Though most cases of this disorder have an unknown origin, there is evidence that FGFR-1 (fibroblast growth factor receptor 1) and KAL1 gene defects can lead to Kallman Syndrome. These genes help normal migration of GnRH neurons into the hypothalamus.
This syndrome occurs from defective migration of GnRH releasing neurons to the hypothalamus. This leads to decreased synthesis and release of GnRH in the hypothalamus, leading to decreased gonadotropin release.
Due to low serum testosterone and gonadotropins, LH and FSH, patients can show delayed puberty. This can also manifest as incomplete puberty, which is also a cause of hypogonadotropic hypogonadism.
Anosmia occurs because normal GnRH neurons originate in the olfacory placode, pass through the olfactory bulb to the hypothalamus. If there is a neuron migration issue, where this path is no longer taken, the patient's smell becomes defective because of olfactory bulb development issues.
Due to improper migration of GnRH releasing cells, hypogonadism occurs. Patients have low levels of FSH, LH and resultingly, testosterone and estrogen.
Due to hormone abnormalities, adult patients are often infertile. Males can show low sperm counts, while many females will present with amenorrhea.
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