Hyperosmia

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Hyperosmia is an increased olfactory acuity (heightened sense of smell), usually caused by a lower threshold for odor. [1] This perceptual disorder arises when there is an abnormally increased signal at any point between the olfactory receptors and the olfactory cortex. The causes of hyperosmia may be genetic, hormonal, environmental or the result of benzodiazepine withdrawal syndrome.

Contents

Causes

Genetics

A study by Menashe et al. has found that individuals with a single nucleotide polymorphism variant in the OR11H7P pseudogene have a lower receptor activation threshold for isovaleric acid. [2] These individuals are hyperosmic for this single odorant.

Another study by Keller et al. has found that people with the intact human odorant receptor OR7D4 are more sensitive to androstenone and androstadienone and thus find them unpleasant (individuals with the semi-functional OR7D4 have two non-synonymous single nucleotide polymorphisms in the OR7D4 pseudogene, resulting in two amino acid substitutions). [3] There has not yet been extensive research into the genetic background of those with general hyperosmia, rather than for just a single odorant.

Environmental

There has not been extensive research into environmental causes of hyperosmia, but there are some theories of some possible causes.

In a study by Atianjoh et al., it has been found that amphetamines decrease levels of dopamine in the olfactory bulbs of rodents. [4] On this basis, it has been hypothesized that amphetamine use may cause hyperosmia in rodents and humans, but further research is still needed. Anecdotal support for the belief that amphetamines may cause hyperosmia comes from Oliver Sacks's account of a patient (who he later revealed to be himself) with a heightened sense of smell after taking amphetamines. [5]

It has been observed that the inhalation of hydrocarbons can cause hyperosmia, most likely due to the destruction of dopaminergic neurons in the olfactory bulb. [6]

Methotrexate, administered in the treatment of psoriasis, has been known to cause hyperosmia, and may be more likely to do so in patients with a history of migraines. [7] However, this is only an observation and not part of a study; therefore, it is yet to be verified.

Treatment

If the cause(s) is/are environmental, normal olfactory acuity will usually return over time, even if it is left undiagnosed or untreated. [5] [6] Hyperosmic individuals may need to avoid exposure to strong odorants for a period of time if the sensation becomes unbearable. [6] Dopamine antagonists such as butyrophenones or thioridazine hydrochloride were used to treat hyperosmia, but were later discontinued due to undesirable side effects. [6]

See also

Related Research Articles

<span class="mw-page-title-main">Olfactory nerve</span> Cranial nerve I, for smelling

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<span class="mw-page-title-main">Olfactory bulb</span> Neural structure

The olfactory bulb is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OFC) and the hippocampus where it plays a role in emotion, memory and learning. The bulb is divided into two distinct structures: the main olfactory bulb and the accessory olfactory bulb. The main olfactory bulb connects to the amygdala via the piriform cortex of the primary olfactory cortex and directly projects from the main olfactory bulb to specific amygdala areas. The accessory olfactory bulb resides on the dorsal-posterior region of the main olfactory bulb and forms a parallel pathway. Destruction of the olfactory bulb results in ipsilateral anosmia, while irritative lesions of the uncus can result in olfactory and gustatory hallucinations.

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Olfactory receptors (ORs), also known as odorant receptors, are chemoreceptors expressed in the cell membranes of olfactory receptor neurons and are responsible for the detection of odorants which give rise to the sense of smell. Activated olfactory receptors trigger nerve impulses which transmit information about odor to the brain. These receptors are members of the class A rhodopsin-like family of G protein-coupled receptors (GPCRs). The olfactory receptors form a multigene family consisting of around 400 genes in humans and 1400 genes in mice.

<span class="mw-page-title-main">Androstenone</span> Chemical compound

Androstenone (5α-androst-16-en-3-one) is a 16-androstene class steroidal pheromone. It is found in boar's saliva, celery cytoplasm, and truffle fungus. Androstenone was the first mammalian pheromone to be identified. It is found in high concentrations in the saliva of male pigs, and, when inhaled by a female pig that is in heat, results in the female assuming the mating stance. Androstenone is the active ingredient in 'Boarmate', a commercial product made by DuPont sold to pig farmers to test sows for timing of artificial insemination.

Trace amine-associated receptors (TAARs), sometimes referred to as trace amine receptors, are a class of G protein-coupled receptors that were discovered in 2001. TAAR1, the first of six functional human TAARs, has gained considerable interest in academic and proprietary pharmaceutical research due to its role as the endogenous receptor for the trace amines phenethylamine, tyramine, and tryptamine – metabolic derivatives of the amino acids phenylalanine, tyrosine and tryptophan, respectively – ephedrine, as well as the synthetic psychostimulants, amphetamine, methamphetamine and methylenedioxymethamphetamine. In 2004, it was shown that mammalian TAAR1 is also a receptor for thyronamines, decarboxylated and deiodinated relatives of thyroid hormones. TAAR2–TAAR9 function as olfactory receptors for volatile amine odorants in vertebrates.

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Olfactory receptor 51E2 is a protein that in humans is encoded by the OR51E2 gene.

<span class="mw-page-title-main">OR11H6</span> Protein-coding gene in the species Homo sapiens

Olfactory receptor 11H6 is a protein that in humans is encoded by the OR11H6 gene.

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<span class="mw-page-title-main">OR51E1</span> Protein-coding gene in the species Homo sapiens

Olfactory receptor 51E1 is a protein that in humans is encoded by the OR51E1 gene.

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<span class="mw-page-title-main">OR11H4</span> Protein-coding gene in the species Homo sapiens

Olfactory receptor 11H4 is a protein that in humans is encoded by the OR11H4 gene.

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<span class="mw-page-title-main">Sense of smell</span> Sense that detects smells

The sense of smell, or olfaction, is the special sense through which smells are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste.

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Odor molecules are detected by the olfactory receptors in the olfactory epithelium of the nasal cavity. Each receptor type is expressed within a subset of neurons, from which they directly connect to the olfactory bulb in the brain. Olfaction is essential for survival in most vertebrates; however, the degree to which an animal depends on smell is highly varied. Great variation exists in the number of OR genes among vertebrate species, as shown through bioinformatic analyses. This diversity exists by virtue of the wide-ranging environments that they inhabit. For instance, dolphins that are secondarily adapted to an aquatic niche possess a considerably smaller subset of genes than most mammals. OR gene repertoires have also evolved in relation to other senses, as higher primates with well-developed vision systems tend to have a smaller number of OR genes. As such, investigating the evolutionary changes of OR genes can provide useful information on how genomes respond to environmental changes. Differences in smell sensitivity are also dependent on the anatomy of the olfactory apparatus, such as the size of the olfactory bulb and epithelium.

<span class="mw-page-title-main">OR1E3</span> Protein-coding gene in the species Homo sapiens

Olfactory receptor family 1 subfamily E member 3 (gene/pseudogene) is a protein that in humans is encoded by the OR1E3 gene.

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References

  1. ↑ Walker, HK (1990). Clinical Methods: The History, Physical, and Laboratory Examinations. Boston: Butterworths. pp. Ch 59.
  2. ↑ Menashe, I; Abaffy, T; Hasin, Y; Goshen, S; Yahalom, V; Luetje, CW; Lancet, D (2007-10-30). "Genetic elucidation of human hyperosmia to isovaleric acid". PLOS Biology. 5 (11): e284. doi: 10.1371/journal.pbio.0050284 . PMC   2043052 . PMID   17973576.
  3. ↑ Keller, A; Zhuang, H; Chi, Q; Vosshall, LB; Matsunami, H (2007-09-27). "Genetic variation in a human odorant receptor alters odour perception". Nature. 449 (7161): 468–72. Bibcode:2007Natur.449..468K. doi:10.1038/nature06162. PMID   17873857. S2CID   4417235.
  4. ↑ Atianjoh, FE; Ladenheim, B; Krasnova, IN; Cadet, JL (2008-07-28). "Amphetamine causes dopamine depletion and cell death in the mouse olfactory bulb". European Journal of Pharmacology. 589 (1–3): 94–7. doi:10.1016/j.ejphar.2008.05.001. PMC   2536718 . PMID   18544452.
  5. 1 2 Sacks, Oliver (1985). The Man Who Mistook His Wife for a Hat . New York: Simon & Schuster. pp.  156–160. ISBN   978-0-684-85394-9.
  6. 1 2 3 4 Henkin, RI (1990-12-05). "Hyperosmia and depression following exposure to toxic vapors". JAMA: The Journal of the American Medical Association. 264 (21): 2803. doi:10.1001/jama.264.21.2803. PMID   2232068.
  7. ↑ Zargari, O (2006-12-10). "Methotrexate, hyperosmia, and migraine". Dermatology Online Journal. 12 (7): 28. doi:10.5070/D34PT9B52W. PMID   17459314. Abstract.
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