Anyone know how congenital anosmia is inherited?

Question

A friend is looking into sperm donors and one donor states that his mother and maternal aunt have no sense of smell since birth. She is wondering how that would effect her children if she used this donor. What are the odds that one would be born with this disorder and what are the odds that her children would be fine, but could pass it on to their children.
We found the name of the disorder on the internet, but no information about its inheritance. Thanks.

Answer 1

Almost all cases of congential anosmia are caused by Kalmann syndrome. While Kalmann syndrome is not particularly life-threatening, it can certainly be no fun for the person who has it, because it causes a delay in development of puberty and what's called a 'micropenis' in the male. Hormone-replacement therapy can straighten most of this out, however.

But your case doesn't sound like Kalmann. For one thing, Kalmann is X-linked, so we would expect females in the family to display the characteristics LESS than males. The other symptoms of the syndrome, too, are noticable and serious enough that it seems likely that the donor would have mentioned it. (If it is Kalmann, and your donor doesn't have it, then the chances of getting it are zero, fortunately!)

If it's not Kalmann, there are a few other things it could be. If we take the account completely at face value, then maybe it's isolated congenital anosmia - anosmia with no other symptoms whatsoever. There have been only nine verified cases of isolated congenital anosmia, and they were in Iranian families (link 1 below). This gene was found to not be sex-linked, dominant, but not always expressed.

If your sperm donor happens to have the extremely rare isolated congential anosmia, then his mother is likely to have only had one copy of the gene. That give the donor a 50% chance of having it and just not expressing it, and his sperm would have a 25% chance of transmitting it to a child. And, of course, even if the child has it, it gene may not be expressed then, either (carriers seem to show anosmia less than half of the time).

Of course, the most likely situation is really that it's not congenital at all. Accidents happen to children and parents sometimes don't know of it or can't recall. Most patients who lose their sense of smell lose it from injury and disease, and if you go back two or three generations those can be more difficult to diagnose and correct. Unless you are POSITIVE it's congenital, it's probably just a coincidence and not heritable at all.

Hope that helps!

Answer 2

Congenital Anosmia

Answer 3

A temporary loss of smell can be caused by a stuffy nose or infection. In contrast, a permanent loss of smell may be caused by death of olfactory receptor neurons in the nose, or by brain injury in which there is damage to the olfactory nerve or damage to brain areas that process smell (see olfactory system). The lack of the sense of smell at birth, usually due to genetic factors, is referred as congenital anosmia. Anosmia may be an early sign of degenerative brain diseases such as Parkinson's disease and Alzheimer's disease. Another specific cause of permanent loss could be from damage to olfactory receptor neurons due to use of nasal sprays. To avoid loss of smell from nasal sprays, use them for only a short amount of time. Nasal sprays that are used to treat allergy related congestion are the only nasal sprays that are safe to use for extended periods of time. Esthesioneuroblastoma is an exeedingly rare cancerous tumor that originates in or near the olfactory nerve.

Upper respiratory tract infection (e.g., sinusitis or the common cold)
Nasal polyps
Smoking
Head trauma
Dementia with Lewy bodies
Parkinson's Disease
Alzheimer's Disease
Toxins (especially acrylates, methacrylates and cadmium)
Old age
Kallmann syndrome
Esthesioneuroblastomais an exeedingly rare cancerous tumor that originates in or near the olfactory nerve. Symptoms are anosmia (loss of sense of smell) often accompanied by chronic sinusitus.

Answer 4

Genetic factors.