Journal Number 93
November 2005


The Science of Scents - 5: Specific Anosmia and Boronia Nose
By Ian St George

The Column, disappointed in my series on scent because it had little direct reference to NZ orchids, and because it didn't mention his personal inability to smell Boronia (a form of specific anosmia), has spurred me to continue the series. I shall do so by using a number of direct quotes from the net.

Some individuals are completely unable to detect certain odours, a condition known as specific anosmia. An example of this applies to the inability of some doctors to smell ketones, found in the breath of patients with poorly controlled diabetes. This inability is an all-or-nothing phenomenon, with about a quarter of doctors failing to detect this smell. Anosmias such as this are usually genetic in origin.

It is now generally accepted that women are more sensitive to odours than men. This was confirmed by The National Geographic Smell Survey conducted in late 1986. Age of respondents also appears to play a major role in acuity, with definite decreases occurring past age 50. Loss of sensitivity with age is not just restricted to detection threshold levels but also to impairment of the ability to discriminate foods and odours. In addition, screening 764 laboratory employees for one or more of six anosmia types showed 3% to 47% had specific anosmias in various odour categories, with a general anosmia to all odours of 0.2%. 47% of respondents could not smell the "urinous" odour of one compound, 36% could not smell the "malty" odour of isobutyraldehyde, and 12% could not smell the musk Thibetolide or Exaltolide.

A minority of Europeans have specific anosmia for Freesia, although most Europeans report that Freesia is one of the strongest scents known to them. McWhirter concluded that inability to perceive the scent is a recessive character. Tests of 1,600 subjects showed that the frequency of the recessive phenotype was high in those of Eastern European and British Celtic descent (at about 10%) and low in those predominantly of Scandinavian, English, Dutch, and German descent (at about 4%) mpl=dispomimTemplate&list_uids=229250

Most of us probably suffer from specific anosmia. Different species, and even different individuals within a species, appear to have genetic variations in their smell repertoire. Although the androstenone in boar saliva drives sows wild, only half of all humans can smell it at first sniff, according to Monell psychobiologist Charles Wysocki, who keeps a spray bottle of the substance handy. Most of the nonsmellers probably lack the genes that produce the necessary receptors, while some apparently have the right genes but for unknown reasons still don't produce enough working receptors-at least not at first. "About one-quarter of the nonsmellers can be trained to smell it," Wysocki says. "We think exposing the receptor cells to the molecules induces them to function."

At any rate, our personal limitations in smell shouldn't necessarily be regarded as a problem, contends Wysocki. They are simply part of our genetic individuality. He, for one, actually likes the smell of skunk. "I may have an anosmia for some of its offensive compounds, and what remains of the odour is pleasant," says Wysocki. "I roll down the windows of my car to capture it."

Insensitivity to single odours, called specific anosmia, has been repeatedly reported in the literature. The main question of the present study was whether olfactory sensitivity is induceable in subjects with specific anosmia. For this reason the olfactory sensitivity of women with specific anosmia to the volatile steroid androstenone was investigated by threshold measurements twice: before and after repeated odour exposure. Androstenone is a compound that contributes to human body odour and is found at a higher concentration in male axillary sweat than in female sweat. The results show that olfactory perception of androstenone could be induced in more than 80% of the odour-exposed anosmics.

Male inbred mice were tested for relative odorant sensitivity using a conditioned aversion technique and odours classified as primary or complex for humans. Two strains of mice appeared to be less sensitive to the primary odorant isovaleric acid than were seven other inbred mice. The genotype may provide an animal model of a specific anosmia as characterized among humans. Wysocki CJ, Whitney G, Tucker D. Specific anosmia in the laboratory mouse.

Gas chromatography/olfactometry (GC/ O), commonly used to identify odour active chemicals in extracts and headspaces, can present a subject with pure odorants in precise doses. Because of the precision of the dose delivered by GCO and its ability to examine scores of chemicals in a single test it is an ideal tool to study differences in human subjects. Normal olfactory acuity measured as thresholds is usually defined as responses less than two standard deviations from a population mean or the mean of the most sensitive group in a bimodal distribution. Further deviation is then defined as specific anosmia. The objective of this research is to formulate a standard odorant mixture that can be used to test individuals for specific anosmia. Friedrich, J.E. and Acree, T.E. Formulation of a standard odorant mixture to test human sniffers for specific anosmia.

It seems that 12-13% of all people have specific anosmia to the odours that are linked to peatiness in Scotch whisky. This means they either can't smell them, or identify the smell as something totally inappropriate. Tests were done using phenol (the medicinal/TCP characteristic of Islay malts), and Oil of Cade, a wood-smoke condensate which provides smokiness. A lot of Cade-anosmics say they smell mouldy-mustiness, which is actually very different from wood smoke. Perhaps those whisky drinkers who turn up their noses at Islay malts in fact cannot detect the gorgeous phenolics, or think their Islay dram tastes of a mouldy old apron.

The really sad cases are those who can taste peatiness, but don't like it. Perverse, I call them - in fact they are probably the sort of people who enjoy the flavour of nuts. Reference: Burtles, Sheila M. 1990: Fundamental problems encountered when evaluating Scotch whisky by sensory methods. Proceedings of the 3rd Aviemore Conference on Malting, Brewing and Distilling. Institute of Brewing. London: pp 253-265.

Specific anosmia and parasomia are widespread phenomena even amongst perfumiers. There are differences in odour discriminatory abilities between the sexes and the powers of perception fall off with increasing age. ... descriptions of odour are subjective. Hedonistic appraisal, like or dislike, and judgements of intensity of specific odour characters, can be influenced by previous events and other factors.

The Nobel Prize for medicine has just been awarded to Linda Buck and Richard Axel for their work on the sense of smell.




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