oral estrogen (e.g., estradiol)
• Transdermal estrogen (patch or gel)
• Conjugated estrogens

Transdermal estradiol therapy is given to girls as young as 10 years old, in hopes of starting puberty with menstruation. The doses start low, around 0.05-0.07μg/kg every night (0.1mg/day if oral).⁸ This dosage mimics natural estradiol levels during gonadarche.⁹ Gonadarche is responsible for gonad growth during early puberty. It is signalled, in girls, by the first period. In older girls, the starting dose is higher and continually increases for 12-24 months after the initial treatment. It can start anywhere from 0.08 to 0.12 μg/kg. This higher dosage prioritises breast development for older girls who have passed the puberty starting age. In adult women, estradiol is given at a dosage of 1-2mg orally, and 50μg transdermally. 

Conjugated estrogens are mixtures of various estrogen forms, derived from pregnant mare urine or synthetic generation. They are less common due to the associated risk. Risks range from numbness to increased mammographic density, which can go on to cause breast cancer.¹⁰

To prevent endometrial hyperplasia, progesterone is added to the treatment alongside estrogen. 

Addition of progesterone

Needed after the first year of estrogen therapy or once breakthrough bleeding starts. Prevents endometrial hyperplasia. Cyclic or continuous regimens.

Monitoring and side effects

Gradual titration to mimic natural puberty. Monitoring hormone levels and response. Side effects (breast tenderness, mood swings, breakthrough bleeding).

Fertility considerations

Infertility in Kallmann Syndrome is one of the treatable causes of infertility in both men and women. Hormone replacement therapy, however, is not the way to do it. Fertility can be induced by pulsatile GnRH or with gonadotropin injections. 

HRT does not restore fertility. Gonadotropin therapy or pulsatile GnRH may be used for fertility induction. Differences in approach between males and females.

Psychosocial and long-term health aspects

Addressing emotional and psychological support. Body image, relationships, and sexual identity. Importance of long-term follow-up (bone health, cardiovascular health).

Conclusion

• Summary of therapy goals and options
• Importance of individualised treatment plans.
• Encouragement for early diagnosis and lifelong care