Kallmann syndrome is an endocrine disorder caused by a decrease in sex hormones, either testosterone in males or estrogen and progesterone in females. That decrease leads to a failure to start or complete puberty.
The syndrome is named after Dr. Franz Kallmann, the geneticist who first described it.
Normally, during fetal development there’s a region of the brain called the olfactory placode. Two groups of neurons emerge from that region.
The first group contains olfactory neurons that eventually help with sensing smells.
These neurons migrate down from the olfactory placode and get embedded in the cribriform plate, which is a bone plate that separates the nasal cavity from the brain, forming the olfactory bulb.
The second group contains neurons that release gonadotropin-releasing hormone.
And these neurons migrate through the cribriform plate, and settle in the hypothalamus.
The hypothalamic-pituitary-gonadal axis is a system of hormone signaling between the hypothalamus, pituitary gland, and gonads, either the testes or ovaries, to control sexual development and reproduction.
Gonadotropin-releasing hormone is released into the hypophyseal portal system, which is a network of capillaries connecting the hypothalamus to the hypophysis, or pituitary.
When gonadotropin-releasing hormone reaches the pituitary gland, it stimulates cells in the anterior pituitary, called gonadotrophs, to release gonadotropin hormones, luteinizing hormone and follicle-stimulating hormone into the blood.