Section 2 - Understanding Kallmann's SyndromeNext Question

11.What has my absent sense of smell got to do with absent puberty ?

It has everything to do with it. At first glance, the two abnormalities may seem unrelated, but what makes Kallmann's syndrome unique is the relationship between anosmia and absent puberty, a relationship already determined before birth. Let's first look at the development of the olfactory system in the normal human embryo.

A normal sense of smell and GnRH-secreting cells

You may remember from the answer to Question 7 that the normal hypothalamus contains GnRH-secreting cells, but interestingly, these cells do not actually originate there. In fact, GnRH-secreting cells start off in the region of the embryo's brain which later becomes responsible for smell (the "primitive nose"). They then migrate to the hypothalamus when the embryo is 6 to 8 weeks old (Figure 10). As the embryo's brain develops further the olfactory system is formed, which creates a type of GnRH "bridge" across which the GnRH-secreting cells can migrate. The baby is then born with a normal sense of smell.

In other words, GnRH-secreting cells (GnRH being the vital ingredient for normal puberty) can only migrate to the hypothalamus if the olfactory bulbs and tracts develop normally during the embryonic phase of development.

Anosmia and the failed migration of GnRH-secreting cells

It is only in recent years that endocrinologists have begun to understand the link between sex & smell. In Kallmann's syndrome, the olfactory system does not develop normally during the first few weeks of an embryo's life and the GnRH-secreting cells have no means of migrating from the nose to the hypothalamus. Without olfactory bulbs and tracts, there is no sense of smell and with no GnRH-secreting cells in the hypothalamus, normal development during puberty is not possible.

As a person with Kallmann's syndrome, you may have had something called an MRI scan of your head (see answer to Question 18). MRI technology is more effective than X-rays in confirming the absence of the olfactory bulbs and tracts. Interestingly, there will always be some olfactory cells and even GnRH-secreting cells present at the top of your nasal cavity, but your olfactory system will remain incomplete and your anosmia is irreversible. Modern medicine has not yet found a way to encourage the GnRH-secreting cells to migrate and so the natural release of GnRH (and therefore the natural regulation of puberty) is currently impossible. However, specialised medical treatment (described in the answers to Questions 19 & 24) has been available for many years and it can carry out the same functions of natural GnRH; i.e. regulation of puberty, the body's sexual characteristics and fertility.