Transdiagnostic risk of mental disorders in offspring of affected parents: a meta-analysis of family high-risk and registry studies

The offspring of parents with mental disorders are at increased risk for developing mental disorders themselves. The risk to offspring may extend transdiagnostically to disorders other than those present in the parents. The literature on this topic is vast but mixed. To inform targeted prevention and genetic counseling, we performed a comprehensive, PRISMA 2020-compliant meta-analysis. We systematically searched the literature published up to September 2022 to retrieve original family high-risk and registry studies reporting on the risk of mental disorders in offspring of parents with any type of mental disorder. We performed random-effects meta-analyses of the relative risk (risk ratio, RR) and absolute risk (lifetime, up to the age at assessment) of mental disorders, defined according to the ICD or DSM. Cumulative incidence by offspring age was determined using meta-analytic Kaplan-Meier curves. We measured heterogeneity with the I2 statistic, and risk of bias with the Quality In Prognosis Studies (QUIPS) tool. Sensitivity analyses addressed the impact of study design (family high-risk vs. registry) and specific vs. transdiagnostic risks. Transdiagnosticity was appraised with the TRANSD criteria. We identified 211 independent studies that reported data on 3,172,115 offspring of parents with psychotic, bipolar, depressive, disruptive, attention-deficit/hyperactivity, anxiety, substance use, eating, obsessive-compulsive, and borderline personality disorders, and 20,428,575 control offspring. The RR and lifetime risk of developing any mental disorder were 3.0 and 55% in offspring of parents with anxiety disorders; 2.6 and 17% in offspring of those with psychosis; 2.1 and 55% in offspring of those with bipolar disorder; 1.9 and 51% in offspring of those with depressive disorders; and 1.5 and 38% in offspring of those with substance use disorders. The offspring's RR and lifetime risk of developing the same mental disorder diagnosed in their parent were 8.4 and 32% for attention-deficit/hyperactivity disorder; 5.8 and 8% for psychosis; 5.1 and 5% for bipolar disorder; 2.8 and 9% for substance use disorders; 2.3 and 14% for depressive disorders; 2.3 and 1% for eating disorders; and 2.2 and 31% for anxiety disorders. There were 37 significant transdiagnostic associations between parental mental disorders and the RR of developing a different mental disorder in the offspring. In offspring of parents with psychosis, bipolar and depressive disorder, the risk of the same disorder onset emerged at 16, 5 and 6 years, and cumulated to 3%, 19% and 24% by age 18; and to 8%, 36% and 46% by age 28. Heterogeneity ranged from 0 to 0.98, and 96% of studies were at high risk of bias. Sensitivity analyses restricted to prospective family high-risk studies confirmed the pattern of findings with similar RR, but with greater absolute risks compared to analyses of all study types. This study demonstrates at a global, meta-analytic level that offspring of affected parents have strongly elevated RR and lifetime risk of developing any mental disorder as well as the same mental disorder diagnosed in the parent. The transdiagnostic risks suggest that offspring of parents with a range of mental disorders should be considered as candidates for targeted primary prevention.

Stigmata that are desired: Contradictions in addiction

Many experts in the etiology, assessment, and treatment of substance use/addiction view stigma and stigmatization - negatively branding addiction and substance users - as obstacles to the solution of the substance misuse problem. Discussions on this topic impact research and policy, and result in oft-repeated calls to remove the stigma from substance use and users. The goal of the article is to analyze the stigmatization concept as applied to substance use/addiction. It is widely accepted in the literature that stigmatization negatively affects substance users because addiction stigma interferes in both seeking and receiving professional care. It is argued that the societal disapproval of substance use/addiction is inappropriate because it is a mental disorder, involving biological processes. Nonetheless, neither those processes nor negative attitudes to substance use affirm the concept of stigmatization as currently applied. This concept conflates potential mistreatment and malpractice with the prosocial justified societal disapproval of a lethally dangerous behavior. Consequently, the stigmatization concept suffers from internal contradictions, is either misleading or redundant, and may do more harm than the supposed mistreatment of substance users that stigmatization connotes. On the contrary, the justified disapproval of harmful behavior may be a factor raising individual resistance to substance use. Instead of mitigating the effects of that disapproval, it may need to be capitalized on. If it is employed explicitly, conscientiously, and professionally, its internalization may be one of the resistance mechanisms needed to achieve any progress in the still elusive prevention of substance use and addiction.

A Gateway That Never Was

This brief communication responds to the article by Rajabi et al., recently published in Behavior Genetics. To test the hypothesis of cigarette smoking as a "gateway" for subsequent opium use and contrast it with the common liability model, Mendelian randomization analysis was applied to data obtained from an Iranian sample, using CHRNA3 rs1051730 as an instrumental variable. It is doubtful, however, if the assumptions of instrumental variable analysis hold in this case. The authors misstate both the gateway hypothesis and the common liability model. The article has many other deficiencies that diminish the veracity of its categorical conclusions that accept the causal interpretation of the "gateway hypothesis" and reject the common liability model, with which the data are fully consistent.

A large-scale genome-wide association study meta-analysis of cannabis use disorder

BACKGROUND

Variation in liability to cannabis use disorder has a strong genetic component (estimated twin and family heritability about 50-70%) and is associated with negative outcomes, including increased risk of psychopathology. The aim of the study was to conduct a large genome-wide association study (GWAS) to identify novel genetic variants associated with cannabis use disorder.

METHODS

To conduct this GWAS meta-analysis of cannabis use disorder and identify associations with genetic loci, we used samples from the Psychiatric Genomics Consortium Substance Use Disorders working group, iPSYCH, and deCODE (20 916 case samples, 363 116 control samples in total), contrasting cannabis use disorder cases with controls. To examine the genetic overlap between cannabis use disorder and 22 traits of interest (chosen because of previously published phenotypic correlations [eg, psychiatric disorders] or hypothesised associations [eg, chronotype] with cannabis use disorder), we used linkage disequilibrium score regression to calculate genetic correlations.

FINDINGS

We identified two genome-wide significant loci: a novel chromosome 7 locus (FOXP2, lead single-nucleotide polymorphism [SNP] rs7783012; odds ratio [OR] 1·11, 95% CI 1·07-1·15, p=1·84 × 10-9) and the previously identified chromosome 8 locus (near CHRNA2 and EPHX2, lead SNP rs4732724; OR 0·89, 95% CI 0·86-0·93, p=6·46 × 10-9). Cannabis use disorder and cannabis use were genetically correlated (rg 0·50, p=1·50 × 10-21), but they showed significantly different genetic correlations with 12 of the 22 traits we tested, suggesting at least partially different genetic underpinnings of cannabis use and cannabis use disorder. Cannabis use disorder was positively genetically correlated with other psychopathology, including ADHD, major depression, and schizophrenia.

INTERPRETATION

These findings support the theory that cannabis use disorder has shared genetic liability with other psychopathology, and there is a distinction between genetic liability to cannabis use and cannabis use disorder.

FUNDING

National Institute of Mental Health; National Institute on Alcohol Abuse and Alcoholism; National Institute on Drug Abuse; Center for Genomics and Personalized Medicine and the Centre for Integrative Sequencing; The European Commission, Horizon 2020; National Institute of Child Health and Human Development; Health Research Council of New Zealand; National Institute on Aging; Wellcome Trust Case Control Consortium; UK Research and Innovation Medical Research Council (UKRI MRC); The Brain & Behavior Research Foundation; National Institute on Deafness and Other Communication Disorders; Substance Abuse and Mental Health Services Administration (SAMHSA); National Institute of Biomedical Imaging and Bioengineering; National Health and Medical Research Council (NHMRC) Australia; Tobacco-Related Disease Research Program of the University of California; Families for Borderline Personality Disorder Research (Beth and Rob Elliott) 2018 NARSAD Young Investigator Grant; The National Child Health Research Foundation (Cure Kids); The Canterbury Medical Research Foundation; The New Zealand Lottery Grants Board; The University of Otago; The Carney Centre for Pharmacogenomics; The James Hume Bequest Fund; National Institutes of Health: Genes, Environment and Health Initiative; National Institutes of Health; National Cancer Institute; The William T Grant Foundation; Australian Research Council; The Virginia Tobacco Settlement Foundation; The VISN 1 and VISN 4 Mental Illness Research, Education, and Clinical Centers of the US Department of Veterans Affairs; The 5th Framework Programme (FP-5) GenomEUtwin Project; The Lundbeck Foundation; NIH-funded Shared Instrumentation Grant S10RR025141; Clinical Translational Sciences Award grants; National Institute of Neurological Disorders and Stroke; National Heart, Lung, and Blood Institute; National Institute of General Medical Sciences.

Discovering weaker genetic associations guided by known associations

Background

The current understanding of the genetic basis of complex human diseases is that they are caused and affected by many common and rare genetic variants. A considerable number of the disease-associated variants have been identified by Genome Wide Association Studies, however, they can explain only a small proportion of heritability. One of the possible reasons for the missing heritability is that many undiscovered disease-causing variants are weakly associated with the disease. This can pose serious challenges to many statistical methods, which seems to be only capable of identifying disease-associated variants with relatively stronger coefficients.

Results

In order to help identify weaker variants, we propose a novel statistical method, Constrained Sparse multi-locus Linear Mixed Model (CS-LMM) that aims to uncover genetic variants of weaker associations by incorporating known associations as a prior knowledge in the model. Moreover, CS-LMM accounts for polygenic effects as well as corrects for complex relatednesses. Our simulation experiments show that CS-LMM outperforms other competing existing methods in various settings when the combinations of MAFs and coefficients reflect different scenarios in complex human diseases.

Conclusions

We also apply our method to the GWAS data of alcoholism and Alzheimer’s disease and exploratively discover several SNPs. Many of these discoveries are supported through literature survey. Furthermore, our association results strengthen the belief in genetic links between alcoholism and Alzheimer’s disease.

Informing Prevention and Intervention Policy Using Genetic Studies of Resistance

The common paradigm for conceptualizing the influence of genetic and environmental factors on a particular disease relies on the concept of risk. Consequently, the bulk of etiologic, including genetic, work focuses on "risk" factors. These factors are aggregated at the high end of the distribution of liability to disease, the latent variable underlying the distribution of probability and severity of a disorder. However, liability has a symmetric but distinct aspect to risk, resistance to disorder. Resistance factors, aggregated at the low end of the liability distribution and supporting health and recovery, appear to be more promising for effective prevention and intervention. Herein, we discuss existing work on resistance factors, highlighting those with known genetic influences. We examine the utility of incorporating resistance genetics in prevention and intervention trials and compare the statistical power of a series of ascertainment schemes to develop a general framework for examining resistance outcomes in genetically informative designs. We find that an approach that samples individuals discordant on measured liability, a low-risk design, is the most feasible design and yields power equivalent to or higher than commonly used designs for detecting resistance genetic and environmental effects.

Transancestral GWAS of alcohol dependence reveals common genetic underpinnings with psychiatric disorders

Liability to alcohol dependence (AD) is heritable, but little is known about its complex polygenic architecture or its genetic relationship with other disorders. To discover loci associated with AD and characterize the relationship between AD and other psychiatric and behavioral outcomes, we carried out the largest genome-wide association study to date of DSM-IV-diagnosed AD. Genome-wide data on 14,904 individuals with AD and 37,944 controls from 28 case-control and family-based studies were meta-analyzed, stratified by genetic ancestry (European, n = 46,568; African, n = 6,280). Independent, genome-wide significant effects of different ADH1B variants were identified in European (rs1229984; P = 9.8 × 10-13) and African ancestries (rs2066702; P = 2.2 × 10-9). Significant genetic correlations were observed with 17 phenotypes, including schizophrenia, attention deficit-hyperactivity disorder, depression, and use of cigarettes and cannabis. The genetic underpinnings of AD only partially overlap with those for alcohol consumption, underscoring the genetic distinction between pathological and nonpathological drinking behaviors.

Variants on chromosome 4q21 near PKD2 and SIBLINGs are associated with dental caries

A recent genome-wide association study for dental caries nominated the chromosomal region 4q21 near ABCG2, PKD2 and the SIBLING gene family. In this investigation we followed-up and fine-mapped this region using a tag-SNP (single nucleotide polymorphism) approach in 13 age- and race-stratified samples from 6 independent studies (N=4,089). Participants were assessed for dental caries via intra-oral examination and 49 tag-SNPs were genotyped capturing much of the variation in the 4q21 locus. Linear models were used to test for genetic association, while adjusting for sex, age, and components of ancestry. SNPs in and near PKD2 showed significant evidence of association in individual samples of black adults (rs17013735, p-value=0.0009) and white adults (rs11938025; p-value=0.0005; rs2725270, p-value=0.003). Meta-analyses across black adult samples recapitulated the association with rs17013735 (p-value=0.003), which occurs at low frequency in non-African populations, possibly explaining the race-specificity of the effect. In addition to race-specific associations, we also observed evidence of gene-by-fluoride exposure interaction effects in white adults for SNP rs2725233 upstream of PKD2 (p=0.002). Our results show evidence of regional replication, though no single variant clearly accounted for the original GWAS signal. Therefore, while we interpret our results as strengthening the hypothesis that chromosome 4q21 may impact dental caries, additional work is needed.

Risk and resistance perspectives in translation-oriented etiology research

Risk for a disorder and the mechanisms that determine its elevation, risk factors, are the focus of medical research. Targeting risk factors should serve the goal of prevention and treatment intervention. Risk, however, is but one of the aspects of liability to a disorder, a latent trait that encompasses effects of all factors leading to or from the diagnostic threshold. The coequal but opposite aspect of liability is resistance to a disorder. The factors that increase resistance and thus enable prevention or recovery may differ from those that elevate risk. Accordingly, there are nontrivial differences between research perspectives that focus on risk and on resistance. This article shows how this distinction translates into goals and methods of research and practice, from the choice of potential mechanisms tested to the results sought in intervention. The resistance concept also differs from those of "resilience" and "protective factors," subsuming but not limited to them. The implications of the concept are discussed using substance use disorder as an example and substantiate the need for biomedical research and its translation to shift to the resistance perspective.

Item Response Theory Analysis to Assess Dimensionality of Substance Use Disorder Abuse and Dependence Symptoms

BACKGROUND

Item response theory (IRT) based studies conducted on diverse samples showed a single dominant factor for DSM-III-R and DSM-IV substance use disorder (SUD) abuse and dependence symptoms of alcohol, cannabis, sedative, cocaine, stimulants, and opiates use disorders. IRT provides the opportunity, within a person-centered framework, to accurately gauge each person's severity of disorder that, in turn, informs required intensiveness of treatment.

OBJECTIVES

The aim of this study was to determine whether the SUD symptoms indicate a unidimensional trait or instead need to be conceptualized and quantified as a multidimensional scale.

METHODS

The sample was composed of families of adult SUD+ men (n=349), and SUD+ women (n=173), who qualified for DSM-III-R diagnosis of substance use disorder (abuse or dependence) and families of adult men and women who did not qualify for a SUD diagnosis (SUD- men: n=190, SUD- women: n=133). An expanded version of the Structured Clinical Interview for DSM-III-R (SCID) was administered to characterize lifetime and current substance use disorders. Item response theory methodology was used to assess the dimensionality of DSM-III-R SUD abuse and dependence symptoms.

RESULTS

A bi-factor model provided the optimal representation of the factor structure of SUD symptoms in males and females. SUD symptoms are scalable as indicators of a single common factor, corresponding to general (non-drug-specific, common) liability to addiction, combined with drug-specific liabilities.

CONCLUSIONS

IRT methodology used to quantify the continuous general liability to addiction (GLA) latent trait in individuals having SUD symptoms was found effective for accurately measuring SUD severity in men and women. This may be helpful for person-centered medicine approaches to effectively address intensity of treatment.

Effects of enamel matrix genes on dental caries are moderated by fluoride exposures

Dental caries (tooth decay) is the most common chronic disease, worldwide, affecting most children and adults. Though dental caries is highly heritable, few caries-related genes have been discovered. We investigated whether 18 genetic variants in the group of non-amelogenin enamel matrix genes (AMBN, ENAM, TUFT1, and TFIP11) were associated with dental caries experience in 13 age- and race-stratified samples from six parent studies (N = 3,600). Linear regression was used to model genetic associations and test gene-by-fluoride interaction effects for two sources of fluoride: daily tooth brushing and home water fluoride concentration. Meta-analysis was used to combine results across five child and eight adult samples. We observed the statistically significant association of rs2337359 upstream of TUFT1 with dental caries experience via meta-analysis across adult samples (p < 0.002) and the suggestive association for multiple variants in TFIP11 across child samples (p < 0.05). Moreover, we discovered two genetic variants (rs2337359 upstream of TUFT1 and missense rs7439186 in AMBN) involved in gene-by-fluoride interactions. For each interaction, participants with the risk allele/genotype exhibited greater dental caries experience only if they were not exposed to the source of fluoride. Altogether, these results confirm that variation in enamel matrix genes contributes to individual differences in dental caries liability, and demonstrate that the effects of these genes may be moderated by protective fluoride exposures. In short, genes may exert greater influence on dental caries in unprotected environments, or equivalently, the protective effects of fluoride may obviate the effects of genetic risk alleles.

Genetic Association of MPPED2 and ACTN2 with Dental Caries

The first genome-wide association study of dental caries focused on primary teeth in children aged 3 to 12 yr and nominated several novel genes: ACTN2, EDARADD, EPHA7, LPO, MPPED2, MTR, and ZMPSTE24. Here we interrogated 156 single-nucleotide polymorphisms (SNPs) within these candidate genes for evidence of association with dental caries experience in 13 race- and age-stratified samples from 6 independent studies (n = 3600). Analysis was performed separately for each sample, and results were combined across samples via meta-analysis. MPPED2 was significantly associated with caries via meta-analysis across the 5 childhood samples, with 4 SNPs showing significant associations after gene-wise adjustment for multiple comparisons (p < .0026). These results corroborate the previous genome-wide association study, although the functional role of MPPED2 in caries etiology remains unknown. ACTN2 also showed significant association via meta-analysis across childhood samples (p = .0014). Moreover, in adults, genetic association was observed for ACTN2 SNPs in individual samples (p < .0025), but no single SNP was significant via meta-analysis across all 8 adult samples. Given its compelling biological role in organizing ameloblasts during amelogenesis, this study strengthens the hypothesis that ACTN2 influences caries risk. Results for the other candidate genes neither proved nor precluded their associations with dental caries.

High and low neurobehavior disinhibition clusters within locales: implications for community efforts to prevent substance use disorder

BACKGROUND

Knowledge of where substance use and other such behavioral problems frequently occur has aided policing, public health, and urban planning strategies to reduce such behaviors. Identifying locales characterized by high childhood neurobehavioral disinhibition (ND), a strong predictor of substance use and consequent disorder (SUD), may likewise improve prevention efforts.

OBJECTIVES

The distribution of ND in 10-12-year olds was mapped to metropolitan Pittsburgh, PA, and tested for clustering within locales.

METHODS

The 738 participating families represented the population in terms of economic status, race, and population distribution. ND was measured using indicators of executive cognitive function, emotion regulation, and behavior control. Innovative geospatial analyzes statistically tested clustering of ND within locales while accounting for geographic barriers (large rivers, major highways), parental SUD severity, and neighborhood quality.

RESULTS

Clustering of youth with high and low ND occurred in specific locales. Accounting for geographic barriers better delineated where high ND is concentrated, areas which also tended to be characterized by greater parental SUD severity and poorer neighborhood quality.

CONCLUSIONS AND SIGNIFICANCE

Offering programs that have been demonstrated to improve inhibitory control in locales where youth have high ND on average may reduce youth risk for SUD and other problem behaviors. As demonstrated by the present results, geospatial analysis of youth risk factors, frequently used in community coalition strategies, may be improved with greater statistical and measurement rigor.

Longitudinal associations from neurobehavioral disinhibition to adolescent risky sexual behavior in boys: direct and mediated effects through moderate alcohol consumption

PURPOSE

This longitudinal study tested the hypothesis that neurobehavioral disinhibition (ND) in childhood, mediated by alcohol use, portends risky sexual behavior (number of sexual partners) in midadolescence.

METHODS

Participants were 410 adolescent boys. Neurobehavioral disinhibition was assessed at 11.3 years of age. Frequency and quantity of alcohol use on a typical drinking occasion were assessed at 13.4 years of age at first follow-up, and sexual behavior at 16.0 years at second follow-up.

RESULTS

Quantity of alcohol consumed on a typical drinking occasion, but not frequency of alcohol use, mediated the relation between ND and number of sexual partners.

CONCLUSIONS

These findings indicate that number of sexual partners in midadolescence is predicted by individual differences in boys' psychological self-regulation during childhood and moderate alcohol consumption in early adolescence, and that ND may be a potential target for multi-outcome public health interventions.

Common liability to addiction and "gateway hypothesis": theoretical, empirical and evolutionary perspective

BACKGROUND

Two competing concepts address the development of involvement with psychoactive substances: the "gateway hypothesis" (GH) and common liability to addiction (CLA).

METHOD

The literature on theoretical foundations and empirical findings related to both concepts is reviewed.

RESULTS

The data suggest that drug use initiation sequencing, the core GH element, is variable and opportunistic rather than uniform and developmentally deterministic. The association between risks for use of different substances, if any, can be more readily explained by common underpinnings than by specific staging. In contrast, the CLA concept is grounded in genetic theory and supported by data identifying common sources of variation in the risk for specific addictions. This commonality has identifiable neurobiological substrate and plausible evolutionary explanations.

CONCLUSIONS

Whereas the "gateway" hypothesis does not specify mechanistic connections between "stages", and does not extend to the risks for addictions, the concept of common liability to addictions incorporates sequencing of drug use initiation as well as extends to related addictions and their severity, provides a parsimonious explanation of substance use and addiction co-occurrence, and establishes a theoretical and empirical foundation to research in etiology, quantitative risk and severity measurement, as well as targeted non-drug-specific prevention and early intervention.

The AVPR1A gene and substance use disorders: association, replication, and functional evidence

BACKGROUND

The liability to addiction has been shown to be highly genetically correlated across drug classes, suggesting nondrug-specific mechanisms.

METHODS

In 757 subjects, we performed association analysis between 1536 single nucleotide polymorphisms (SNPs) in 106 candidate genes and a drug use disorder diagnosis (DUD).

RESULTS

Associations (p ≤ .0008) were detected with three SNPs in the arginine vasopressin 1A receptor gene, AVPR1A, with a gene-wise p value of 3 × 10(-5). Bioinformatic evidence points to a role for rs11174811 (microRNA binding site disruption) in AVPR1A function. Based on literature implicating AVPR1A in social bonding, we tested spousal satisfaction as a mediator of the association of rs11174811 with the DUD. Spousal satisfaction was significantly associated with DUD in males (p < .0001). The functional AVPR1A SNP, rs11174811, was associated with spousal satisfaction in males (p = .007). Spousal satisfaction was a significant mediator of the relationship between rs11174811 and DUD. We also present replication of the association in males between rs11174811 and substance use in one clinically ascertained (n = 1399) and one epidemiologic sample (n = 2231). The direction of the association is consistent across the clinically-ascertained samples but reversed in the epidemiologic sample. Lastly, we found a significant impact of rs11174811 genotype on AVPR1A expression in a postmortem brain sample.

CONCLUSIONS

The findings of this study call for expansion of research into the role of the arginine vasopressin and other neuropeptide system variation in DUD liability.

Measurement of the risk for substance use disorders: phenotypic and genetic analysis of an index of common liability

The inability to quantify the risk for disorders, such as substance use disorders (SUD), hinders etiology research and development of targeted intervention. Based on the concept of common transmissible liability to SUD related to illicit drugs, a method enabling quantification of this latent trait has been developed, utilizing high-risk design and item response theory. This study examined properties of a SUD transmissible liability index (TLI) derived using this method. Sons of males with or without SUD were studied longitudinally from preadolescence to young adulthood. The properties of TLI, including its psychometric characteristics, longitudinal risk assessment and ethnic variation, were examined. A pilot twin study was conducted to analyze the composition of TLI's phenotypic variance. The data suggest that TLI has concurrent, incremental, predictive and discriminant validity, as well as ethnic differences. The data suggest a high heritability of the index in males. The results suggest applicability of the method for genetic and other etiology-related research, and for evaluation of individual risk.

Dopamine receptors in human lymphocytes: radioligand binding and quantitative RT-PCR assays

Analysis of dopamine receptors (DR) in lymphocytes of the human peripheral blood mononuclear cell (PBMC) fraction is an attractive tool for evaluation of functional properties of dopaminergic function underlying variation in complex psychological/psychopathological traits. Receptor binding assays (RBAs) with selective radioligands, which are widely used in CNS studies, have not produced consistent results when applied to isolated PBMC. We tested the assay conditions that could be essential for detection of DR in human PBMC and their membrane preparations. Using [(3)H]SCH23390, a dopamine D1-like receptor antagonist, we demonstrated the presence of two binding sites in PBMC-derived membrane fraction. One of them is characterized by the K(d) value consistent with that reported for D5 dopamine receptors in human lymphocytes, whereas the other K(d) value possibly corresponds to serotonin receptor(s). Although D5 receptor binding sites in PBMC membranes could be characterized by binding assays, the low protein expression and the large volume of blood needed for membrane preparation render the binding method impracticable for individual phenotyping. In contrast, real-time RT-PCR may be used for this purpose, contingent on the relationship between DR expression in the brain and in lymphocytes. The expression of the DRD2-DRD5 genes, as detected by this method, varied widely among samples, whereas the DRD1 expression was not detected. The expression levels were comparable with those in the brain for DRD3 and DRD4, and were significantly lower for DRD2 and DRD5.

Physical maturation, peer environment, and the ontogenesis of substance use disorders

The risk for substance use disorders (SUD) is transmissible between generations via both genetic and environmental mechanisms. One path that is hypothesized to mediate this transmission and include both types of mechanisms is through faster physiological maturation, leading to suboptimal self-regulation, affiliation with deviant peers, and higher risk for conduct disorder (CD). Extending prior research, this hypothesis was tested in a longitudinal study. A sample of 478 males whose fathers were affected with SUD or psychiatrically normal was assessed prospectively at ages from 9-13 to 17-20. The DSM-III-R diagnoses were obtained using standard methodology. Blood testosterone was assayed by radioimmunoassay, and Tanner staging was used to evaluate sexual maturation. Peer deviance was evaluated by the Peer Delinquency Scale. Correlation and path analysis, Cox proportional hazard regression, and growth curve modeling were used to determine the relationships between the variables. The data support the hypothesis that parental SUD liability influences the rate of physiological maturation in offspring, which in turn is related to affiliation with deviant peers and an elevated rate of the development of CD and SUD.

Pittsburgh Registry of Infant Multiplets (PRIM): An Update

This article is an updated review of the Pittsburgh Registry of Infant Multiplets including recruitment methods, data collection, and results of pilot studies conducted in this registry. The main goal of the registry is to study psychological development. The risk for behavior disorders including substance use disorders, as well as language development and dental health are among research targets. Pilot data on the heritability of minor physical anomalies and neuropsychological characteristics (Continuous Performance Test) are reported.

Pittsburgh Registry of Infant Multiplets (PRIM): an update

This article is an updated review of the Pittsburgh Registry of Infant Multiplets including recruitment methods, data collection, and results of pilot studies conducted in this registry. The main goal of the registry is to study psychological development. The risk for behavior disorders including substance use disorders, as well as language development and dental health are among research targets. Pilot data on the heritability of minor physical anomalies and neuropsychological characteristics (Continuous Performance Test) are reported.

Haplotypes of the monoamine oxidase genes and the risk for substance use disorders

Monoamine oxidase A (MAOA) locus is an attractive candidate for exploring genetic contribution to the variation in the risk for substance use disorders (SUD) because of its important role in the metabolism of neurotransmitters, including dopamine and serotonin. Prior findings have suggested an association of the MAOA gene with the risk for early onset SUD. To extend this research, we genotyped four MAOA markers (two VNTR polymorphisms and two SNPs) and built a cladogram reflecting the evolutionary history of MAOA haplotypes [Nguyen et al., under review]. The cladogram served as the framework for nested ANOVA and logit analyses of association between MAOA and indices of liability to SUD (diagnosis, age of onset, and a dimensional index of substance use related problems) in a sample of adult males of European ancestry. Whereas no association was found for the categorical diagnosis, a significant relationship was detected between the dimensional liability indices and MAOA haplotypes. Overall, our results, albeit not definitive, are consistent with the hypothesis that variants in MAOA account for a small portion of the variance of SUD risk, possibly mediated by liability to early onset behavioral problems.

Liability to substance use disorders: 1. Common mechanisms and manifestations

Variation in the risk for and severity of substance use disorders (SUD) in the population is caused by multiple organismic (genetic, biochemical, psychological) and environmental factors. Whereas drug- or drug-class-specific liability mechanisms exist, a substantial proportion of variance in the risk is shared between specific liabilities, reflecting mechanisms that determine common liability to SUD. Data from epidemiologic, clinical, psychological, physiological, biochemical, and family and genetic studies reviewed in this paper indicate the existence of mechanisms and characteristics shared in common by liabilities to SUD related to different drugs. These mechanisms can be conceptualized as common liability to SUD, a latent trait accounting for a substantial portion of variation in SUD risk and severity and determined by all factors influencing the probability of SUD development. An accompanying paper describes an approach to the quantitative estimation of this trait.

Liability to substance use disorders: 2. A measurement approach

Liabilities to complex disorders, discussed in the accompanying paper, present difficulties in measurement related to the arbitrariness of diagnostic threshold definitions and problems with discrimination between trait values, especially within the 'normal' individuals. The inability to quantitatively estimate the risk for a disorder, such as substance use disorders (SUD), is an obstacle for studying etiological (e.g. genetic) mechanisms and developing efficient prevention and treatment measures. Based on the concept of common liability to SUD, this paper delineates an application of the longitudinal family/high-risk design and item response theory to the development of a continuous index of liability. The method has been tested in both simulation study and empirical data. The approach described affords the opportunity to quantitatively estimate the risk for SUD at an early age and before any drug exposure. This method is also applicable to measuring liabilities to other complex disorders, especially those with relatively late onset.

Dopamine system genes and attention deficit hyperactivity disorder: a meta-analysis

The dopamine system may play a major role in the development of attention deficit hyperactivity disorder (ADHD). We applied a random-effects model meta-analysis to family-based studies of association between ADHD and the dopamine system genes DRD4, DRD5 and DAT1. A statistical test of heterogeneity was conducted for each group of studies. The meta-analysis of DRD4 included data from 13 studies, with a total of 571 informative meioses. The pooled odds ratio estimate was 1.41 (95% CI 1.20-1.64, =1.57 x 10 ), demonstrating positive association. For DRD5, data from five studies, with a total of 340 informative meioses, were combined yielding a pooled odds ratio of 1.57 (95% CI 1.25-1.96, =8.28 x 10 ). Eleven studies examining DAT1, with a total of 824 informative meioses, yielded a non-significant pooled odds ratio estimate of 1.27 (95% CI 0.99-1.63, 0.06). There was no support of heterogeneity between the studies. Overall, the meta-analyses support the involvement of the dopamine system genes in ADHD liability variation and suggest the need for studies examining interactions between these genes.

Does adverse family environment or sex matter in the salivary cortisol responses to anticipatory stress?

We previously reported that in anticipation of a modest stressor, preadolescent sons of drug-dependent fathers (HR) demonstrated a diminished salivary cortisol response relative to comparison boys. No data were available concerning anticipatory salivary cortisol responses in preadolescent daughters of HR fathers. Additionally, we hypothesized that diminished stress responses in HR youth might be an adaptation to a stressful family environment. Consequently, in this report we have examined the role of family environment in the anticipatory salivary cortisol responses in both HR boys and girls as well as their association with a measure of distress in the family environment. Independent of sex, HR children had diminished anticipatory cortisol responses. Girls had significantly higher salivary cortisol concentrations, pre- and post-stressor. However, contrary to our expectation, we could not demonstrate an association between salivary cortisol responses and the measures of the family environment. These results suggest that there may be a sex difference in salivary cortisol dynamics in preadolescent children; however, the functional status of the current family environment does not appear to be related to cortisol reactivity.

Quantitative trait linkage analysis of the liability underlying a common oligogenic disease

We utilized pedigree discriminant and factor analytic approaches to combine multivariate phenotypic information into a single liability phenotype in the isolate and general populations. We applied two-stage relative-pair quantitative trait linkage analysis to detect genetic contributions to variation in the resulting liability phenotypes. Linkage analysis revealed several regions of suggestive linkage in both the general and isolate populations, the majority of which appear in retrospect to be false positives. A likely explanation is an overall lack of power given that we tested hypotheses in data from only one replicate. However, it may be possible that a construct that ignores affection status when using liability-associated characteristics as indicators of this construct is not the most effective approach in modeling the liability underlying a complex phenotype.

Preadolescent children of substance-dependent fathers with antisocial personality disorder: psychiatric disorders and problem behaviors

We compared psychiatric disorders and problem behavior scores in pre-adolescent children of fathers with alcohol or other drug dependence and ASP (SD+/ASP+), children whose fathers had substance dependence without ASP (SD+/ASP-), and children whose fathers were without either disorder (SD-/ASP-). SD+/ASP+ children showed elevated rates of major depression, conduct disorder, attention deficit hyperactivity disorder, oppositional defiant disorder, and separation anxiety disorder when compared to SD+/ASP- and SD-/ASP- children. SD+/ASP+ children had higher internalizing and externalizing problem behavior scores than the other two groups of children. The results suggest that SD+/ASP+ children are at significant risk for internalizing and externalizing psychopathology.

Developmental sources of variation in liability to adolescent substance use disorders

This review provides a synthesis of the literature on the complex sequence of maturational, psychosocial, and neuroadaptive processes that lead to substance use disorders (SUD) in adolescence. A brief overview introduces the concepts of liability to SUD and epigenesis. A theory is presented explaining how affective, cognitive, and behavioral dysregulation in late childhood is exacerbated during early and middle adolescence by family and peer factors, as well as puberty, leading to substance use. Continued exacerbation of the three components of dysregulation by drug and non-drug stressors during late adolescence is posited to result in neuroadaptations that increase the likelihood of developing SUD, particularly in high-risk individuals. Implications for etiologic research as well as clinical and preventive interventions are discussed.

Antisociality, substance dependence, and the DRD5 gene: a preliminary study

A pilot population-based study of a microsatellite polymorphism at the DRD5 locus in adult European-Americans showed its association with childhood symptom counts for oppositional defiant disorder (ODD) in males and females and adult antisocial personality disorder (ASPD) in females. No association with childhood conduct disorder symptom count was observed. ODD mediated the genotype-ASPD relationship in females. Neither ODD nor ASPD significantly mediated the relationship between the genotype and the liability to substance dependence (SD). The data suggest involvement of the DRD5 locus in the variation and sexual dimorphism of SD liability and antisociality and in the developmental continuity of antisociality.

Genetic studies of substance abuse

Genetic studies of substance abuse indicate that variation in the risk for the disorder in the population is contributed by differences in both individual genotypes and environment. Recent developments in genetics raise the possibility of disentangling the complex system of genotype-environment interaction that determines the development of the individual behavioral phenotype. This paper reviews the concepts, methods and results pertaining to genetic investigation of substance abuse.

Segregation analysis of attention deficit hyperactivity disorder

We performed segregation analysis on 495 nuclear families, ascertained for the father's substance abuse diagnosis, in an attempt to determine the role of genetic and other influences in determining the variability of DSM-III-R-defined attention deficit hyperactivity disorder (ADHD). For our analyses, ADHD was treated as a quantitative variable, utilizing the semicontinuous scale provided by the 15-item symptom count within DSM-III-R. Analyses consisted of both class A and class D regressive models for which covariate effects (socioeconomic status) and sex dependence were estimated. Segregation analysis of the quantitative trait (ADHD symptom count) in the entire data set supported a transmissible non-Mendelian major effect. Models which were sex-dependent and included covariate effects provided the best fit to the data. In addition, similar analyses were performed on a 130-nuclear family subgroup of the data set in which at least one of the members of the nuclear family met DSM-III-R diagnostic criteria for ADHD. The sex-dependent Mendelian codominant model was best supported by the data, while other models could be rejected. Incorporating covariate effects did not provide a better fit for the data. Thus, this study is consistent with Mendelian transmission of ADHD symptom count in a clinically relevant population. Overall, our results support the presence of a heritable continuous trait of which ADHD represents an extreme.

An association between a microsatellite polymorphism at the DRD5 gene and the liability to substance abuse: pilot study

We have conducted a population-based association study of substance abuse and a microsatellite at the dopamine D5 receptor locus (DRD5) in a sample of European-American males and females with substance dependence (SA) or without any psychiatric disorder. Overrepresentation of the most frequent allele (148 bp) was found in males in the SA group (OR = 2.2, P = .02); this finding was reproduced in females (OR = 5.4, p < .001). The difference in the frequencies of this allele between SA males and SA females was statistically significant. The genotype coded in accordance with the dose of this allele correlated with substance abuse liability in males and females (stronger in females) and with novelty seeking in females. There was no evidence of correlation between the genotypes of spouses that could be induced by assortative mating for the liability to substance abuse. The data suggest that the DRD5 locus is involved in the variation and sex dimorphism of substance abuse liability.

Mating assortment and the liability to substance abuse

Assortative mating can exert a profound influence on the phenotypic composition of the population since it may result in an increase in the frequency of the genotypes associated with extreme phenotypes. Applied to the risk for a disorder such as substance abuse, this would mean a possibility for an increase in the risk and severity of the disorder in consecutive generations. This paper reviews the theoretical and empirical literature on mechanisms related to mate resemblance for the liability to substance abuse, sources and consequences of such resemblance, and suggests directions for further research.

A dinucleotide repeat polymorphism at the gene for monoamine oxidase A and measures of aggressiveness

The relationship between measures of aggressiveness (personality questionnaire scales, conduct disorder diagnosis, and symptom count) and a recently discovered dinucleotide repeat length polymorphism at the monoamine oxidase type A (MAOA) gene (MAOCA-1) as a candidate locus was examined in adolescents using polymerase chain reaction. No significant correlation between aggression scales and repeat length at the MAOCA-1 marker was found, whereas the categorical diagnosis of conduct disorder showed a nonsignificant trend for an association with the marker. Alternative explanations of this trend are discussed. The data obtained suggest that the polymorphism studied is not associated with the variation in aggressiveness.

Salivary cortisol responses and the risk for substance abuse in prepubertal boys

Investigations of adults with a psychoactive substance use disorder (PSUD) or antisocial behavior have reported diminished secretion of the adrenal "stress" hormone, cortisol. Consequently, we determined whether prepubertal sons of PSUD fathers, at high risk for later PSUD, differed from controls on salivary cortisol concentrations before, and after, an anticipated stressor. The roles of problematic behavioral disposition and state anxiety in the cortisol responses were also examined. A significant risk-group x time interaction for salivary cortisol concentrations was found, with high-risk boys secreting less salivary cortisol than controls when anticipating the task. High-risk boys also had significantly higher scores for aggressive delinquency and impulsivity that wholly accounted for the risk-group x time effect on salivary cortisol. Thus, cortisol hyporesponsivity was associated with the dysregulated behaviors prevalent among high-risk boys. The results suggest that cortisol hyporesponsivity could be a "marker" for later antisociality and PSUD.

Preliminary evidence for an association of a dinucleotide repeat polymorphism at the MAOA gene with early onset alcoholism/substance abuse

An association between the liability to early onset alcoholism/substance abuse and a recently discovered dinucleotide repeat length polymorphism at the MAOA gene (MAOCA-1) was examined using polymerase chain reaction (PCR). A significant correlation between the presence/absence of the disorder and the length of the MAOCA-1 repeat was found in males, but not females, with "long" alleles (repeat length above 115 bp) associated with both increased risk for the disorder and lower age of onset of substance abuse. These preliminary data suggest that further exploration of the relationship between the MAOA gene and behavioral traits in an expanded sample is warranted.

Aggressivity, inattention, hyperactivity, and impulsivity in boys at high and low risk for substance abuse

Aggressivity, inattention, hyperactivity, and impulsivity are cardinal dimensions of externalizing behavior problems of childhood. They are diagnostic and clinical features of childhood disorders, and are thought to be linked to the subsequent development of adult disorders such as substance abuse (SA). Little is known, however, about the convergent and discriminant validity of these four constructs. We used multiple measures to develop indices of aggressivity, inattention, hyperactivity, and impulsivity in a sample of 10- to 12-year-old boys (N = 183) with and without a family history of SA. Data were taken from mother reports, child reports, teacher reports, and laboratory tasks. The study aims were (1) to test the convergent and discriminant validity of aggressivity, inattention, hyperactivity, and impulsivity; (2) to examine whether the data were consistent with a model specifying the four constructs as indicators of one superordinate factor; and (3) to differentiate boys with and without a family history of SA in construct scores. The results supported the convergent and discriminant validity of the four constructs. Although discriminable, the constructs covaried strongly and were consistent with a model specifying them as indicators of a single superordinate factor. Boys with a family history of substance abuse scored higher than control boys on aggressivity, inattention, and impulsivity scores, but the groups did not differ on hyperactivity scores. The results are discussed in terms of the role of childhood behavior problems in vulnerability to SA.

Antisocial symptoms in preadolescent boys and in their parents: associations with cortisol

Conduct disorder (CD) symptom counts in preadolescent boys, and antisocial personality disorder (ASP) and childhood conduct disorder symptom counts in their parents, were used as dimensional measures of behavioral deviation. A significant correlation was found for CD and ASP symptom counts between the two parents and between CD symptom counts of the children and parental CD and ASP symptom counts. Although socioeconomic level correlated negatively with parental symptom counts, no association was observed between parental socioeconomic status and children's CD symptom counts. Saliva cortisol level in the children was negatively associated with their CD symptom count and with their fathers' ASP count. Cortisol level was also lower among sons whose fathers had CD as children and subsequently developed ASP compared with the cortisol level in sons whose fathers either did not have any Axis I psychiatric disorder or did not develop ASP.

A genetic study of alcoholism in the Moscow population: preliminary findings

This article reports the preliminary results of a family study of alcoholism in the Moscow population. A comparison of male and female alcoholic inpatients revealed differences between them in the patterns of alcoholism development and in the frequencies of the disorder among male and female probands' parents and siblings. Those differences, particularly those observed in the fathers of the female and male probands, may suggest that the liability and genetic predisposition to alcoholism in female alcoholics, on the average, are higher than those in male alcoholics. There were also differences between male and female probands in the frequencies of the types of drinking behavior (including alcoholism) we used to characterize individual phenotypes as to the liability to alcoholism in the probands' parents and spouses, indicating that the higher the liability and/or genetic predisposition to alcoholism the higher the probability of the proband's marriage to an individual with a higher liability to the disorder. The data on the comparison of the probands' children with their parents affectedness imply the possibility of a relationship between the genetic predisposition to alcoholism and the risk for mental and somatic disturbances in offspring of alcoholics.

The psychiatric diagnosis of alcoholism: critique and proposed reformulation

A taxonomy of alcohol problem involvement is proposed which encompasses categorical and dimensional approaches to classification. It is argued that contemporary nosology such as that described in DSM or ICD cannot, in principle, yield discrete categories containing homogeneous membership. Nor does current classification and diagnosis yield sufficient specific information necessary for effective treatment. These limitations are not resolvable by additional empirical research; rather, as discussed herein, a new conceptual framework and focus are required. The proposed new taxonomy comprises the first step in developing a comprehensive and clinically useful method for characterizing the alcohol consuming population.