Association of serum cotinine level with a cluster of three nicotinic acetylcholine receptor genes (CHRNA3/CHRNA5/CHRNB4) on chromosome 15.

A cluster of three nicotinic acetylcholine receptor genes on chromosome 15 (CHRNA5/CHRNA3/CHRNB4) has been shown to be associated with nicotine dependence and smoking quantity. The aim of this study was to clarify whether the variation at this locus regulates nicotine intake among smokers by using the level of a metabolite of nicotine, cotinine, as an outcome. The number of cigarettes smoked per day (CPD) and immune-reactive serum cotinine level were determined in 516 daily smokers (age 30-75 years, 303 males) from the population-based Health2000 study. Association of 21 SNPs from a 100 kb region of chromosome 15 with cotinine and CPD was examined. SNP rs1051730 showed the strongest association to both measures. However, this SNP accounted for nearly a five-fold larger proportion of variance in cotinine levels than in CPD (R(2) 4.3% versus 0.9%). The effect size of the SNP was 0.30 for cotinine level, whereas it was 0.13 for CPD. Variation at CHRNA5/CHRNA3/CHRNB4 cluster influences nicotine level, measured as cotinine, more strongly than smoking quantity, measured by CPD, and appears thus to be involved in regulation of nicotine levels among smokers.

Twin study of heritability of eating bread in Danish and Finnish men and women.

Bread is an elementary part of the western diet, and especially rye bread is regarded as an important source of fibre. We investigated the heritability of eating bread in terms of choice of white and rye bread and use-frequency of bread in female and male twins in Denmark and Finland. The study cohorts included 575 Danish (age range 18-67 years) and 2009 Finnish (age range 22-27 years) adult twin pairs. Self-reported frequency of eating bread was obtained by food frequency questionnaires. Univariate models based on linear structural equations for twin data were used to estimate the relative magnitude of the additive genetic, shared environmental and individual environmental effects on bread eating frequency and choice of bread. The analysis of bread intake frequency demonstrated moderate heritability ranging from 37-40% in the Finnish cohort and 23-26% in the Danish cohort. The genetic influence on intake of white bread was moderate (24-31%), while the genetic influence on intake of rye bread was higher in men (41-45%) than in women (24-33%). Environmental influences shared by the twins were not significant. Consumption of bread as well as choice of bread is influenced by genetic predisposition. Environmental factors shared by the co-twins (e.g., childhood environment) seem to have no significant effects on bread consumption and preference in adulthood.

Environmental effects exceed genetic effects on perceived intensity and pleasantness of several odors: a three-population twin study.

Human genes encoding odorant receptors have been identified, but the contribution of genetic effects to total variation in specific odor perceptions is largely unknown. We estimated the relative contributions of genetic and environmental effects to variation in the perceived intensity and pleasantness of cinnamon, chocolate, turpentine, and isovaleric acid (sweaty) odors by quantitative genetic modeling of odor rating data from 856 twin individuals (including 83 complete monozygotic and 275 dizygotic twin pairs) aged 10-60 years (44% males and 56% females) from Australia, Denmark, and Finland. Results from fitting univariate models including components for additive genetic (A), shared environmental (C), and non-shared environmental (E) effects to the data implied that non-shared environmental effects account for the most variation in ratings of individual odors while genetic effects play only a minor role. Multivariate independent pathway model revealed a modest but significant common additive genetic component for intensity ratings, explaining 18% of the total variation. The results promote the importance of inter-individual variation in odor exposures and olfactory plasticity to odor perception.

Genetic and environmental contributions to food use patterns of young adult twins.

The contribution of genetic factors to individual differences in food use was estimated in a large population-based twin cohort of young adults (22- to 27-year-old). Male and female twins (n=2009 complete twin pairs) evaluated use-frequencies of 24 food items using 5 categories (1=never-5=several times a day) in a postal questionnaire. Foods were categorized by factor analysis. Estimates of the relative proportions of additive genetic, shared environmental, and unshared environmental effects on the use-frequency of food items and factor scores were obtained by quantitative genetic modeling of twin data based on linear structural equations. Four factors of food use were identified: "healthy" foods, high-fat foods, sweet foods, and meats. The variance of the use-frequency of food items and food categories was explained by additive genetic and unshared environmental influences, whereas shared environmental factors did not contribute to food use. The average proportions of genetic effects on the total variance of the use-frequency of food items and food categories were 40% and 45%, respectively. Sex differences were observed in the magnitude of genetic influences for use-frequency of four food items (chocolate, other sweets, fried foods, and meat), and in genetic factors underlying the use of three (fresh vegetables, fruits, and cheeses) items. In conclusion, family environment does not appear to influence the food use of young adults and thus nutritional education should be targeted at this age group to support development of healthy eating patterns. In addition, the results illuminate the importance of the sex-specific genetic effects on food use.

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 (h(2)=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 (h(2)=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.

Same genetic components underlie different measures of sweet taste preference.

BACKGROUND: Sweet taste preferences are measured by several often correlated measures. OBJECTIVE: We examined the relative proportions of genetic and environmental effects on sweet taste preference indicators and their mutual correlations. DESIGN: A total of 663 female twins (324 complete pairs, 149 monozygous and 175 dizygous pairs) aged 17-80 y rated the liking and intensity of a 20% (wt/vol) sucrose solution, reported the liking and the use-frequency of 6 sweet foods (sweet desserts, sweets, sweet pastry, ice cream, hard candy, and chocolate), and completed a questionnaire on cravings of sweet foods. The estimated contributions of genetic factors, environmental factors shared by a twin pair, and environmental factors unique to each twin individual to the variance and covariance of the traits were obtained with the use of linear structural equation modeling. RESULTS: Approximately half of the variation in liking for sweet solution and liking and use-frequency of sweet foods (49-53%) was explained by genetic factors, whereas the rest of the variation was due to environmental factors unique to each twin individual. Sweet taste preference-related traits were correlated. Tetravariate modeling showed that the correlation between liking for the sweet solution and liking for sweet foods was due to genetic factors (genetic r = 0.27). Correlations between liking, use-frequency, and craving for sweet foods were due to both genetic and unshared environmental factors. CONCLUSION: Detailed information on the associations between preference measures is an important intermediate goal in the determination of the genetic components affecting sweet taste preferences.

Sweet taste preferences are partly genetically determined: identification of a trait locus on chromosome 16.

BACKGROUND: Humans have an innate preference for sweet taste, but the degree of liking for sweet foods varies individually. OBJECTIVE: The proportion of inherited sweet taste preference was studied. A genome-wide linkage analysis was performed to locate the underlying genetic elements in the genome. DESIGN: A total of 146 subjects (32% men, 68% women) aged 18-78 y from 26 Finnish families evaluated the intensity and pleasantness of 3 suprathreshold solutions of sucrose (3.0%, 7.5%, and 18.75%) and plain water and the intensity of filter paper impregnated with 6-n-propylthiouracil (PROP). The subjects also reported the pleasantness and the use frequency of 5 sweet foods (chocolate, candy, ice cream, sweet desserts, and sweet pastry) and completed a food-behavior questionnaire that measured their craving for sweet foods. RESULTS: Of the chemosensory functions, the pleasantness rating of the strongest (18.75%) sucrose solution and the intensity rating of PROP yielded the highest heritability estimates (41% and 66%, respectively). The pleasantness and the use frequency of sweet foods (both variables calculated as a mean of ratings for 5 food items) and the craving for sweet foods showed significant heritability (40%, 50%, and 31%, respectively). A logarithm of odds score of 3.5 (P=0.00003) was detected for use frequency of sweet foods on chromosome 16p11.2 (marker D16S753). CONCLUSIONS: Sweet taste preferences are partly inherited. Chromosome 16p11.2 may harbor genetic variations that affect the consumption of sweet foods.

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.

Sequence variants at CHRNB3-CHRNA6 and CYP2A6 affect smoking behavior.

Smoking is a common risk factor for many diseases. We conducted genome-wide association meta-analyses for the number of cigarettes smoked per day (CPD) in smokers (n = 31,266) and smoking initiation (n = 46,481) using samples from the ENGAGE Consortium. In a second stage, we tested selected SNPs with in silico replication in the Tobacco and Genetics (TAG) and Glaxo Smith Kline (Ox-GSK) consortia cohorts (n = 45,691 smokers) and assessed some of those in a third sample of European ancestry (n = 9,040). Variants in three genomic regions associated with CPD (P < 5 x 10(-8)), including previously identified SNPs at 15q25 represented by rs1051730[A] (effect size = 0.80 CPD, P = 2.4 x 10(-69)), and SNPs at 19q13 and 8p11, represented by rs4105144[C] (effect size = 0.39 CPD, P = 2.2 x 10(-12)) and rs6474412-T (effect size = 0.29 CPD, P = 1.4 x 10(-8)), respectively. Among the genes at the two newly associated loci are genes encoding nicotine-metabolizing enzymes (CYP2A6 and CYP2B6) and nicotinic acetylcholine receptor subunits (CHRNB3 and CHRNA6), all of which have been highlighted in previous studies of smoking and nicotine dependence. Nominal associations with lung cancer were observed at both 8p11 (rs6474412[T], odds ratio (OR) = 1.09, P = 0.04) and 19q13 (rs4105144[C], OR = 1.12, P = 0.0006).

The Three-Factor Eating Questionnaire, body mass index, and responses to sweet and salty fatty foods: a twin study of genetic and environmental associations.

BACKGROUND: The relation between body weight and energy-dense foods remains unclear. OBJECTIVE: We estimated the effects of genetic and environmental factors on cognitive and emotional aspects of dieting behavior, body mass index (BMI), and responses to fatty foods and on their relations. DESIGN: A total of 1326 adult twin persons (aged 17-82 y; 17% M and 83% F) from the United Kingdom and Finland completed the revised version of the Three-Factor Eating Questionnaire (TFEQ-R18) and reported the liking and use-frequency of 4 sweet-and-fatty and salty-and-fatty food items (6 items in the United Kingdom and 5 items in Finland). Genetic modeling was done by using linear structural equations. RESULTS: Heritability estimates were calculated separately for the countries and sexes; they were 26-63% for cognitive restraint, 45-69% for uncontrolled eating, and 9-45% for emotional eating, respectively. Of the variation in liking and use-frequency of fatty foods, 24-54% was attributed to interindividual genetic differences. No significant correlations were observed between BMI and fatty food use or liking. However, BMI was positively (mostly genetically) correlated (genetic r = 0.16-0.51) with all of the dieting behaviors, and they correlated with fatty food use and liking ratings. Uncontrolled eating was both genetically and environmentally associated with liking for salty-and-fatty foods (genetic and environmental r = 0.16), and emotional eating was genetically associated with liking for sweet-and-fatty foods (genetic r = 0.31). CONCLUSIONS: The relation between BMI and diet appears to be mediated through dieting behaviors. Dietary counseling should focus on unhealthy dieting behaviors rather than only on direct advice on food use.

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. PARTICIPANTS AND METHODS: A total of 1,311 individual twins from the general population (62% females and 38% males, aged 10-83 years, mean age 29 years) including 191 monozygous and 343 dizygous complete twin pairs from Australia, Denmark, Finland, and the United Kingdom rated their sense of smell and annoyance caused by ambient smells (e.g., smells of foods) using seven categories, and performed odor identification and evaluation task for six scratch-and-sniff odor stimuli. RESULTS: The self-rating of olfactory function correlated with the self-rating of odor annoyance (r = 0.30) but neither correlated with the odor identification score. Quantitative genetic modeling revealed no unambiguously significant genetic contribution to variation in any of the studied traits. CONCLUSION: The results suggest that environmental rather than genetic factors modify the self-rating of olfactory function and support earlier findings of discrepancy between subjective and objective measures of olfactory function. In addition, the results imply that the self-rating of olfactory function arises from experienced odor annoyance rather than from actual olfactory acuity.