Kallmann syndrome is a rare genetic condition characterized by two main features: a delayed or absent puberty due to low levels of gonadotropin- releasing hormone (GnRH), and a reduced or absent sense of smell (hyposmia or anosmia). Key points

• Cause and mechanism: It results from impaired development or migration of GnRH-producing neurons during embryonic life, leading to congenital hypogonadotropic hypogonadism. The same developmental defect often affects the olfactory system, causing smell impairment.

• Symptoms: In boys, puberty can be late or incomplete, with small testes and little or no increase in secondary sexual characteristics. In girls, delayed puberty is common. Smell disturbance ranges from partial loss to complete loss from birth.

• Genetics: KS is genetically heterogeneous. Many genes involved in GnRH neuron development and olfactory system formation have been implicated, and most cases are sporadic though familial forms exist.

• Related conditions: Normosmic idiopathic hypogonadotropic hypogonadism (nIHH) is a related form where the sense of smell is normal. KS and nIHH are both due to GnRH deficiency, but KS includes olfactory defects.

• Diagnosis: Typically suspected in adolescence due to lack of puberty onset plus smell impairment; confirmed with hormonal testing showing low GnRH/FSH/LH, and imaging or olfactory testing. Genetic testing can identify specific causative mutations.

• Treatment: Management focuses on inducing and maintaining pubertal development and fertility, using hormone replacement therapy (testosterone in males, estrogen/progestin in females) and, if fertility is desired, fertility-inducing regimens with gonadotropins or pulsatile GnRH. Olfactory issues do not usually improve with hormonal therapy.

• Prevalence and impact: KS is uncommon, with estimates in the literature around 1 in 8,000 males and 1 in 40,000 females, though exact figures vary and may be underestimated. The condition can be associated with additional non-reproductive anomalies depending on the genetic form.

If you’d like, I can tailor this to a specific context (e.g., a patient-facing summary, exam prep, or a quick clinical checklist) or pull up the latest patient resources and support networks.