Heritability of cigarette smoking and alcohol use in Chinese male twins: the Qingdao twin registry

Gene-environment transactions between peer cigarette use, parental supervision, and Chinese adolescent cigarette smoking initiation

INTRODUCTION

The initiation and continued use of tobacco products constitute an ongoing source of preventable disease that continues to pose a significant risk to global adolescent health. Scarce research has sought to explore the influences of two well-known environmental risk factors, parental supervision and peer cigarette use, on genetic and environmental contributions to adolescent cigarette use, especially in non-Western populations.

METHODS

Following 602 Chinese twin pairs (52% female, N = 1204) from early to middle adolescence at two-time points (Mage = 12 and 15) from 2006 to 2009 and using multivariate biometric modeling, this study examined gene-environment interplay (i.e., gene-environment correlation and interaction) between perceived parental supervision, peer cigarette use, and adolescent cigarette smoking initiation.

RESULTS

From early to middle adolescence, genetic influences on cigarette smoking initiation became more pronounced, whereas shared environmental influences that promote similarity between family members diminished. Genetic factors primarily explained the links between parental supervision and cigarette smoking initiation in mid-adolescence. Peer cigarette use displayed stronger associations with and moderating potential in adolescent cigarette smoking initiation than parental supervision. High levels of peer cigarette use amplified genetic risk for cigarette smoking initiation in mid-adolescence.

CONCLUSIONS

Chinese adolescent cigarette smoking initiation involves dynamic gene-environment transactions primarily with peer processes over development. Mid-adolescence constitutes a developmental period wherein underlying genetic risk for cigarette smoking initiation is particularly sensitive to peer influences. Targeted interventions aimed at reducing Chinese adolescent cigarette smoking initiation should focus on peer processes during this developmental period.

Loci on chromosome 20 interact with rs16969968 to influence cigarettes per day in European ancestry individuals

BACKGROUND

The understanding of the molecular genetic contributions to smoking is largely limited to the additive effects of individual single nucleotide polymorphisms (SNPs), but the underlying genetic risk is likely to also include dominance, epistatic, and gene-environment interactions.

METHODS

To begin to address this complexity, we attempted to identify genetic interactions between rs16969968, the most replicated SNP associated with smoking quantity, and all SNPs and genes across the genome.

RESULTS

Using the UK Biobank European subsample, we found one SNP, rs1892967, and two genes, PCNA and TMEM230, that showed a significant genome-wide interaction with rs16969968 for log10 CPD and raw CPD, respectively, in a sample of 116 442 individuals who self-reported currently or previously smoking. We extended these analyses to individuals of South Asian descent and meta-analyzed the combined sample of 117 212 individuals of European and South Asian ancestry. We replicated the gene findings in a meta-analysis of five Finnish samples (N=40 140): FinHealth, FINRISK, Finnish Twin Cohort, GeneRISK, and Health-2000-2011.

CONCLUSIONS

To our knowledge, this represents the first reliable epistatic association between single nucleotide polymorphisms for smoking behaviors and provides a novel direction for possible future functional studies related to this interaction. Furthermore, this work demonstrates the feasibility of these analyses by pooling multiple datasets across various ancestries, which may be applied to other top SNPs for smoking and/or other phenotypes.

Genetic and shared couple environmental contributions to smoking and alcohol use in the UK population

Alcohol use and smoking are leading causes of death and disability worldwide. Both genetic and environmental factors have been shown to influence individual differences in the use of these substances. In the present study we tested whether genetic factors, modelled alongside common family environment, explained phenotypic variance in alcohol use and smoking behaviour in the Generation Scotland (GS) family sample of up to 19,377 individuals. SNP and pedigree-associated effects combined explained between 18 and 41% of the variance in substance use. Shared couple effects explained a significant amount of variance across all substance use traits, particularly alcohol intake, for which 38% of the phenotypic variance was explained. We tested whether the within-couple substance use associations were due to assortative mating by testing the association between partner polygenic risk scores in 34,987 couple pairs from the UK Biobank (UKB). No significant association between partner polygenic risk scores were observed. Associations between an individual's alcohol PRS (b = 0.05, S.E. = 0.006, p < 2 × 10-16) and smoking status PRS (b = 0.05, S.E. = 0.005, p < 2 × 10-16) were found with their partner's phenotype. In support of this, G carriers of a functional ADH1B polymorphism (rs1229984), known to be associated with greater alcohol intake, were found to consume less alcohol if they had a partner who carried an A allele at this SNP. Together these results show that the shared couple environment contributes significantly to patterns of substance use. It is unclear whether this is due to shared environmental factors, assortative mating, or indirect genetic effects. Future studies would benefit from longitudinal data and larger sample sizes to assess this further.

Immune Trait Shifts in Association With Tobacco Smoking: A Study in Healthy Women

Tobacco smoking is known to impact circulating levels of major immune cells populations, but its effect on specific immune cell subsets remains poorly understood. Here, using high-resolution data from 223 healthy women (25 current and 198 never smokers), we investigated the association between smoking status and 35,651 immune traits capturing immune cell subset frequencies. Our results confirmed that active tobacco smoking is associated with increased frequencies of circulating CD8+ T cells expressing the CD25 activation marker. Moreover, we identified novel associations between smoking status and relative abundances of CD8+ CD25+ memory T cells, CD8+ memory T cells expressing the CCR4 chemokine receptor, and CD4+CD8+ (double-positive) CD25+ T cells. We also observed, in current smokers, a decrease in the relative frequencies of CD4+ T cells expressing the CD38 activation marker and an increase in class-switched memory B cell isotypes IgA, IgG, and IgE. Finally, using data from 135 former female smokers, we showed that the relative frequencies of immune traits associated with active smoking are usually completely restored after smoking cessation, with the exception of subsets of CD8+ and CD8+ memory T cells, which persist partially altered. Our results are consistent with previous findings and provide further evidence on how tobacco smoking shapes leukocyte cell subsets proportion toward chronic inflammation.

Reduced Cortical Thickness in the Right Caudal Middle Frontal Is Associated With Symptom Severity in Betel Quid-Dependent Chewers

BACKGROUND

Findings from brain structural imaging studies on betel quid dependence have supported relations between betel quid chewing and alterations in gray matter volume and white matter integrity. However, the effect of betel quid chewing on cortical thickness and the link between cortical thickness and symptom severity remains unascertained.

METHODS

In this observational study, we compared cortical thickness measures from 24 male betel quid-dependent chewers with 27 male healthy controls. Using FreeSufer, we obtained three-dimensional T1-weighted images that were used to compute the thickness of the cerebral cortex throughout the cortical layer.

RESULTS

Compared to healthy controls, betel quid dependent chewers displayed significant decreased cortical thickness in the precuneus, entorhinal, right paracentral, middle temporal, and caudal middle frontal gyri. Betel quid dependence scale scores negatively correlated (r = -0.604; p = 0.002) with reduced cortical thickness in the right caudal middle frontal of betel quid-dependent chewers.

CONCLUSION

The findings provide evidence for cortical thickness abnormality in betel dependent chewers and further propose that the severity of betel quid symptoms may be a critical aspect associated with the cortical alterations. The observed alterations may serve as potential mechanisms to explain why BQ chewing behavior is persistent among individuals with betel quid dependence.

SNPs in NRXN1 and CHRNA5 are associated to smoking and regulation of GABAergic and glutamatergic pathways

AIM

To identify genetic variants associated with greater tobacco consumption in a Mexican population.

PATIENTS & METHODS

Daily smokers were classified as light smokers (LS; n = 742), heavy smokers (HS; n = 601) and nonsmokers (NS; n = 606). In the first stage, a genotyping microarray that included 347 SNPs in CHRNA2-CHRNA7/CHRNA10, CHRNB2-CHRNB4 and NRXN1 genes and 37 ancestry-informative markers was used to analyze 707 samples (187 HS, 328 LS and 192 NS). In the second stage, 14 SNPs from stage 1 were validated in the remaining samples (HS, LS and NS; n = 414 in each group) using real-time PCR. To predict the role of the associated SNPs, an in silico analysis was performed.

RESULTS

Two SNPs in NRXN1 and two in CHRNA5 were associated with cigarette consumption, while rs10865246/C (NRXN1) was associated with high nicotine addiction. The in silico analysis revealed that rs1882296/T had a high level of homology with Hsa-miR-6740-5p, which encodes a putative miRNA that targets glutamate receptor subunits (GRIA2, GRID2) and GABA receptor subunits (GABRG1, GABRA4, GABRB2), while rs1882296/C had a high level of homology with Hsa-miR-6866-5p, which encodes a different miRNA that targets GRID2 and GABRB2.

CONCLUSION

In a Mexican Mestizo population, greater consumption of cigarettes was influenced by polymorphisms in the NRXN1 and CHRNA5 genes. We proposed new hypotheses regarding the putative roles of miRNAs that influence the GABAergic and glutamatergic pathways in smoking addiction.

Crucial roles of the CHRNB3-CHRNA6 gene cluster on chromosome 8 in nicotine dependence: update and subjects for future research

Cigarette smoking is a leading cause of preventable death throughout the world. Nicotine, the primary addictive compound in tobacco, plays a vital role in the initiation and maintenance of its use. Nicotine exerts its pharmacological roles through nicotinic acetylcholine receptors (nAChRs), which are ligand-gated ion channels consisting of five membrane-spanning subunits. Besides the CHRNA4, CHRNB2 and CHRNA5/A3/B4 cluster on chromosome 15, which has been investigated intensively, recent evidence from both genome-wide association studies and candidate gene-based association studies has revealed the crucial roles of the CHRNB3-CHRNA6 gene cluster on chromosome 8 in nicotine dependence (ND). These studies demonstrate two distinct loci within this region. The first one is tagged by rs13277254, upstream of the CHRNB3 gene, and the other is tagged by rs4952, a coding single nucleotide polymorphism in exon 5 of that gene. Functional studies by genetic manipulation in mice have shown that α6*-nAChRs, located in the ventral tegmental area (VTA), are of great importance in controlling nicotine self-administration. However, when the α6 subunit is selectively re-expressed in the VTA of the α6(-/-) mouse by a lentiviral vector, the reinforcing property of nicotine is restored. To further determine the role of α6*-nAChRs in the process of nicotine-induced reward and withdrawal, genetic knock-in strains have been examined, which showed that replacement of Leu with Ser in the 9' residue in the M2 domain of α6 produces nicotine-hypersensitive mice (α6 L9'S) with enhanced dopamine release. Moreover, nicotine-induced upregulation may be another ingredient in the pathology of nicotine addiction although the effect of chronic nicotine exposure on the expression of α6-containing receptors is controversial. To gain a better understanding of the pathological processes underlying ND and ND-related behaviors and to promote the development of effective smoking cessation therapies, we here present the most recent studies concerning the genetic effects of the CHRNB3-CHRNA6 gene cluster in ND.

Contribution of Variants in CHRNA5/A3/B4 Gene Cluster on Chromosome 15 to Tobacco Smoking: From Genetic Association to Mechanism

Cigarette smoking is the major cause of preventable death and morbidity throughout the world. Many compounds are present in tobacco, but nicotine is the primary addictive one. Nicotine exerts its physiological and pharmacological roles in the brain through neuronal nicotinic acetylcholine receptors (nAChRs), which are ligand-gated ion channels consisting of five membrane-spanning subunits that can modulate the release of neurotransmitters, such as dopamine, glutamate, and GABA and mediate fast signal transmission at synapses. Considering that there are 12 nAChR subunits, it is highly likely that subunits other than α4 and β2, which have been intensively investigated, also are involved in nicotine addiction. Consistent with this hypothesis, a number of genome-wide association studies (GWAS) and subsequent candidate gene-based associated studies investigating the genetic variants associated with nicotine dependence (ND) and smoking-related phenotypes have shed light on the CHRNA5/A3/B4 gene cluster on chromosome 15, which encodes the α5, α3, and β4 nAChR subunits, respectively. These studies demonstrate two groups of risk variants in this region. The first one is marked by single nucleotide polymorphism (SNP) rs16969968 in exon 5 of CHRNA5, which changes an aspartic acid residue into asparagine at position 398 (D398N) of the α5 subunit protein sequence, and it is tightly linked SNP rs1051730 in CHRNA3. The second one is SNP rs578776 in the 3'-untranslated region (UTR) of CHRNA3, which has a low correlation with rs16969968. Although the detailed molecular mechanisms underlying these associations remain to be further elucidated, recent findings have shown that α5* (where "*" indicates the presence of additional subunits) nAChRs located in the medial habenulo-interpeduncular nucleus (mHb-IPN) are involved in the control of nicotine self-administration in rodents. Disruption of α5* nAChR signaling diminishes the aversive effects of nicotine on the mHb-IPN pathway and thereby permits more nicotine consumption. To gain a better understanding of the function of the highly significant genetic variants identified in this region in controlling smoking-related behaviors, in this communication, we provide an up-to-date review of the progress of studies focusing on the CHRNA5/A3/B4 gene cluster and its role in ND.

Familial aggregation of tobacco use behaviors among Amish men

INTRODUCTION

Tobacco use is a complex behavior. The Old Order Amish community offers unique advantages for the study of tobacco use because of homogenous ancestral background, sociocultural similarity, sex-specific social norms regarding tobacco use, and large family size. Tobacco use in the Old Order Amish community is almost exclusively confined to males.

METHODS

We examined characteristics of tobacco use and familial aggregation among 1,216 Amish males from cross-sectional prospectively collected data. Outcomes examined included ever using tobacco regularly, current use, quantity of use, duration of use, and frequency of use.

RESULTS

Sixteen percent of Amish men were current tobacco users, with the majority reporting cigar use only. Higher rates of tobacco use were found among sons of fathers who smoked compared with sons of fathers who did not smoke (46% vs. 22%, p < .001) as well as among brothers of index cases who smoked compared with brothers of index cases who did not smoke (61% vs. 29%, p < .001). After controlling for shared household effects and age, heritability accounted for 66% of the variance in ever smoking regularly (p = .045).

CONCLUSIONS

The familial patterns of tobacco use observed among Amish men highlight the important role of family in propagating tobacco use and support the usefulness of this population for future genetic studies of nicotine addiction.

The China Seven Cities Study (CSCS) consortium: adapting evidence-based prevention science from west to east

Chronic, noncommunicable diseases (NCDs) have surpassed infectious diseases as the primary cause of death and disability in most developing nations. Nowhere is this more evident than in China where NCDs account for 80% of all deaths and skyrocketing medical costs. Driving the escalation of NCDs are high rates of tobacco use, longer life spans, and changes in the traditional Chinese diet and lifestyle bolstered by unprecedented economic growth and the new global culture. Despite the epidemic of NCDs, few evidence-based interventions either to prevent or retard their progression exist in China. We present a case for the development and adoption of such strategies as effective tools to combat China's greatest health threat. Finally, we offer an example of a collaborative network linking Chinese public health and academic institutions with US researchers to promote the translation of western evidence-based interventions that fully incorporate local knowledge, culture, and capacity.

Familial effects on survival after myocardial infarction: a registry-based sib-pair study

The chance of surviving an acute myocardial infarction (MI) has increased greatly but many persons still die as a consequence of MI. We assessed the familiality of suffering fatal MI using Swedish registry data. All 4,239 sib-pairs (n = 8,478) where both siblings had suffered an MI and who were born 1932 or later were identified by matching the Swedish National Patient-, Cause of Death and Multi-Generation registries. The Cox proportional hazards model was used to estimate the association between survival times between sibling who had, or not had, a sibling who died within 28 days of their first MI. The risk estimate was adjusted for year of infarction, age at infarction, sex and county for both siblings. The mortality rate was increased the first 28 days after infarction amongst patients who had a sibling who also died within 28 days of infarction (adjusted Hazard ratio (HR) [95 % confidence interval [95 % CI]: 1.44 [1.18-1.75]). These patients also have a worse long-term survival (adjusted HR [95 % CI]: 1.65 [1.24-2.21]). There appears to be familial effects that influence MI survival. This may have important implications for MI prevention strategies but further studies are required to determine if these effects are due to genetic or environmental factors.

The genetic correlation between cigarette smoking and alcohol drinking among Chinese adult male twins: an ordinal bivariate genetic analysis

BACKGROUND

Though multiple policies have been implemented, the cigarette control in China is still facing a great challenge. At the same time, alcohol drinking has increasingly become a public health problem. Considering cigarette smoking and alcohol drinking often co-occur, a few studies tested the covariance of these phenotypes. However, the genetic and environmental correlation between them among Chinese population has not been determined. The main aim of this study is to fill this gap.

METHODS

From the Chinese National Twin Registry, we obtained the data on cigarette smoking and alcohol drinking behaviors. The ordinal bivariate genetic analysis was performed to fit the categorical variables. After identifying the best decomposition among the Cholesky, common, and independent pathway model, we established the most parsimonious submodel.

RESULTS

The correlation between current tobacco and alcohol use could be explained by Cholesky model. The shared environmental variances for both phenotypes were dropped to construct the most parsimonious submodel. Furthermore, the most parsimonious submodel showed a moderate correlation (0.32, 95%CI=0.17-0.46) between the genetic components and a negligible non-shared environmental correlation.

CONCLUSION

As the first bivariate genetic analysis on current tobacco smoking and current alcohol drinking in China, this study suggested a common genetic vulnerability to tobacco and alcohol use in male twins. Further studies should be carried out to track the pertinent genes that are related to the comorbidity of smoking and drinking in Chinese population. Another urgent need is to recognize the behavior-specific environmental risk factors.

The CHRNA5-A3-B4 gene cluster in nicotine addiction

Nicotine addiction (NA) is a common and devastating disease, such that the annual number of deaths (world-wide) from tobacco-related diseases will double from 5 million in the year 2000 to 10 million in 2020. Nicotine is the only substance in tobacco which animals and humans will self-administer. NA, as a lifetime diagnosis, has been assessed in various approaches, including the concept of cigarettes per day (CPD). Other assessments of NA are somewhat more comprehensive, such as the Fagerstrom Test for Nicotine Dependence or the American Psychiatric Association's Diagnostic and Statistical Manual (fourth edition) diagnosis of nicotine dependence. These different measures have moderate agreement with one another. Twin, family and adoption studies have shown that these different assessments of NA have substantial heritability (that fraction of risk attributable to genetic factors). The heritability of NA has been estimated at 50-75%, depending on the definition and the population under study. DNA-based studies of NA have been somewhat successful in identifying a common haplotype, which increases risk for NA among European-origin populations. This haplotype explains a small amount of variance, accounting for ∼1 CPD, and it includes the α5 and the α3 nicotinic receptor subunit genes (CHRNA5 and CHRNA3). The review will focus on this implicated region. In this risk region, there is a common (among European-origin people) mis-sense single-nucleotide polymorphism in the CHRNA5 gene (D398N), which changes a conserved amino acid from aspartic acid to asparagine. The risk allele (398N) confers decreased calcium permeability and more extensive desensitization, according to in vitro cellular studies, raising the possibility that a positive allosteric modulator of the (α4β2)(2)α5 type of nicotinic receptor might have therapeutic potential in NA. There are other genetic influences on NA in this region, apart from the mis-sense variant, and additional biological experiments must be done to understand them.

Genetic and environmental etiology of nicotine use in Sri Lankan male twins

Little is known about the prevalence and etiology of tobacco use in Asian populations. This study aims to test whether the finding of substantial heritability for tobacco-related phenotypes in Western populations is generalizable to developing countries. The twin method was used to estimate the relative contribution of genetic and environmental influences on nicotine-related phenotypes. Participants were selected from the population based Sri Lankan Twin Registry. The Composite International Diagnostic Interview was administered to 1,804 male individuals to assess five phenotypes: nicotine use; desire and unsuccessful attempts to quit smoking; subjective feeling of being tobacco dependent; and two DSM-IV diagnoses; nicotine dependence and nicotine withdrawal. Almost one-third of the male twins were life-time smokers. The genetic results were consistent with the previously reported findings from Western and Chinese populations, in that the nicotine use traits were significantly heritable, with environmental influences being of the non-shared nature. The results derived from the Causal Contingent Common pathway model (CCC) supported previous findings that show that liabilities to regular smoking and subsequent problem smoking have both shared and specific genetic influences.

Genome-wide meta-analyses of smoking behaviors in African Americans

The identification and exploration of genetic loci that influence smoking behaviors have been conducted primarily in populations of the European ancestry. Here we report results of the first genome-wide association study meta-analysis of smoking behavior in African Americans in the Study of Tobacco in Minority Populations Genetics Consortium (n = 32,389). We identified one non-coding single-nucleotide polymorphism (SNP; rs2036527[A]) on chromosome 15q25.1 associated with smoking quantity (cigarettes per day), which exceeded genome-wide significance (β = 0.040, s.e. = 0.007, P = 1.84 × 10(-8)). This variant is present in the 5'-distal enhancer region of the CHRNA5 gene and defines the primary index signal reported in studies of the European ancestry. No other SNP reached genome-wide significance for smoking initiation (SI, ever vs never smoking), age of SI, or smoking cessation (SC, former vs current smoking). Informative associations that approached genome-wide significance included three modestly correlated variants, at 15q25.1 within PSMA4, CHRNA5 and CHRNA3 for smoking quantity, which are associated with a second signal previously reported in studies in European ancestry populations, and a signal represented by three SNPs in the SPOCK2 gene on chr10q22.1. The association at 15q25.1 confirms this region as an important susceptibility locus for smoking quantity in men and women of African ancestry. Larger studies will be needed to validate the suggestive loci that did not reach genome-wide significance and further elucidate the contribution of genetic variation to disparities in cigarette consumption, SC and smoking-attributable disease between African Americans and European Americans.

Genetic analyses of smoking initiation, persistence, quantity, and age-at-onset of regular cigarette use in Brazilian families: the Baependi Heart Study

BACKGROUND

The purpose of this study was to estimate the genetic influences on the initiation of cigarette smoking, the persistence, quantity and age-at-onset of regular cigarette use in Brazilian families.

METHODS

The data set consisted of 1,694 individuals enrolled in the Baependi Heart Study. The heritability and the heterogeneity in genetic and environmental variance components by gender were estimated from variance components approaches, using the SOLAR (Sequential Oligogenic Linkage Analysis Routines) computer package. The mixed-effects Cox model was used for the genetic analysis of the age-at onset of regular cigarette use.

RESULTS

The heritability estimates were high (> 50%) for smoking initiation and were intermediate, ranging from 23.4 to 31.9%, for smoking persistence and quantity. Significant evidence for heterogeneity in variance components by gender was observed for smoking initiation and age-at-onset of regular cigarette use. Genetic factors play an important role in the interindividual variation of these phenotypes in females, while in males there is a predominant environmental component, which could be explained by greater social influences in the initiation of tobacco use.

CONCLUSIONS

Significant heritabilities were observed in smoking phenotypes for both males and females from the Brazilian population. These data add to the literature and are concordant with the notion of significant biological determination in smoking behavior. Samples from the Baependi Heart Study may be valuable for the mapping of genetic loci that modulate this complex biological trait.

Genetics of schizophrenia and smoking: an approach to studying their comorbidity based on epidemiological findings

The association between schizophrenia and tobacco smoking has been described in more than 1,000 articles, many with inadequate methodology. The studies on this association can focus on: (1) current smoking, ever smoking or smoking cessation; (2) non-psychiatric controls or controls with severe mental illness (e.g., bipolar disorder); and (3) higher smoking frequency or greater usage in smokers. The association with the most potential for genetic studies is that between ever daily smoking and schizophrenia; it may reflect a shared genetic vulnerability. To reduce the number of false-positive genes, we propose a three-stage approach derived from epidemiological knowledge. In the first stage, only genetic variations associated with ever daily smoking that are simultaneously significant within the non-psychiatric controls, the bipolar disorder controls and the schizophrenia cases will be selected. Only those genetic variations that are simultaneously significant in the three hypothesis tests will be tested in the second stage, where the prevalence of the genes must be significantly higher in schizophrenia than in bipolar disorder, and significantly higher in bipolar disorder than in controls. The genes simultaneously significant in the second stage will be included in a third stage where the gene variations must be significantly more frequent in schizophrenia patients who did not start smoking daily until their 20s (late start) versus those who had an early start. Any genetic approach to psychiatric disorders may fail if attention is not given to comorbidity and epidemiological studies that suggest which comorbidities are likely to be explained by genetics and which are not. Our approach, which examines the results of epidemiological studies on comorbidities and then looks for genes that simultaneously satisfy epidemiologically suggested sets of hypotheses, may also apply to the study of other major illnesses.

Heritabilities of Alcohol Use Disorders Identification Test (AUDIT) scores and alcohol biomarkers in Koreans: the KoGES (Korean Genome Epi Study) and Healthy Twin Study

BACKGROUND

Both the Alcohol Use Disorders Identification Test (AUDIT) and alcohol biomarkers are used to screen for alcohol problems. The purpose of this study was to examine the genetic and environmental contributions to the AUDIT score and alcohol biomarkers in Koreans.

METHODS

The study included 1678 current alcohol drinkers: 818 Korean twins and 860 their families. The Korean version of AUDIT and alcohol biomarkers, i.e., gamma glutamyltransferase (GGT), alanine aminotransferase (ALT), mean corpuscular volume (MCV), and triglycerides (TG), were studied. The analyses were conducted using variance components method to estimate heritability and common environmental effects, and bivariate analyses for genetic and environmental correlations between the AUDIT score and the biomarkers after adjustment for age, gender, interaction of age and gender, smoking status, the amount of consumed alcohol, body mass index, and education.

RESULTS

Heritabilities for the AUDIT score were 0.35 and 0.40-0.71 for biomarkers (P<0.001). The risk of alcohol problems using AUDIT score was positively associated with the levels of biomarkers (GGT, MCV, and TG) in men, while the relationship was significant only for MCV in women. Genetic or environmental correlations between the AUDIT score and some of the biomarkers (GGT and MCV) were significant in men, but not significant in women.

CONCLUSIONS

We found a significant genetic contribution to the AUDIT score and the alcohol biomarkers. As there were significant genetic and environmental relationships between the AUDIT score and the alcohol biomarkers in men, future studies are warranted to identify common genes and environmental effects affecting the relationships.

Heritability of smoking, alcohol use, and psychological characteristics among adolescent twins in Qingdao, China

BACKGROUND

Previous studies of genetic and environmental influences on adolescent substance use have been limited to Western samples.

METHODS

This study assesses genetic and environmental contributions to cigarette smoking, alcohol use, and psychological variables (depression, anxiety, aggression, hostility) among 602 pairs of adolescent twins, 11 to 19 years old, in Qingdao, China.

RESULTS

Heritable influences were more pronounced for alcohol use than cigarette smoking. In univariate analyses, no heritable effects were found for depression or aggression, and modest heritability was found for anxiety. Hostility was relatively more heritable in girls than boys. Bivariate associations between substance use and psychological measures could be attributed to a combination of common genetic and environmental factors.

CONCLUSIONS

Among Chinese adolescents, experimentation with tobacco is familial, and experimentation with alcohol is heritable. The genetic and environmental architecture of hostility differs by gender. Consistency of univariate results with Western adolescent samples appears limited to the alcohol use measures.

Are there genetic influences on addiction: evidence from family, adoption and twin studies

AIMS

In this exciting era of gene discovery, we review evidence from family, adoption and twin studies that examine the genetic basis for addiction. With a focus on the classical twin design that utilizes data on monozygotic and dizygotic twins, we discuss support in favor of heritable influences on alcohol, nicotine, cannabis and other illicit drug dependence.

METHODS

We review whether these genetic factors also influence earlier stages (e.g. experimentation) of the addictive process and whether there are genetic influences specific to each psychoactive substance.

RESULTS

Converging evidence from these studies supports the role of moderate to high genetic influences on addiction with estimates ranging from 0.30 to 0.70. The changing role of these heritable factors as a function of gender, age and cultural characteristics is also discussed. We highlight the importance of the interplay between genes and the environment as it relates to risk for addiction and the utility of the children-of-twins design for emerging studies of gene-environment interaction is presented.

CONCLUSIONS

Despite the advances being made by low-cost high-throughput whole genome association assays, we posit that information garnered from twin studies, especially extended twin designs with power to examine gene-environment interactions, will continue to form the foundation for genomic research.

Alpha-5/alpha-3 nicotinic receptor subunit alleles increase risk for heavy smoking

Twin studies indicate that additive genetic effects explain most of the variance in nicotine dependence (ND), a construct emphasizing habitual heavy smoking despite adverse consequences, tolerance and withdrawal. To detect ND alleles, we assessed cigarettes per day (CPD) regularly smoked, in two European populations via whole genome association techniques. In these approximately 7500 persons, a common haplotype in the CHRNA3-CHRNA5 nicotinic receptor subunit gene cluster was associated with CPD (nominal P=6.9 x 10(-5)). In a third set of European populations (n= approximately 7500) which had been genotyped for approximately 6000 SNPs in approximately 2000 genes, an allele in the same haplotype was associated with CPD (nominal P=2.6 x 10(-6)). These results (in three independent populations of European origin, totaling approximately 15 000 individuals) suggest that a common haplotype in the CHRNA5/CHRNA3 gene cluster on chromosome 15 contains alleles, which predispose to ND.

Norepinephrine transporter polymorphisms T-182C and G1287A are not associated with alcohol dependence and its clinical subgroups

Several studies have suggested that the norepinephrine transporter (NET) may play an important role in the pathogenesis of alcohol dependence. Additional studies have shown that the polymorphisms of T-182C (rs2242446) and G1287A (rs5569) in NET gene (hSLC6A2) may affect the NET function. Therefore, in this study, we examined whether these hSLC6A2 gene polymorphisms are a susceptibility factor for alcohol dependence or its clinical subgroup(s). A total of 690 Han Chinese subjects (408 alcohol dependent patients and 282 controls) in Taiwan were recruited for this study. Individuals with alcohol dependence were classified into several clinical subgroups to reduce the clinical heterogeneity. All subjects were interviewed with identical methods, and the mental disorders were diagnosed according to DSM-IV criteria. The polymorphisms of T-182C and G1287A in hSLC6A2 gene were analyzed by using a standard method. No significant differences in genotype and allele frequencies of hSLC6A2 polymorphisms were found between controls and total alcohol dependence or between more homogeneous subgroups with alcohol dependence and controls. This study suggests that the polymorphisms of T-182C and G1287A in hSLC6A2 gene are not major risk factors in increasing susceptibility to either alcohol dependence or its clinical subtypes.

Genetics of nicotine dependence and pharmacotherapy

Nicotine dependence is substantially heritable. Several regions across the genome have been implicated in containing genes that confer liability to nicotine dependence and variation in individual genes has been associated with nicotine dependence. Smoking cessation measures are also heritable, and measured genetic variation is associated with nicotine dependence treatment efficacy. Despite significant strides in the understanding of the relative contribution of genetic and environmental factors to nicotine dependence and treatment, emergent challenges necessitate interdisciplinary coordinated effort for effective problem solving. These challenges include refinement of the nicotine dependence phenotype, better understanding of the dynamic interplay between genes and environment in nicotine dependence etiology, application and development of molecular and statistical methodology that can adequately address vast amounts of data, and continuous translational cross-talk.