Strong and weak cross-inheritance of substance use disorders in a nationally representative sample.

Substance use disorders (SUDs) are moderately to highly heritable and are in part cross-transmitted genetically, as observed in twin and family studies. We performed exome-focused genotyping to examine the cross-transmission of four SUDs: alcohol use disorder (AUD, n = 4487); nicotine use disorder (NUD, n = 4394); cannabis use disorder (CUD, n = 954); and nonmedical prescription opioid use disorder (NMPOUD, n = 346) within a large nationally representative sample (n = 36,309), the National Epidemiologic Survey on Alcohol and Related Conditions-III (NESARC-III). All diagnoses were based on in-person structured psychiatric interview (AUDADIS-5). SUD cases were compared alone and together to 3959 "super controls" who had neither a SUD nor a psychiatric disorder using an exome-focused array assaying 363,496 SNPs, yielding a representative view of within-disorder and cross-disorder genetic influences on SUDs. The 29 top susceptibility genes for one or more SUDs overlapped highly with genes previously implicated by GWAS of SUD. Polygenic scores (PGS) were computed within the European ancestry (EA) component of the sample (n = 12,505) using summary statistics from each of four clinically distinct SUDs compared to the 3959 "super controls" but then used for two distinctly different purposes: to predict SUD severity (mild, moderate, or severe) and to predict each of the other 3 SUDs. Our findings based on PGS highlight shared and unshared genetic contributions to the pathogenesis of SUDs, confirming the strong cross-inheritance of AUD and NUD as well as the distinctiveness of inheritance of opioid use disorder.

Leptin Gene and Leptin Receptor Gene Polymorphisms in Alcohol Use Disorder: Findings Related to Psychopathology.

Comorbidity between alcohol use disorder (AUD) and other addictive and psychiatric disorders is highly prevalent and disabling; however, the underlying biological correlates are not fully understood. Leptin is a peptide hormone known for its role in energy homeostasis and food intake. Furthermore, leptin plays a key role in the activity of the hypothalamic-pituitary-adrenal (HPA) axis and of several neurotransmitter systems that regulate emotionality and behavior. However, human studies that have investigated circulating leptin levels in relation to AUD and affective disorders, such as anxiety and depression, are conflicting. Genetic-based analyses of the leptin gene (LEP) and leptin receptor gene (LEPR) have the potential of providing more insight into the potential role of the leptin system in AUD and comorbid psychopathology. The aim of the current study was to investigate whether genotypic variations at LEP and LEPR are associated with measures of alcohol use, nicotine use, anxiety, and depression, all of which represent common comorbidities with AUD. Haplotype association analyses were performed, using data from participants enrolled in screening and natural history protocols at the National Institute on Alcohol Abuse and Alcoholism (NIAAA). Analyses were performed separately in European Americans and African Americans due to the variation in haplotype diversity for most genes between these groups. In the European American group, one LEP haplotype (EB2H4) was associated with lower odds of having a current AUD diagnosis, two LEPR haplotypes (EB7H3, EB8H3) were associated with lower cigarette pack years and two LEPR haplotypes (EB7H2, EB8H2) were associated with higher State-Trait Anxiety Inventory (STAI-T) scores. In the African American group, one LEP haplotype (AB2H8) was associated with higher cigarette pack years and one LEP haplotype (AB3H2) was associated with lower Fagerström Test for Nicotine Dependence (FTND) scores. Overall, this study found that variations in the leptin and leptin receptor genes are associated with measures of alcohol use, nicotine use, and anxiety. While this preliminary study adds support for a role of the leptin system in AUD and psychopathologies, additional studies are required to fully understand the underlying mechanisms and potential therapeutic implications of these findings.

Epigenome-wide association study and multi-tissue replication of individuals with alcohol use disorder: evidence for abnormal glucocorticoid signaling pathway gene regulation.

Alcohol use disorder (AUD) is a chronic debilitating disorder with limited treatment options and poorly defined pathophysiology. There are substantial genetic and epigenetic components; however, the underlying mechanisms contributing to AUD remain largely unknown. We conducted the largest DNA methylation epigenome-wide association study (EWAS) analyses currently available for AUD (total N = 625) and employed a top hit replication (N = 4798) using a cross-tissue/cross-phenotypic approach with the goal of identifying novel epigenetic targets relevant to AUD. Results show that a network of differentially methylated regions in glucocorticoid signaling and inflammation-related genes were associated with alcohol use behaviors. A top probe consistently associated across all cohorts was located in the long non-coding RNA growth arrest specific five gene (GAS5) (p < 10-24). GAS5 has been implicated in regulating transcriptional activity of the glucocorticoid receptor and has multiple functions related to apoptosis, immune function and various cancers. Endophenotypic analyses using peripheral cortisol levels and neuroimaging paradigms showed that methylomic variation in GAS5 network-related probes were associated with stress phenotypes. Postmortem brain analyses documented increased GAS5 expression in the amygdala of individuals with AUD. Our data suggest that alcohol use is associated with differential methylation in the glucocorticoid system that might influence stress and inflammatory reactivity and subsequently risk for AUD.

Epigenetic aging is accelerated in alcohol use disorder and regulated by genetic variation in APOL2.

To investigate the potential role of alcohol use disorder (AUD) in aging processes, we employed Levine's epigenetic clock (DNAm PhenoAge) to estimate DNA methylation age in 331 individuals with AUD and 201 healthy controls (HC). We evaluated the effects of heavy, chronic alcohol consumption on epigenetic age acceleration (EAA) using clinical biomarkers, including liver function test enzymes (LFTs) and clinical measures. To characterize potential underlying genetic variation contributing to EAA in AUD, we performed genome-wide association studies (GWAS) on EAA, including pathway analyses. We followed up on relevant top findings with in silico expression quantitative trait loci (eQTL) analyses for biological function using the BRAINEAC database. There was a 2.22-year age acceleration in AUD compared to controls after adjusting for gender and blood cell composition (p = 1.85 × 10-5). This association remained significant after adjusting for race, body mass index, and smoking status (1.38 years, p = 0.02). Secondary analyses showed more pronounced EAA in individuals with more severe AUD-associated phenotypes, including elevated gamma-glutamyl transferase (GGT) and alanine aminotransferase (ALT), and higher number of heavy drinking days (all ps < 0.05). The genome-wide meta-analysis of EAA in AUD revealed a significant single nucleotide polymorphism (SNP), rs916264 (p = 5.43 × 10-8), in apolipoprotein L2 (APOL2) at the genome-wide level. The minor allele A of rs916264 was associated with EAA and with increased mRNA expression in hippocampus (p = 0.0015). Our data demonstrate EAA in AUD and suggest that disease severity further accelerates epigenetic aging. EAA was associated with genetic variation in APOL2, suggesting potential novel biological mechanisms for age acceleration in AUD.

New Repeat Polymorphism in the AKT1 Gene Predicts Striatal Dopamine D2/D3 Receptor Availability and Stimulant-Induced Dopamine Release in the Healthy Human Brain.

The role of the protein kinase Akt1 in dopamine neurotransmission is well recognized and has been implicated in schizophrenia and psychosis. However, the extent to which variants in the AKT1 gene influence dopamine neurotransmission is not well understood. Here we investigated the effect of a newly characterized variant number tandem repeat (VNTR) polymorphism in AKT1 [major alleles: L- (eight repeats) and H- (nine repeats)] on striatal dopamine D2/D3 receptor (DRD2) availability and on dopamine release in healthy volunteers. We used PET and [11C]raclopride to assess baseline DRD2 availability in 91 participants. In 54 of these participants, we also measured intravenous methylphenidate-induced dopamine release to measure dopamine release. Dopamine release was quantified as the difference in specific binding of [11C]raclopride (nondisplaceable binding potential) between baseline values and values following methylphenidate injection. There was an effect of AKT1 genotype on DRD2 availability at baseline for the caudate (F(2,90) = 8.2, p = 0.001) and putamen (F(2,90) = 6.6, p = 0.002), but not the ventral striatum (p = 0.3). For the caudate and putamen, LL showed higher DRD2 availability than HH; HL were in between. There was also a significant effect of AKT1 genotype on dopamine increases in the ventral striatum (F(2,53) = 5.3, p = 0.009), with increases being stronger in HH > HL > LL. However, no dopamine increases were observed in the caudate (p = 0.1) or putamen (p = 0.8) following methylphenidate injection. Our results provide evidence that the AKT1 gene modulates both striatal DRD2 availability and dopamine release in the human brain, which could account for its association with schizophrenia and psychosis. The clinical relevance of the newly characterized AKT1 VNTR merits investigation.SIGNIFICANCE STATEMENT The AKT1 gene has been implicated in schizophrenia and psychosis. This association is likely to reflect modulation of dopamine signaling by Akt1 kinase since striatal dopamine hyperstimulation is associated with psychosis and schizophrenia. Here, using PET with [11C]raclopride, we identified in the AKT1 gene a new variable number tandem repeat (VNTR) marker associated with baseline striatal dopamine D2/D3 receptor availability and with methylphenidate-induced striatal dopamine increases in healthy volunteers. Our results confirm the involvement of the AKT1 gene in modulating striatal dopamine signaling in the human brain. Future studies are needed to assess the association of this new VNTR AKT1 variant in schizophrenia and drug-induced psychoses.

A Prospective Cohort Study of Influences on Externalizing Behaviors Across Childhood: Results From a Nurse Home Visiting Randomized Controlled Trial.

OBJECTIVE: This study investigated genetic and environmental influences on behavior in a cohort of 600 children followed prenatally to 18 years. METHOD: A randomized controlled trial of prenatal/infancy nurse home visits (NHV) was conducted in 600 predominantly African American mothers and their firstborn children from Memphis, TN. Mothers were assessed in pregnancy for mental health (MH), self-efficacy, and mastery. Mothers reported longitudinally on smoking and alcohol/drug use. The functional polymorphisms SLC6A4 5-HTTLPR, FKBP5 rs1360780 and DRD2/ANKK1 rs1800497 were genotyped together with 186 ancestry informative markers. Composite externalizing disorders (ED) continuous total scores from the mother-report Achenbach Child Behavior Checklist were included as dependent variables in regression analyses for time points 2, 6, 12, and 18 years. RESULTS: Behaviors at younger ages strongly predicted later behaviors (p < .0001). Children whose mothers had high self-efficacy and had received NHV were better behaved at age 2 years. Poorer maternal MH adversely influenced ED up to 12 years, but at age 18 years, maternal mastery exerted a strong, positive effect (p = .0001). Maternal smoking was associated with worse ED at 6 and 18 years. Main and interactive effects of genetic polymorphisms varied across childhood: FKBP5 rs1360780 up to age 6, 5-HTTLPR from 6 to 12, and DRD2/ANKK1 rs1800497 from 2 to 18 years. CONCLUSION: Our study suggests that maternal MH and resilience measured in pregnancy have long-lasting effects on child behavior. Maternal smoking across childhood and genetic factors also play a role. NHV had a positive effect on early behavior. Our findings have implications for prevention of pathological behaviors in adulthood. Clinical trial registration information-Age-17 Follow-Up of Home Visiting Intervention; http://clinicaltrials.gov/; NCT00708695.

Association of the OPRM1 Variant rs1799971 (A118G) with Non-Specific Liability to Substance Dependence in a Collaborative de novo Meta-Analysis of European-Ancestry Cohorts.

The mu1 opioid receptor gene, OPRM1, has long been a high-priority candidate for human genetic studies of addiction. Because of its potential functional significance, the non-synonymous variant rs1799971 (A118G, Asn40Asp) in OPRM1 has been extensively studied, yet its role in addiction has remained unclear, with conflicting association findings. To resolve the question of what effect, if any, rs1799971 has on substance dependence risk, we conducted collaborative meta-analyses of 25 datasets with over 28,000 European-ancestry subjects. We investigated non-specific risk for "general" substance dependence, comparing cases dependent on any substance to controls who were non-dependent on all assessed substances. We also examined five specific substance dependence diagnoses: DSM-IV alcohol, opioid, cannabis, and cocaine dependence, and nicotine dependence defined by the proxy of heavy/light smoking (cigarettes-per-day >20 vs. ≤ 10). The G allele showed a modest protective effect on general substance dependence (OR = 0.90, 95% C.I. [0.83-0.97], p value = 0.0095, N = 16,908). We observed similar effects for each individual substance, although these were not statistically significant, likely because of reduced sample sizes. We conclude that rs1799971 contributes to mechanisms of addiction liability that are shared across different addictive substances. This project highlights the benefits of examining addictive behaviors collectively and the power of collaborative data sharing and meta-analyses.

A genetically modulated, intrinsic cingulate circuit supports human nicotine addiction.

Whole-genome searches have identified nicotinic acetylcholine receptor alpha5-alpha3-beta4 subunit gene variants that are associated with smoking. How genes support this addictive and high-risk behavior through their expression in the brain remains poorly understood. Here we show that a key alpha5 gene variant Asp398Asn is associated with a dorsal anterior cingulate-ventral striatum/extended amygdala circuit, such that the "risk allele" decreases the intrinsic resting functional connectivity strength in this circuit. Importantly, this effect is observed independently in nonsmokers and smokers, although the circuit strength distinguishes smokers from nonsmokers, predicts addiction severity in smokers, and is not secondary to smoking per se, thus representing a trait-like circuitry biomarker. This same circuit is further impaired in people with mental illnesses, who have the highest rate of smoking. Identifying where and how brain circuits link genes to smoking provides practical neural circuitry targets for new treatment development.

The influence of GABRA2, childhood trauma, and their interaction on alcohol, heroin, and cocaine dependence.

BACKGROUND: The GABRA2 gene has been implicated in addiction. Early life stress has been shown to alter GABRA2 expression in adult rodents. We hypothesized that childhood trauma, GABRA2 variation, and their interaction would influence addiction vulnerability. METHODS: African-American men were recruited for this study: 577 patients with lifetime DSM-IV single and comorbid diagnoses of alcohol, cocaine, and heroin dependence, and 255 control subjects. The Childhood Trauma Questionnaire (CTQ) was administered. Ten GABRA2 haplotype-tagging single-nucleotide polymorphisms (SNPs) were genotyped. RESULTS: We found that exposure to childhood trauma predicted substance dependence (p < .0001). Polysubstance dependence was associated with the highest CTQ scores (p < .0001). The African Americans had four common haplotypes (frequency: .11-.30) within the distal haplotype block: two that correspond to the Caucasian and Asian yin-yang haplotypes, and two not found in other ethnic groups. One of the unique haplotypes predicted heroin addiction, whereas the other haplotype was more common in control subjects and seemed to confer resilience to addiction after exposure to severe childhood trauma. The yin-yang haplotypes had no effects. Moreover, the intron 2 SNP rs11503014, not located in any haplotype block and potentially implicated in exon splicing, was independently associated with addiction, specifically heroin addiction (p < .005). Childhood trauma interacted with rs11503014 variation to influence addiction vulnerability, particularly to cocaine (p < .005). CONCLUSIONS: Our results suggest that at least in African-American men, childhood trauma, GABRA2 variation, and their interaction play a role in risk-resilience for substance dependence.

Disrupted in schizophrenia 1 genotype and positive symptoms in schizophrenia.

BACKGROUND: Converging evidence has demonstrated an association between the Disrupted in Schizophrenia 1 (DISC1) gene and schizophrenia (SZ). Within the DISC1 gene, a single nucleotide polymorphism (SNP), Ser704Cys, has been associated with the structure and function of the hippocampus. Because positive symptoms in SZ have also been associated with hippocampal structure and function, we hypothesized that variation in a DISC1 haplotype containing Ser704Cys would be significantly associated with positive symptomatology in SZ. METHODS: We tested for an association between variation in a haplotype block within the DISC1 gene containing Ser704Cys and lifetime history of positive symptoms in 199 Caucasian patients with SZ. RESULTS: We detected significant associations between a DISC1 haplotype containing Ser704Cys and Ser704Cys genotype and lifetime severity of delusions in SZ. CONCLUSIONS: These data suggest that that the effect of DISC1 genetic variation might be associated with positive symptoms in patients with SZ.

The FEZ1 gene shows no association to schizophrenia in Caucasian or African American populations.

Schizophrenia is a complex psychiatric disorder with both genetic and environmental components and is thought to be in part neurodevelopmental in origin. The DISC1 gene has been linked to schizophrenia in two independent Caucasian populations. The DISC1 protein interacts with a variety of proteins including FEZ1, the mammalian homolog of the Caenorhabditis elegans unc-76 protein, which is involved in axonal outgrowth. Variation at the FEZ1 gene has been associated with schizophrenia in a large Japanese cohort. In this study, nine SNP markers at the FEZ1 locus were genotyped in two populations. A North American Caucasian cohort of 212 healthy controls, 178 schizophrenics, 79 bipolar disorder, and 58 with schizoaffective disorder, and an African American cohort of 133 healthy controls, 162 schizophrenics, and 28 with schizoaffective disorder. No association to schizophrenia, bipolar disorder or schizoaffective disorder was found for any of the nine markers typed in these populations at the allelic or the genotypic level. Additionally no association was found in either population between specific haplotypes and any of the psychiatric disorders. Variation at the FEZ1 locus does not play a significant role in the etiology of schizophrenia, bipolar disorder or schizoaffective disorder in North American Caucasian or African American populations.Neuropsychopharmacology (2007) 32, 190-196. doi:10.1038/sj.npp.1301177; published online 16 August 2006.