A twin study of non-alcohol substance abuse

Investigating the Associations among Drug Dependents' Family Function and Exercise Attitudes: Marital Status Differences

This paper examines: (1) The demographic characteristics of different marital statuses of drug dependents; (2) differences in exercise attitudes and family function by marital status; and (3) if family function factors correlated with exercise attitudes and if exercise attitude factors correlated with family function. Multivariate analyses of variance (MANOVAs) revealed significant differences in drug dependents’ exercise attitudes between married and single groups (p < 0.05) and the married and “other” groups (p < 0.01). Furthermore, we observed significant differences in drug dependents’ family function between married and single groups (p < 0.01) and married and other groups (p < 0.05). Regression analyses indicated that communication [F_change(1,1791) = 137.819; p < 0.001] was a significant positive predictor for drug dependents’ exercise attitude, accounting for 7.1% of the observed variance. Moreover, 50% of the variance was explained by willingness [F_change(1,1791) = 850.49, p < 0.001] and control [F_change(1,1790) = 141.415, p < 0.001], which were two significant predictors of drug dependents’ family function. Findings of this study were: (1) Exercise attitude and family function of married drug dependents were better than single drug dependents and other marital status addicts; (2) communication was observed as a factor of family function that correlated with exercise attitude; and (3) willingness was related with family function.

Recent advances with 5-HT3 modulators for neuropsychiatric and gastrointestinal disorders

Serotonin (5-hydroxytryptophan [5-HT]) is a biologically active amine expressed in platelets, in gastrointestinal (GI) cells and, to a lesser extent, in the central nervous system (CNS). This biogenic compound acts through the activation of seven 5-HT receptors (5-HT_1-7 Rs). The 5-HT₃ R is a ligand-gated ion channel belonging to the Cys-loop receptor family. There is a wide variety of 5-HT₃ R modulators, but only receptor antagonists (known as setrons) have been used clinically for chemotherapy-induced nausea and vomiting and irritable bowel syndrome treatment. However, since the discovery of the setrons in the mid-1980s, a large number of studies have been published exploring new potential applications due their potency in the CNS and mild side effects. The results of these studies have revealed new potential applications, including the treatment of neuropsychiatric disorders such as schizophrenia, depression, anxiety, and drug abuse. In this review, we provide information related to therapeutic potential of 5-HT₃ R antagonists on GI and neuropsychiatric disorders. The major attention is paid to the structure, function, and pharmacology of novel 5-HT₃ R modulators developed over the past 10 years.

Reserpine differentially affects cocaine-induced behavior in low and high responders to novelty

Individuals are known to differ in their sensitivity to cocaine. Cocaine is known to inhibit the re-uptake of monoamines. The response to cocaine has also been found to depend on monoamines inside reserpine-sensitive storage vesicles. The present study examined the effects of reserpine (1-2 mg/kg) on cocaine-induced behavior (10-15 mg/kg) in Low Responders (LR) and High Responders (HR) to novelty rats. LR displayed less cocaine-induced walking, wall rearing, free rearing and stereotyped behavior than HR did. The dose of 1 mg/kg of reserpine decreased cocaine-induced walking, wall rearing, free rearing and stereotyped behavior in LR, but not in HR. A dose of 2 mg/kg of reserpine was required to inhibit cocaine-induced behavior in HR. Combining these behavioral findings with our previously reported neurochemical finding that a higher dose of reserpine was required to inhibit the accumbal dopamine response to cocaine in HR than in LR (Verheij et al., 2008), suggests that HR are more sensitive to the behavioral effects of cocaine than LR because cocaine can release more monoamines from storage vesicles in HR than in LR. Our behavioral data also demonstrate that the individual differences in sensitivity to reserpine are not only limited to the dopaminergic system of the nucleus accumbens.

Rats that differentially respond to cocaine differ in their dopaminergic storage capacity of the nucleus accumbens

Cocaine (COC) inhibits the re-uptake of dopamine. However, the dopamine response to COC also depends on dopamine inside storage vesicles. The aim of this study was to investigate whether rats that differentially respond to COC differ in their dopaminergic storage capacity of the nucleus accumbens. Total and vesicular levels of accumbal dopamine as well as accumbal vesicular monoamine transporter-2 levels were established in high (HR) and low responders (LR) to novelty rats. Moreover, the effects of reserpine (RES) on the COC-induced increase of extracellular accumbal dopamine were investigated. HR displayed higher accumbal levels of total and vesicular dopamine than LR. Moreover, HR displayed more accumbal vesicular monoamine transporters-2 than LR. COC increased extracellular accumbal dopamine more strongly in HR than in LR. A low dose of RES prevented the COC-induced increase of accumbal dopamine in LR, but not in HR. A higher dose of RES was required to inhibit the COC-induced increase of accumbal dopamine in HR. These data demonstrate that HR were marked by a larger accumbal dopaminergic storage pool than LR. It is hypothesized that HR are more sensitive to COC than LR, because COC can release more dopamine from accumbal storage vesicles in HR than in LR.

J. Neurochem. (2008) 105, 2122–2133.

Genetic association studies of methamphetamine use disorders: A systematic review and synthesis

Efforts to understand the biological processes that increase susceptibility to methamphetamine (METH) use disorders (i.e., abuse, dependence, and psychosis) have uncovered several putative genotypic variants. However, to date a synthesis of this information has not been conducted. Thus, systematic searches of the current literature were undertaken for genetic-association studies of METH use disorders. Each gene's chromosomal location, function, and examined polymorphic markers were extracted. Frequencies, odds ratios and 95% confidence intervals for risk alleles, as well as sample size and power, were calculated. We uncovered 38 studies examining 39 genes, of which 18 were found to have a significant genotypic, allelic, and/or haplotypic association with METH use disorders. Three genes (COMT, DRD4, and GABRA1) were associated with METH abuse, nine (ARRB2, BDNF, CYP2D6, GLYT1, GSTM1, GSTP1, PDYN, PICK1, and SLC22A3) with METH dependence, two (AKT1 and GABRG2) with METH abuse/dependence, and four (DTNBP1, OPRM1, SNCA, and SOD2) with METH psychosis. Limitations related to phenotypic classification, statistical power, and potential publication bias in the current literature were noted. Similar to other behavioral, psychiatric, and substance use disorders, the genetic epidemiology of METH use disorders is complex and likely polygenic. National and international collaborative efforts are needed to increase the availability of large population-based samples and improve upon the power to detect genetic associations of small magnitude. Further, replication of the findings reviewed here along with further development of more rigorous methodologies and reporting protocols will aid in delineating the complex genetic epidemiology of METH use disorders.

Smoking and smoking cessation in disadvantaged women: assessing genetic contributions

Abundant evidence from family, adoption and twin studies points to large genetic contributions to individual differences in vulnerability to develop dependence on one or more addictive substances, including tobacco. Twin data suggests that much of this genetic vulnerability is shared by individuals who are dependent on a variety of addictive substances. Interestingly, some twin data also supports substantial differences in the apparent heritability of nicotine dependence in women as environmental conditions become more permissive for their smoking. In addition, twin studies also support the idea that ability to quit smoking displays substantial heritability, and that this heritable influence overlaps partially with genetic influences on nicotine dependence. Candidate gene molecular genetic studies and genome wide association studies of substance dependence and ability to quit smoking each document apparent polygenic influences that identify lists of genes that display partial overlap, as expected from classical genetic studies. More of these genes are expressed in the brain than would be anticipated by chance. These lists of genes overlap significantly with those identified in molecular genetic studies of individual differences in cognitive abilities, frontal lobe brain volumes as well as personality and psychiatric phenotypes. Though most available genome wide association data do not separate results by gender, it may be notable that few of these genes lie on sex chromosomes. These data provide a substrate to improve understanding of nicotine dependence, the ability to quit smoking, the potential for less permissive environments to restrict the expression of genetic influences on smoking and the possibility that brain features that underlie phenotypes such as individual differences in cognitive abilities might interact with environmental features that are especially prominent for disadvantaged women to provide special circumstances that should be considered in prevention and treatment efforts to reduce smoking.

Intermediate cannabis dependence phenotypes and the FAAH C385A variant: an exploratory analysis

RATIONALE

Cannabis dependence is a growing problem among individuals who use marijuana frequently, and genetic differences make some users more liable to progress to dependence. The identification of intermediate phenotypes of cannabis dependence may aid candidate genetic analysis. Promising intermediate phenotypes include craving for marijuana, withdrawal symptoms after abstinence, and sensitivity to its acute effects. A single nucleotide polymorphism (SNP) in the gene encoding for fatty acid amide hydrolase (FAAH) has demonstrated association with substance use disorder diagnoses, but has not been studied with respect to these narrower phenotypes. FAAH is an enzyme that inactivates anandamide, an endogenous agonist for CB(1) receptors (to which Delta(9)-tetrahydrocannabinol binds). CB(1) binding modulates mesocorticolimbic dopamine release, which underlies many facets of addiction.

OBJECTIVES

The SNP, FAAH C385A (rs324420), was examined to determine whether its variance was associated with changes in craving and withdrawal after marijuana abstinence, craving after cue exposure, or sensitivity to the acute effects of marijuana.

MATERIALS AND METHODS

Forty daily marijuana users abstained for 24 h, were presented with a cue-elicited craving paradigm and smoked a marijuana cigarette in the laboratory.

RESULTS

C385A variance was significantly associated with changes in withdrawal after abstinence, and happiness after smoking marijuana in the predicted directions, was associated with changes in heart rate after smoking in the opposite of the predicted direction, and was not associated with changes in craving or other acute effects.

CONCLUSIONS

These data lend support to some previous association studies of C385A, but suggest that further refinement of these intermediate phenotypes is necessary.

Addiction genetics and pleiotropic effects of common haplotypes that make polygenic contributions to vulnerability to substance dependence

Abundant evidence from family, adoption, and twin studies point to large genetic contributions to individual differences in vulnerability to develop dependence on one or more addictive substances. Twin data suggest that most of this genetic vulnerability is shared by individuals who are dependent on a variety of addictive substances. Molecular genetic studies, especially genomewide and candidate gene association studies, have elucidated common haplotypes in dozens of genes that appear to make polygenic contributions to vulnerability to developing dependence. Most genes that harbor currently identified addiction-associated haplotypes are expressed in the brain. Haplotypes in many of the same genes are identified in genomewide association studies that compare allele frequencies in substance dependent vs. control individuals from European, African, and Asian racial/ethnic backgrounds. Many of these addiction-associated haplotypes display pleiotropic influences on a variety of related brain-based phenotypes that display 1) substantial heritability and 2) clinical cooccurence with substance dependence.

Molecular genetics of addiction and related heritable phenotypes: genome-wide association approaches identify "connectivity constellation" and drug target genes with pleiotropic effects

Genome-wide association (GWA) can elucidate molecular genetic bases for human individual differences in complex phenotypes that include vulnerability to addiction. Here, we review (a) evidence that supports polygenic models with (at least) modest heterogeneity for the genetic architectures of addiction and several related phenotypes; (b) technical and ethical aspects of importance for understanding GWA data, including genotyping in individual samples versus DNA pools, analytic approaches, power estimation, and ethical issues in genotyping individuals with illegal behaviors; (c) the samples and the data that shape our current understanding of the molecular genetics of individual differences in vulnerability to substance dependence and related phenotypes; (d) overlaps between GWA data sets for dependence on different substances; and (e) overlaps between GWA data for addictions versus other heritable, brain-based phenotypes that include bipolar disorder, cognitive ability, frontal lobe brain volume, the ability to successfully quit smoking, neuroticism, and Alzheimer's disease. These convergent results identify potential targets for drugs that might modify addictions and play roles in these other phenotypes. They add to evidence that individual differences in the quality and quantity of brain connections make pleiotropic contributions to individual differences in vulnerability to addictions and to related brain disorders and phenotypes. A "connectivity constellation" of brain phenotypes and disorders appears to receive substantial pathogenic contributions from individual differences in a constellation of genes whose variants provide individual differences in the specification of brain connectivities during development and in adulthood. Heritable brain differences that underlie addiction vulnerability thus lie squarely in the midst of the repertoire of heritable brain differences that underlie vulnerability to other common brain disorders and phenotypes.

Marijuana withdrawal and craving: influence of the cannabinoid receptor 1 (CNR1) and fatty acid amide hydrolase (FAAH) genes

AIM

To examine whether withdrawal after abstinence and cue-elicited craving were associated with polymorphisms within two genes involved in regulating the endocannabinoid system, cannabinoid receptor 1 (CNR1) and fatty acid amide hydrolase (FAAH). Two single nucleotide polymorphisms (SNPs) in the CNR1 (rs2023239) and FAAH (rs324420) genes, associated previously with substance abuse and functional changes in cannabinoid regulation, were examined in a sample of daily marijuana smokers.

PARTICIPANTS

Participants were 105 students at the University of Colorado, Boulder between the ages of 18 and 25 years who reported smoking marijuana daily.

MEASUREMENTS

Participants were assessed once at baseline and again after 5 days of abstinence, during which they were exposed to a cue-elicited craving paradigm. Outcome measures were withdrawal and craving collected using self-reported questionnaires. In addition, urine samples were collected at baseline and on day 5 for the purposes of 11-nor-9-carboxy-Delta9-tetrahydrocannabinol (THC-COOH) metabolite analysis.

FINDINGS

Between the two sessions, THC-COOH metabolite levels decreased significantly, while measures of withdrawal and craving increased significantly. The CNR1 SNP displayed a significant abstinence x genotype interaction on withdrawal, as well as a main effect on overall levels of craving, while the FAAH SNP displayed a significant abstinence x genotype interaction on craving.

CONCLUSIONS

These genetic findings may have both etiological and treatment implications. However, longitudinal studies will be needed to clarify whether these genetic variations influence the trajectory of marijuana use/dependence. The identification of underlying genetic differences in phenotypes such as craving and withdrawal may aid genetically targeted approaches to the treatment of cannabis dependence.

Genetic and environmental contributions to the diversity of substances used in adolescent twins: a longitudinal study of age and sex effects

AIMS

To determine how genetic and environmental contributions affecting the number of psychoactive substances used varies with age and gender over the course of adolescence.

DESIGN

Estimates of genetic, shared environmental and non-shared environmental contributions to total variance in diversity of substances used at ages 11, 14 and 17 years were obtained by fitting a multivariate behavior genetic (Cholesky) model.

PARTICIPANTS

A total of 711 male and 675 female twins.

MEASUREMENTS

Participants reported whether they had used each of 11 substances.

FINDINGS

The average diversity of substances used increased over time for both males and females, and males generally reported a wider diversity of substances used than females. Influences of genetic factors increased with age and were greater for males than for females at ages 14 and 17 years. Genetic factors remained consistent (i.e. highly correlated) across ages for both males and females, as did shared environmental influences for males. Non-shared environmental factors for both sexes and females' shared environmental factors were age-specific.

CONCLUSIONS

Regardless of sex, the proportion of variance in substances used attributable to genetic factors increases during adolescence, although it is greater for males than females at later ages. These findings indicate that prevention interventions may be most effective if they target early adolescence when environmental factors account for the majority of variance in substance use. The high correlation of genetic factors across ages suggests that early use may sometimes signal an early expression of a developmentally stable genetic predisposition.

Variation in a bicarbonate co-transporter gene family member SLC4A7 is associated with propensity to addictions: a study using fine-mapping and three samples

AIMS

Classical genetic studies consistently reveal substantial heritability for addictions. However, the genes that harbour the variations providing these genetic influences remain largely unknown. We have focused attention on 'reproducible substance abuse vulnerability' (rSA) genomic regions, where linkage and association studies performed in several population provide evidence for such variations.

DESIGN

We nominated rSA1 on human chromosome 3p23 within a 5 Mb region. We sought to replicate this finding and identify variations within this region.

SETTING

We examine the role of allelic variations in the SLC4A7 gene, a member of the bicarbonate co-transporter family that is expressed in tissues including brain and kidney.

PARTICIPANTS

A total of 1158 unrelated individuals with informed consent about the genetic study were recruited from three independent populations.

MEASUREMENTS

The single nucleotide polymorphism (SNP) markers in the SLC4A7 gene were analysed by case-control study.

FINDINGS

The rs3278 is associated reliably with substance abuse vulnerability in (1) a European American sample selected from pedigrees within the Collaborative Study on the Genetics of Alcoholism (COGA; nominal P = 0.03); (2) an African American sample recruited by the National Institute on Drug Abuse (NIDA; nominal P = 0.008); and (3) a NIDA European American sample (P = 0.001).

CONCLUSIONS

While the current results do not exclude additional roles for allelic variants in nearby genes, they do suggest that SLC4A7 allelic variants might alter dispositions and/or excretion of drugs and neurotransmitters in brain and periphery in ways that could contribute to differential vulnerabilities to addictions. SLC4A7 is thus a novel candidate in the contribution to vulnerability to addictions.

"Higher order" addiction molecular genetics: convergent data from genome-wide association in humans and mice

Family, adoption and twin data each support substantial heritability for addictions. Most of this heritable influence is not substance-specific. The overlapping genetic vulnerability for developing dependence on a variety of addictive substances suggests large roles for "higher order" pharamacogenomics in addiction molecular genetics. We and others have now completed genome-wide association (GWA) studies of DNAs from individuals with dependence on a variety of addictive substances versus appropriate controls. Recently reported replicated GWA observations identify a number of genes based on comparisons between controls and European-American and African-American polysubstance abusers. Here we review the convergence between these results and data that compares control samples and (a) alcohol-dependent European-Americans, (b) methamphetamine-dependent Asians and (c) nicotine dependent samples from European backgrounds. We also compare these human data to quantitative trait locus (QTL) results from studies of addiction-related phenotypes in mice that focus on alcohol, methamphetamine and barbiturates. These comparisons support a genetic architecture built from largely polygenic contributions of common allelic variants to dependence on a variety of legal and illegal substances. Many of the gene variants identified in this way are likely to alter specification and maintenance of neuronal connections.

Heritability of illicit drug use and transition to dependence in Southwest California Indians

OBJECTIVE

Native Americans have high rates of drug use and dependence yet little is known concerning its etiology or clinical course. These analyses were conducted to describe the heritability of the use of a variety of illicit drugs, as well as the conditional probability of transitioning from use to dependence for each drug class in a community sample of Native American men and women.

METHODS

The sample included 460 participants (190 men and 270 women), recruited through community effort, from eight contiguous Indian reservations in Southern California. Participants were assessed using the Semi-Structured Assessment for the Genetics of Alcoholism. The Semi-Structured Assessment for the Genetics of Alcoholism interview retrospectively asks about the initial use and drug dependence of the following illicit drug classes: marijuana, cocaine, stimulants, sedatives, opiates, hallucinogens, and solvents. Heritability of initial use was determined using SOLAR (http://www.sfbr.org/solar/).

RESULTS

Ninety-one percent of this select Indian population had tried at least one of the illicit drug classes. The most commonly tried substance was marijuana (88%), followed by stimulants (60%), cocaine (44%), hallucinogens (34%), and solvents (20%). The heritability of initiation of drug use ranged from 0.14 for cocaine to 0.59 for marijuana. The conditional probability of transition from initiation to drug dependence ranged from 0.66 for stimulants to 0.06 for hallucinogens.

CONCLUSIONS

These findings suggest that heritability of the initiation of substance use, in Southwest California Indians, may be similar to other population samples. In this population, however, high rates of dependence on marijuana, opiates, and stimulants are seen once initiation of the use of the substance has occurred.

Substance use disorder (SUD) morbidity versus number of parents with SUD

OBJECTIVES

To assess the association between numbers of parents (i.e., 0, 1 or 2) with Substance Use Disorder (SUD) and proband's SUD severity and morbidity.

DESIGN

Descriptive, cross-sectional.

SETTINGS

Alcohol-drug treatment programs in two university medical centers.

SUBJECTS

597 voluntary patients aged 18 and older with SUD; adoptees excluded.

RESULTS

On univariate analysis, parental SUD was associated with ten characteristics. On logistic regression analysis, having any parental SUD was associated with lower socioeconomic status, younger age at using tobacco, more severity on M-SAPS, and lower psychosocial function in the last year (Axis 5) as threshold effects. Logistic regression analysis comparing 1 versus 2 parents with SUD showed that those with 2 SUD parents began using alcohol at an earlier age as compared with having 1 SUD parent; this was an additive effect.

CONCLUSIONS

Parental SUD affects the proband's SUD severity in a threshold fashion.

Age of first marijuana use and the occurrence of marijuana use disorders in Southwest California Indians

In several national surveys a younger age of substance usage has been associated with a higher likelihood of the development of dependence. Some studies have suggested that age at first use is primarily an environmentally driven variable, whereas others suggest that it may be partially mediated by a general vulnerability to exhibit problem behaviors. Although Native Americans, overall, have the highest prevalence of substance dependence of any US ethnic group, the relationship of age of first marijuana use on the development of dependence in Native American populations is relatively unknown. Demographic information and DSM-III-R diagnoses were obtained from 525 Southwest California Indian adults residing on contiguous reservations. Multinomial logistic regression was used to investigate the relationship between age of first use and marijuana use disorders. Early marijuana use was found to be strongly associated with abuse and dependence in this population, even in the presence of several other risk factors including externalizing diagnoses. These data suggest that effective environmental prevention efforts at reducing early marijuana use may be an important strategy to lower the prevalence of use disorders in this high risk population.

Pooled association genome scanning for alcohol dependence using 104,268 SNPs: validation and use to identify alcoholism vulnerability loci in unrelated individuals from the collaborative study on the genetics of alcoholism

Association genome scanning can identify markers for the allelic variants that contribute to vulnerability to complex disorders, including alcohol dependence. To improve the power and feasibility of this approach, we report validation of "100k" microarray-based allelic frequency assessments in pooled DNA samples. We then use this approach with unrelated alcohol-dependent versus control individuals sampled from pedigrees collected by the Collaborative Study on the Genetics of Alcoholism (COGA). Allele frequency differences between alcohol-dependent and control individuals are assessed in quadruplicate at 104,268 autosomal SNPs in pooled samples. One hundred eighty-eight SNPs provide (1) the largest allele frequency differences between dependent versus control individuals; (2) t values >or= 3 for these differences; and (3) clustering, so that 51 relatively small chromosomal regions contain at least three SNPs that satisfy criteria 1 and 2 above (Monte Carlo P = 0.00034). These positive SNP clusters nominate interesting genes whose products are implicated in cellular signaling, gene regulation, development, "cell adhesion," and Mendelian disorders. The results converge with linkage and association results for alcohol and other addictive phenotypes. The data support polygenic contributions to vulnerability to alcohol dependence. These SNPs provide new tools to aid the understanding, prevention, and treatment of alcohol abuse and dependence.

Age at First Intoxication and Alcohol Use Disorders in Southwest California Indians

BACKGROUND

In several national surveys, a younger age of onset of first drink and/or regular drinking has been associated with a higher likelihood of the development of alcohol dependence. Some studies have suggested that age at first drink is primarily an environmentally driven variable whereas others suggest that it may be partially mediated by a general vulnerability to exhibit problem behaviors. Although Native Americans, overall, have the highest prevalence of alcohol dependence of any U.S. ethnic group, the relationship of age of onset of intoxication with alcohol dependence in Native American populations is relatively unknown.

METHODS

Demographic information and DSM-III-R diagnoses were obtained from 525 Southwest California (SWC) Indian adults residing on contiguous reservations. Survival analyses and Cox and logistic regression were used to investigate the relationship between age of onset of first intoxication and the development of alcohol dependence. Heritability of the age of onset of first intoxication was also determined using SOLAR.

RESULTS

Age at first intoxication was not found to be heritable in this population. Early onset of intoxication, however, was found to be significantly associated with both a shorter time to onset of alcohol dependence and increased prevalence in this population, even on taking into account several other risk factors including externalizing diagnoses.

CONCLUSIONS

These data suggest that effective environmental prevention efforts at reducing underage drinking may be an important strategy to lower the prevalence of alcohol dependence in this high-risk population.

Comorbidity between alcohol dependence and illicit drug dependence in adolescents with antisocial behavior and matched controls

BACKGROUND

Knowledge regarding the causes of comorbidity among substance use disorders can have significant impact on future research examining the etiology of these disorders. Unfortunately, the conclusions of past studies examining the comorbidity among substance use disorders are conflicting; some studies emphasize familial influences common to multiple substances, while others emphasize substance-specific influences. Discrepancies in results may reflect different analytical approaches or differences in the samples. Here, we examine the causes of comorbidity between alcohol dependence and illicit drug dependence in adolescents.

METHODS

We ascertained a clinical sample of adolescents treated for antisocial behavior and substance use disorders and their siblings and a matched control sample. A model fitting approach was used to test 13 alternative hypotheses for the causes of comorbidity.

RESULTS

The best supported hypothesis for the comorbidity between alcohol dependence and illicit drug dependence was a model hypothesizing that comorbid disorders are alternate forms of a single underlying liability. The next best fitting models were two of the correlated liabilities models (correlated risk factors and reciprocal causation).

DISCUSSION

The results suggest that the best hypotheses explaining the comorbidity between alcohol and illicit drug dependence in adolescents are that alcohol dependence and illicit drug dependence are manifestations of a single general liability to develop substance dependence or that there are separate liabilities that are highly correlated.

NrCAM in addiction vulnerability: positional cloning, drug-regulation, haplotype-specific expression, and altered drug reward in knockout mice

Several lines of evidence support roles for the cell adhesion molecule NrCAM in addictions. Fine mapping within a chromosome 7 region that contains previously linked and associated genomic markers identifies NrCAM haplotypes that are associated with substance abuse vulnerabilities in four samples of abusers and controls. Differential display identifies NrCAM as a drug regulated gene. NrCAM is expressed in neurons linked to reward and memory. NrCAM displays haplotype-specific gene expression in human post-mortem brain samples. Knockout mice display reduced opiate- and stimulant-conditioned place preferences. These observations support NrCAM as a positionally cloned and drug-regulated gene whose variants are likely to change expression and alter substance abuse vulnerabilities in human addictions and animal models of drug reward.

Pooled association genome scanning: validation and use to identify addiction vulnerability loci in two samples

Association genome scanning is of increasing interest for identifying the chromosomal regions that contain gene variants that contribute to vulnerability to complex disorders, including addictions. To improve the power and feasibility of this approach, we have validated "10k" microarray-based allelic frequency assessments in pooled DNA samples and have used this approach to seek allelic frequency differences between heavy poly-substance abusers and well characterized control individuals. Thirty-eight loci contain SNPs that display robust allele frequency differences between abusers and controls in both European- and African-American samples. These loci identify an alcohol/acetaldehyde dehydrogenase gene cluster and genes implicated in cellular signaling, gene regulation, development, "cell adhesion," and Mendelian disorders. The results converge with previous linkage and association results for addictions. Pooled association genome scanning provides a useful tool for elucidating molecular genetic underpinnings of complex disorders and identifies both previously understood and previously unanticipated mechanisms for addiction vulnerability.

The Washington University Twin Study of alcoholism

Genetic contributions to the liability to develop alcoholism in males of Northern and Western European ancestry are well-established. However, questions remain concerning the role of genetic variation in the etiology of alcoholism among non-white populations, among women, and the possibility of etiological heterogeneity in subtypes of alcoholism. The answers to these questions are needed to help define phenotypes for molecular genetic studies searching for QTLs for alcoholism. Twins from 295 pairs were consecutively ascertained at inpatient and outpatient psychiatric and alcohol treatment facilities in St. Louis, MO in 1981-1986. Probands and willing cotwins were evaluated by structured psychiatric interviews, psychometric assessment, and lifetime treatment records. One hundred fifty-four probands met criteria for alcohol abuse/dependence (AAD), including twins from 45 MZ, 50 same-sex DZ, and 59 opposite-sex pairs. Twin-pair resemblance was evaluated for AAD and alcohol dependence (AD), as well as for subsets defined by gender, patterns of comorbidity, ethnic background, and clinical features. Among males, heritability of AAD and AD was substantial, with little evidence for common environmental contributions to family resemblance. Pair resemblance among females was also substantial, but similar for MZ and DZ pairs, yielding near-zero heritability estimates. However, based on these sample sizes, the sex differences were not statistically significant. The results confirm prior studies of strong genetic influences on alcoholism in males, but suggest lower genetic influence in females. Power to test other sources of heterogeneity was limited, but the results suggest no evidence for higher heritability for male early onset alcoholism or for alcoholism with comorbid antisocial personality.

Genetic segregation analysis of alcohol and other substance-use disorders in families with recurrent, early-onset major depression

OBJECTIVE

The goal of this study was to conduct a complex segregation analysis of alcohol and other substance-use disorders in families identified by probands with recurrent, early-onset major depression (RE-MDD).

METHOD

Eighty-one families were identified through probands over the age of 18, who met criteria for recurrent (> or = 2 episodes), early-onset (< or = 25 years), nonpsychotic, unipolar major depression (RE-MDD) and included 407 first-degree relatives and 835 extended relatives. Psychiatric diagnoses for probands and their family members who provided blood samples were formulated from structured personal interviews, structured family history assessments, and available medical records. The remaining family members who participated and those who were deceased were evaluated through the family history method augmented by available medical records. Best estimate diagnoses were made during a consensus conference according to established diagnostic criteria. Segregation analyses were performed using the REGD routine in S.A.G.E. release 4.0.

RESULTS

The best-fitting models for the transmission of "alcohol use disorders" or "alcohol/other substance use disorders" were sex-dependent Mendelian recessive models with significant residual spousal effects. Moreover, the parameter estimates for the models were very similar for these phenotypes. In contrast, the segregation analysis of "substance use disorder" supported a transmissible, but non-Mendelian, major effect.

CONCLUSIONS

Our results suggest that a major locus contributes to the expression of alcohol use disorders or alcohol/other substance-use disorders within families identified by probands with RE-MDD. Due to the limitations of the segregation analysis model, our results cannot address whether the same major locus is segregating across families in our sample or whether multiple major loci are involved (genetic heterogeneity). Previous studies supported single gene transmission of recurrent major depression and major mood disorders in these families [Marazita et al. Am. J. Hum. Genet. 1997, 61, 1370-1378; Maher et al. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 2002. 114 (2), 214-221]. Mounting evidence suggests that at.least some of this "comorbidity" may result from the effects of shared susceptibility genes or an overlap in the sets of genes that contribute to the vulnerability of developing these mental disorders [Zubenko, G.S. Mol. Psychiatry 2000, 5, 131-136].

Substance abuse vulnerability loci: converging genome scanning data

Classical genetic studies suggest strong complex genetic contributions to a predisposition to abuse multiple addictive substances. Until recently, there were no reproducible genome scanning data identifying chromosomal positions likely to contain allelic variants that predispose the carrier to illegal substance addiction. Nominal results of linkage-based genome scanning studies for ethanol and nicotine addictions failed to display much agreement. Our recent data from association-based genome scans for illegal addictions, and reanalyses of previous results now provide a substantial body of converging results. The 15 reproducible chromosomal loci identified here are good candidates to harbor allelic variants that alter human substance abuse vulnerabilities. We discuss several approaches to identifying the specific gene variants that underlie these convergent association and linkage observations, and the impact that these convergent observations should have on understanding important human addictive disorders.

Polysubstance abuse-vulnerability genes: genome scans for association, using 1,004 subjects and 1,494 single-nucleotide polymorphisms

Strong genetic contributions to drug abuse vulnerability are well documented, but few chromosomal locations for human drug-abuse vulnerability alleles have been confirmed. We now identify chromosomal markers whose alleles distinguish drug abusers from control individuals in each of two samples, on the basis of pooled-sample microarray and association analyses. Reproducibly positive chromosomal regions defined by these markers in conjunction with previous results were especially unlikely to have been identified by chance. Positive markers identify the alcohol dehydrogenase (ADH) locus, flank the brain-derived neurotropic factor (BDNF) locus, and mark seven other regions previously linked to vulnerability to nicotine or alcohol abuse. These data support polygenic contributions of common allelic variants to polysubstance abuse vulnerability.

Adolescent illegal drug use: the impact of personality, family, and environmental factors

This study examined the relationship between the domains of environmental factors, family illegal drug use, parental child-rearing practices, maternal and adolescent personality attributes, and adolescent illegal drug use. A nonclinical sample of 2,837 Colombian youths and their mothers were interviewed about intrapersonal, interpersonal, and environmental factors in their lives. Results indicated that certain environmental factors (e.g., violence, drug availability, and machismo), family drug use, a distant parent-child relationship, and unconventional behavior are risk factors for adolescent illegal drug use. As hypothesized, results showed that the adverse effects of family illegal drug use on adolescent drug use can be buffered by protective parental child-rearing practices and environmental factors, leading to less adolescent illegal drug use. Prevention and treatment efforts should incorporate protective environmental, familial, and intrapersonal components in order to reduce adolescent illegal drug use.

Family history influence on drug abuse severity and treatment outcome

Influence of parental alcohol/substance abuse on methadone maintenance therapy (MMT) outcome was examined in 164 DSM-III-R opioid dependent adults with no other current DSM Axis I disorder. Family history positive patients had more DSM-III-R opioid dependence symptoms and were more likely to be classified as severely dependent. However, when placed on identical daily doses of methadone (50 mg), they had lower rates of illicit opioid use but higher rates of cocaine use than family history negative patients. Both effects remained significant after adjusting for gender and race. These results suggest that common genetic factors may underlie both susceptibility to heroin dependence and response to therapeutic methadone treatment.

Genetic and environmental influences on drug use and abuse/dependence in male and female twins

Twins were recruited through alcohol and drug treatment programs. With structural equation modeling, genetic and environmental estimates were obtained for use and DSM-III abuse/dependence of sedatives, opioids, cocaine, stimulants, and cannabis as well as any illicit drug. Analyses were conducted separately for males and females. Models included thresholds based on population prevalence of use or abuse/dependence and ever having been in treatment. Genetic influences were found for most measures. They were generally stronger for males than females and for clinical diagnoses of abuse/dependence compared to use. Common environmental influences played a greater role in use than abuse/dependence.

Differential Susceptibility to Comorbid Drug Abuse and Violence

Although many psychoactive substances have been associated with violent behavior, only a subgroup manifests excessively aggressive behavior when sober or intoxicated. Theories to explain addictive behaviors in general may directly relate to the specific proclivity to exhibit excessive aggression in this subset of users. Certain personality traits and cognitive deficits coexist in individuals prone to both drug abuse and violence, suggesting a common origin. Because these excessive and compulsive behaviors have been linked with aberrations in the metabolism and activity of the neurotransmitters dopamine and serotonin, their origins may be partly genetic or biological. Alterations in neurotransmitter function influence activities within the brain's reward center to perturb nervous system arousal levels, thereby increasing stimulation-seeking behaviors. Manifestations of these neurobiological aberrations can be measured in physiological and biochemical processes that serve to mediate these behavioral and psychological outcomes.

Genetic influences in antisocial personality and drug use disorders

While an association between antisocial personality disorder (APD) and substance use disorder (SUD) has been frequently observed, the causes of the comorbidity remain unclear. Adoption and twin studies have found evidence of both genetic and environmental influences in APD and SUD. Therefore, comorbidity between APD and SUD may be the result of shared genetic influences, shared environmental influences, or a combination of the two. However, only a limited number of adoption and twin studies have addressed this issue and the results have not been conclusive. In future studies, a distinction should be made between alcohol and drug abuse and between juvenile and adult APD symptoms. Twin samples of adequate size would allow use of structural equation analytical methods for estimation of the relative magnitude of genetic and environmental influences shared between the two conditions, as well as influences contributing to each specifically. Results would be highly relevant for the clinical setting as well as for efforts to identify the genes involved in either trait.

Indicators of genetic and environmental influences in drug abusing individuals

To assess relative contribution of genetic and environmental influences in individual cases of drug abuse/dependence, separate scales were constructed from DIS (version III) drug symptom items. Using data from 38 MZ and 35 DZ male twin pairs, items with significant MZ/DZ differences in probandwise concordance were assigned to a genetic scale whereas items without significant MZ/DZ differences were assigned to an environmental scale. As expected, significant differences were found between MZ and DZ twins in intraclass correlations for the genetic but not environmental scale. Genetic scores on drug and alcohol scales were correlated (r = 0.40), whereas environmental scales were not. When scores on the genetic scales were compared, the correlation between drug and alcohol scores within individuals was similar to that across MZ twins, both of which were higher than the correlation across DZ twins. These results suggest (1) relative contribution of genetic and environmental influences in individual cases of drug dependence can be assessed, and (2) common genetic mechanisms may be involved in alcohol and drug dependence.