Antti Knaapila

Genetics of Taste and Smell: Poisons and Pleasures

Eating is dangerous. While food contains nutrients and calories that animals need to produce heat and energy, it may also contain harmful parasites, bacteria, or chemicals. To guide food selection, the senses of taste and smell have evolved to alert us to the bitter taste of poisons and the sour taste and off-putting smell of spoiled foods. These sensory systems help people and animals to eat defensively, and they provide the brake that helps them avoid ingesting foods that are harmful. But choices about which foods to eat are motivated by more than avoiding the bad; they are also motivated by seeking the good, such as fat and sugar. However, just as not everyone is equally capable of sensing toxins in food, not everyone is equally enthusiastic about consuming high-fat, high-sugar foods. Genetic studies in humans and experimental animals strongly suggest that the liking of sugar and fat is influenced by genotype; likewise, the abilities to detect bitterness and the malodors of rotting food are highly variable among individuals. Understanding the exact genes and genetic differences that affect food intake may provide important clues in obesity treatment by allowing caregivers to tailor dietary recommendations to the chemosensory landscape of each person.

Food neophobia shows heritable variation in humans.

Food neophobia refers to reluctance to eat unfamiliar foods. We determined the heritability of food neophobia in a family and a twin sample. The family sample consisted of 28 Finnish families (105 females, 50 males, aged 18-78 years, mean age 49 years) and the twin sample of 468 British female twin pairs (211 monozygous and 257 dizygous pairs, aged 17-82 years, mean age 55 years). Food neophobia was measured using the ten-item Food Neophobia Scale (FNS) questionnaire, and its internationally validated six-item modification. The heritability estimate for food neophobia was 69 and 66% in Finnish families (h(2)) and 67 and 66% in British female twins (a(2)+d(2)) using the ten- and six-item versions of the FNS, respectively. The results from both populations suggest that about two thirds of variation in food neophobia is genetically determined.

Genetic Analysis of Chemosensory Traits in Human Twins

We explored genetic influences on the perception of taste and smell stimuli. Adult twins rated the chemosensory aspects of water, sucrose, sodium chloride, citric acid, ethanol, quinine hydrochloride, phenylthiocarbamide (PTC), potassium chloride, calcium chloride, cinnamon, androstenone, Galaxolide™, cilantro, and basil. For most traits, individual differences were stable over time and some traits were heritable (h(2) from 0.41 to 0.71). Subjects were genotyped for 44 single nucleotide polymorphisms within and near genes related to taste and smell. The results of these association analyses confirmed previous genotype-phenotype results for PTC, quinine, and androstenone. New associations were detected for ratings of basil and a bitter taste receptor gene, TAS2R60, and between cilantro and variants in three genes (TRPA1, GNAT3, and TAS2R50). The flavor of ethanol was related to variation within an olfactory receptor gene (OR7D4) and a gene encoding a subunit of the epithelial sodium channel (SCNN1D). Our study demonstrates that person-to-person differences in the taste and smell perception of simple foods and drinks are partially accounted for by genetic variation within chemosensory pathways.

Self-Ratings of Olfactory Function Reflect Odor Annoyance Rather than Olfactory Acuity

Objective/Hypothesis: Self‐ratings of olfactory function often correlates poorly with results of objective smell tests. We explored these ratings relative to self‐rating of odor annoyance, to odor identification ability, and to mean perceived intensity of odors, and estimated relative genetic and environmental contributions to these traits.

Genetic component of identification, intensity and pleasantness of odours: a Finnish family study

Although potential odorant receptor genes have been identified, the precise genetic component of perception of odours is still obscure. Although there is some evidence for heritability of a few olfactory-related traits, no genome-wide search for loci harboring underlying genes has been published to date. We performed a genome-wide scan to identify loci affecting the identification, intensity and pleasantness of 12 odours (cinnamon, turpentine, lemon, smoke, chocolate, rose, paint thinner, banana, pineapple, gasoline, soap, onion) using 146 Finnish adults from 26 families. Several of these traits showed heritable variation in the families. Suggestive evidence of linkage was found for the pleasantness of cinnamon odour (h2=61%) on chromosome 4q32.3 (multipoint logarithm of the odds (LOD) score 3.01), as well as for the perceived intensity of paint thinner odour (h2=31%) on chromosome 2p14 (multipoint LOD score 2.55). As these loci do not contain any known human odorant receptor genes, they may rather harbor genes that affect the central processing than the peripheral detection of the odour signal. Thus, perception of odours is potentially modified by genes other than those encoding odorant receptors.

A Genome-Wide Study on the Perception of the Odorants Androstenone and Galaxolide

Twin pairs and their siblings rated the intensity of the odorants amyl acetate, androstenone, eugenol, Galaxolide, mercaptans, and rose (N = 1573). Heritability was established for ratings of androstenone (h (2) = 0.30) and Galaxolide (h(2) = 0.34) but not for the other odorants. Genome-wide association analysis using 2.3 million single nucleotide polymorphisms indicated that the most significant association was between androstenone and a region without known olfactory receptor genes (rs10966900, P = 1.2 × 10(-7)). A previously reported association between the olfactory receptor OR7D4 and the androstenone was not detected until we specifically typed this gene (P = 1.1 × 10(-4)). We also tested these 2 associations in a second independent sample of subjects and replicated the results either fully (OR7D4, P = 0.00002) or partially (rs10966900, P = 0.010; N = 266). These findings suggest that 1) the perceived intensity of some but not all odorants is a heritable trait, 2) use of a current genome-wide marker panel did not detect a known olfactory genotype-phenotype association, and 3) person-to-person differences in androstenone perception are influenced by OR7D4 genotype and perhaps by variants of other genes.

Experiences of environmental odors among self-reported hyperosmics: a pilot study.

We investigated everyday odor experiences in 55 people (14–75 years old) who rated their sense of smell as far better than average. Compared to 55 gender- and age-matched controls, the self-reported hyperosmics scored higher on the Affective Impact of Odor Scale, rated negative consequences and unpleasant memories due to odors as more likely, rated environmental odors as more annoying, reported increased sensitivity to specific odors more frequently, paid more attention to odors, and agreed more strongly that their sense of smell has caused inconvenience to them. Based on these data, subjective hyperosmia is associated with primarily negative odor-related experiences.

Fuzzy liquid analysis by an array of nonspecifically interacting reagents: the taste of fluorescence.

Complex or unknown liquid analysis requires extensive instrumentation and laboratory work; simple field devices usually have serious limitations in functionality, sensitivity, and applicability. This communication presents a novel, effective, and simple approach to fingerprinting liquids. The method is based on nonspecific interactions of the sample liquid, a long lifetime luminescent europium label, and various surface modulators in an array form that is readily converted to a field analysis μTAS system. As compared to existing e-nose or e-tongue techniques, the method is unique both in terms of sensitivity and usability, mainly due to the well-known unique properties of the europium label. This communication demonstrates the use of this new method in distinguishing different wines, waters, alcohols, and artificially modified berry juices.

Development of an International Odor Identification Test for Children: The Universal Sniff Test

Objective To assess olfactory function in children and to create and validate an odor identification test to diagnose olfactory dysfunction in children, which we called the Universal Sniff (U‐Sniff) test. Study design This is a multicenter study involving 19 countries. The U‐Sniff test was developed in 3 phases including 1760 children age 5‐7 years. Phase 1: identification of potentially recognizable odors; phase 2: selection of odorants for the odor identification test; and phase 3: evaluation of the test and acquisition of normative data. Test—retest reliability was evaluated in a subgroup of children (n = 27), and the test was validated using children with congenital anosmia (n = 14). Results Twelve odors were familiar to children and, therefore, included in the U‐Sniff test. Children scored a mean ± SD of 9.88 ± 1.80 points out of 12. Normative data was obtained and reported for each country. The U‐Sniff test demonstrated a high test—retest reliability (r27 = 0.83, P < .001) and enabled discrimination between normosmia and children with congenital anosmia with a sensitivity of 100% and specificity of 86%. Conclusions The U‐Sniff is a valid and reliable method of testing olfaction in children and can be used internationally.

Self-Ratings of Olfactory Performance and Odor Annoyance Are Associated With the Affective Impact of Odor, but Not With Smell Test Results.

Our aim was to explore factors potentially associated with subjective (self-rated) and objective (measured using the Sniffin’ Sticks Extended test) olfactory performance in the general population without olfactory disorders. We studied associations between olfactory performance and how important odors were in determining liking for new places, things, and people (measured using the Affective Impact of Odor scale) and the average annoyance caused by odors in 117 adults (83 women, 34 men; age 18–69 years, mean age 32 years). In a subset of 44 participants, we also studied associations between olfactory performance and spice odor identification task scores (14 odors) and the number of herbs and spices consumed. Self-rated olfactory acuity and odor-related annoyance were associated with the Affective Impact of Odor scores, but neither correlated with the smell test results. Instead, the number of spices consumed correlated with spice odor identification score (r = .50) and the identification (but not threshold nor discrimination) subscore of the Sniffin’ Sticks test (r = .49). Our results suggest that a tendency to perceive odors in affective terms may be associated with overestimation of olfactory abilities and that recurrent exposure to a large variety of spice odors may improve performance on odor identification.