Val/Met BDNF as a genetic risk for a false sense of security in post-discharge suicide risk.

BACKGROUND: The time after discharge from psychiatric inpatient care is one of the most dangerous periods in terms of suicide risk. Predicting who is at higher risk could help with resource allocation to assure patients at high risk of suicide attempts are most closely followed. We previously showed that inpatients who improve their suicide ideation levels faster while in inpatient treatment are the ones with highest rates of post-discharge suicide. Here, we studied the possible genetic underpinnings associated with such risk. METHOD: We recorded the slope of suicide ideation recovery of 710 psychiatric inpatients from which we studied two genetic variants likely associated with suicide risk: The serotonin transporter variant 5-HTTLPR, and the BDNF gene variant Val66Met. RESULTS: We found that inpatients carrying the BDNF Met variant (hypothesized as conferring higher suicide risk) improved their suicide ideation scores faster than Val/Val carrying inpatients. No significant association was found for 5-HTTLPR. LIMITATIONS: The present sample was genetically homogenous, and future research should replicate these findings on a more diverse sample. CONCLUSIONS: In conclusion, we found a paradoxical result: Carrying the BDNF Met variant allows inpatients to improve faster, which was shown to confer higher risk at the post-discharge period. This may explain some inconsistencies in the literature in terms of the role of BDNF in suicide ideation and attempts.

Emotional self-regulation, impulsivity, 5-HTTLPR and tobacco use behavior among psychiatric inpatients.

BACKGROUND: While the serotonin transporter (SLC6A4) gene, 5-HTTLPR, interacts with the social environment to influence both emotional self-regulation and smoking behavior, less is known about interactions between emotional self-regulation and 5-HTTLPR or their joint influence on tobacco use. Here, we examined such interactions among psychiatric inpatients, the population with the highest rates of smoking. METHODS: Participants (506 adults) were psychiatric inpatients at The Menninger Clinic in Houston TX between 2012 and 16. Most were white (89%), male (55%), with a mean age of 32.3 years. Participants completed the Difficulties in Emotional Regulation Scale (DERS) at admission. We examined interactions with smoking among three DERS subscales and 5-HTTLPR, controlling for sex, race and age. RESULTS: Smoking rates were higher among those with the 5-HTTPLR L'L' genotype compared to peers carrying an S' allele (47.9% vs. 37.4%, respectively). Among S' allele carrying participants, impulse control difficulties (OR = 1.09; 95%CI: 1.03-1.14) and lack of emotion clarity (OR = 1.06; 95%CI: 1.00-1.11) increased risk for ever using tobacco, while accessing more ways to regulate emotion (OR = 0.95; 95%CI: 0.92-0.99) offered a protective effect against ever using tobacco. Neither demographic nor DERS covariates were associated with using tobacco among the L'L' group. LIMITATIONS: This ethnically homogenous sample limits generalizability and using a binary outcome can over-estimate a gene environment interaction effect. CONCLUSIONS: Emotional self-regulation exerts a stronger influence on using tobacco among carriers of an S' allele of 5-HTTLPR than peers with the L'L' genotype. Promoting emotional self-regulatory skills may have benefits for preventing tobacco use.

Broad scale proteomic analysis of heat-destabilised symbiosis in the hard coral Acropora millepora.

Coral reefs across the globe are threatened by warming oceans. The last few years have seen the worst mass coral bleaching events recorded, with more than one quarter of all reefs irreversibly impacted. Considering the widespread devastation, we need to increase our efforts to understanding the physiological and metabolic shifts underlying the breakdown of this important symbiotic ecosystem. Here, we investigated the proteome (PRIDE accession # PXD011668) of both host and symbionts of the reef-building coral Acropora millepora exposed to ambient (~ 28 °C) and elevated temperature (~ 32 °C for 2 days, following a five-day incremental increase) and explored associated biomolecular changes in the symbiont, with the aim of gaining new insights into the mechanisms underpinning the collapse of the coral symbiosis. We identified 1,230 unique proteins (774 host and 456 symbiont) in the control and thermally stressed corals, of which 107 significantly increased and 125 decreased in abundance under elevated temperature relative to the control. Proteins involved in oxidative stress and proteolysis constituted 29% of the host proteins that increased in abundance, with evidence of impairment to endoplasmic reticulum and cytoskeletal regulation proteins. In the symbiont, we detected a decrease in proteins responsible for photosynthesis and energy production (33% of proteins decreased in abundance), yet minimal signs of oxidative stress or proteolysis. Lipid stores increased > twofold despite reduction in photosynthesis, suggesting reduced translocation of carbon to the host. There were significant changes in proteins related to symbiotic state, including proteins linked to nitrogen metabolism in the host and the V-ATPase (-0.6 fold change) known to control symbiosome acidity. These results highlight key differences in host and symbiont proteomic adjustments under elevated temperature and identify two key proteins directly involved in bilateral nutrient exchange as potential indicators of symbiosis breakdown.

Bidirectional translational research: Progress in understanding addictive diseases.

The focus of this review is primarily on recent developments in bidirectional translational research on the addictions, within the Laboratory of the Biology of Addictive Diseases at The Rockefeller University. This review is subdivided into major interacting aspects, including (a) Investigation of neurobiological and molecular adaptations (e.g., in genes for the opioid receptors or endogenous neuropeptides) in response to cocaine or opiates, administered under laboratory conditions modeling chronic patterns of human self-exposure (e.g., chronic escalating "binge"). (b) The impact of such drug exposure on the hypothalamic-pituitary-adrenal (HPA) axis and interacting neuropeptidergic systems (e.g., opioid, orexin and vasopressin). (c) Molecular genetic association studies using candidate gene and whole genome approaches, to define particular systems involved in vulnerability to develop specific addictions, and response to pharmacotherapy. (d) Neuroendocrine challenge studies in normal volunteers and current addictive disease patients along with former addicts in treatment, to investigate differential pharmacodynamics and responsiveness of molecular targets, in particular those also investigated in the experimental and molecular genetic approaches as described above.

Genotype patterns that contribute to increased risk for or protection from developing heroin addiction.

A genome-wide association study was conducted using microarray technology to identify genes that may be associated with the vulnerability to develop heroin addiction, using DNA from 104 individual former severe heroin addicts (meeting Federal criteria for methadone maintenance) and 101 individual control subjects, all Caucasian. Using separate analyses for autosomal and X chromosomal variants, we found that the strongest associations of allele frequency with heroin addiction were with the autosomal variants rs965972, located in the Unigene cluster Hs.147755 (experiment-wise q=0.053), and rs1986513 (q=0.187). The three variants exhibiting the strongest association with heroin addiction by genotype frequency were rs1714984, located in an intron of the gene for the transcription factor myocardin (P=0.000022), rs965972 (P=0.000080) and rs1867898 (P=0.000284). One genotype pattern (AG-TT-GG) was found to be significantly associated with developing heroin addiction (odds ratio (OR)=6.25) and explained 27% of the population attributable risk for heroin addiction in this cohort. Another genotype pattern (GG-CT-GG) of these variants was found to be significantly associated with protection from developing heroin addiction (OR=0.13), and lacking this genotype pattern explained 83% of the population attributable risk for developing heroin addiction. Evidence was found for involvement of five genes in heroin addiction, the genes coding for the mu opioid receptor, the metabotropic receptors mGluR6 and mGluR8, nuclear receptor NR4A2 and cryptochrome 1 (photolyase-like). This approach has identified several new genes potentially associated with heroin addiction and has confirmed the role of OPRM1 in this disease.

Vulnerability of seagrass blue carbon to microbial attack following exposure to warming and oxygen.

Seagrass meadows store globally-significant quantities of organic 'blue' carbon. These blue carbon stocks are potentially vulnerable to anthropogenic stressors (e.g. coastal development, climate change). Here, we tested the impact of oxygen exposure and warming (major consequences of human disturbance) on rates of microbial carbon break-down in seagrass sediments. Active microbes occurred throughout seagrass sediment profiles, but deep, ancient sediments (~5000 yrs. old) contained only 3% of the abundance of active microbes as young, surface sediments (<2 yrs. old). Metagenomic analysis revealed that microbial community structure and function changed with depth, with a shift from proteobacteria and high levels of genes involved in sulfur cycling in the near surface samples, to a higher proportion of firmicutes and euraracheota and genes involved in methanogenesis at depth. Ancient carbon consisted almost entirely (97%) of carbon considered 'thermally recalcitrant', and therefore presumably inaccessible to microbial attack. Experimental warming had little impact on carbon; however, exposure of ancient sediments to oxygen increased microbial abundance, carbon uptake and sediment carbon turnover (34-38 fold). Overall, this study provides detailed characterization of seagrass blue carbon (chemical stability, age, associated microbes) and suggests that environmental disturbances that expose coastal sediments to oxygen (e.g. dredging) have the capacity to diminish seagrass sediment carbon stocks by facilitating microbial remineralisation.

Epigenetic variation in OPRM1 gene in opioid-exposed mother-infant dyads.

Neonatal abstinence syndrome (NAS) due to in-utero opioid exposure has significant variability of severity. Preliminary studies have suggested that epigenetic variation within the µ-opioid receptor (OPRM1) gene impacts NAS. We aimed to determine if DNA methylation in OPRM1 within opioid-exposed mother-infant dyads is associated with differences in NAS severity in an independent cohort. Full-term opioid-exposed newborns and their mothers (N = 68 pairs) were studied. A DNA sample was obtained and then assessed for level of DNA methylation at 20 CpG sites within the OPRM1 promoter region by next-generation sequencing. Infants were monitored for NAS and treated with replacement opioids according to institutional protocol. The association between DNA methylation level at each CpG site with NAS outcome measures was evaluated using linear and logistic regression models. Higher methylation levels within the infants at the -18 (11.4% vs 4.4%, P = .0001), -14 (46.1% vs 24.0%, P = .002) and +23 (26.3% vs 12.9%, P = .008) CpG sites were associated with higher rates of infant pharmacologic treatment. Higher levels of methylation within the mothers at the -169 (R = 0.43, P = .008), -152 (R = 0.40, P = .002) and +84 (R = 0.44, P = .006) sites were associated point-wise with longer infant length of stay. Maternal associations remained significant point-wise for -169 (ß = 0.07, P = .007) and on an experiment-wise level for +84 (ß = -0.10, P = .003) using regression models. These results suggest an association of higher levels of OPRM1 methylation at specific CpG sites and increased NAS severity, replicating prior findings. These findings have important implications for personalized treatment regimens for infants at high risk for severe NAS.

Estradiol and estrogen receptor-dependent stabilization of a minivitellogenin mRNA lacking 5,100 nucleotides of coding sequence.

We have developed a transfection assay to investigate the estrogen-mediated stabilization of cytoplasmic vitellogenin mRNA. A minivitellogenin (MV5) gene containing the 5' and 3' untranslated and coding regions but lacking 5,075 nucleotides of internal coding sequence was constructed. Cotransfection of the MV5 plasmid and a Xenopus estrogen receptor expression plasmid into Xenopus liver tissue culture cells yielded a 529-nucleotide MV5 mRNA, which was specifically stabilized by estrogen. MV5 mRNA exhibited the increased stability indicative of positive regulation when the estradiol-estrogen receptor complex was present and was not destabilized by unliganded estrogen receptor. Transfected estrogen receptor, estradiol, and 529 nucleotides of the 5,604-nucleotide vitellogenin B1 mRNA were sufficient for stabilization.

INTEGRATIVE BAYESIAN ANALYSIS OF NEUROIMAGING-GENETIC DATA THROUGH HIERARCHICAL DIMENSION REDUCTION.

Advances in neuromedicine have emerged from endeavors to elucidate the distinct genetic factors that influence the changes in brain structure that underlie various neurological conditions. We present a framework for examining the extent to which genetic factors impact imaging phenotypes described by voxel-wise measurements organized into collections of functionally relevant regions of interest (ROIs) that span the entire brain. Statistically, the integration of neuroimaging and genetic data is challenging. Because genetic variants are expected to impact different regions of the brain, an appropriate method of inference must simultaneously account for spatial dependence and model uncertainty. Our proposed framework combines feature extraction using generalized principal component analysis to account for inherent short- and long-range structural dependencies with Bayesian model averaging to effectuate variable selection in the presence of multiple genetic variants. The methods are demonstrated on a cocaine dependence study to identify ROIs associated with genetic factors that impact diffusion parameters.

Isolation and characterization of murine vav2, a member of the vav family of proto-oncogenes.

We describe the isolation and characterization of a cDNA encoding murine vav2. vav2 shares 63% and 55% identity at the nucleic acid and amino acid levels, respectively, with vav, a proto-oncogene that plays an essential role in embryonic development and hematopoietic signal transduction. The 100 kDa Vav2 protein contains the characteristic array of structural motifs found in Vav. However, unlike vav, vav2 transcripts are widely distributed in both hematopoietic and non-hematopoietic tissues. In the adult, vav2 mRNA is found at high levels in the spleen, liver, testes and placenta. Northern blot analysis reveals two vav2 mRNA species (designated alpha and beta). The alpha species is expressed throughout development while the alpha and beta species are expressed tissue-specifically in adults. Transfection of NIH3T3 cells with expression vectors containing vav2 deletions demonstrate that elimination of 183 amino terminal residues of Vav2 is sufficient to activate its oncogenic potential. Vav2-induced transformation is characterized by the appearance of foci composed of cells in which cytokinesis and karyokinesis are uncoupled. This phenotype is comparable, but not identical, to morphological changes induced by Vav and other members of the DbI family of oncoproteins. Our results suggest that Vav family members mediate functions important in the regulation of cell architecture and proliferation in most, if not all, tissues.

Sorting of pancreatic islet cell subpopulations by light scattering using a fluorescence-activated cell sorter.

Methods have been developed for the preparation of suspensions of viable rat pancreatic islet cells and their analysis and sorting in the fluorescence-activated cell sorter (FACS III or IV). Histograms of cell number versus light scattering in a near forward angle (1-15 degrees) demonstrated that viable islet cells produce a broad peak that is distinctly separated from the peaks generated by exocrine cells, erythrocytes, and nonviable cells. Electron microscopic examination and radioimmunoassay of hormone content in fractions collected across the peak showed that glucagon-containing (A) cells scatter less intensely and are concentrated within the left side of the islet cell peak, while somatostatin-containing (D) cells are localized to the far right side, indicating a higher intrinsic light scattering property of the D-cells. The more abundant insulin-containing (B) cells define the center of the islet cell peak. Sodium dodecyl sulfate slab gel electrophoresis and radioautography of 35S-methionine labeled cellular proteins confirmed that sorted cells are viable. Cells from the far left region contained increased amounts of labeled 18 Kd proglucagon and its 13-Kd and 10-Kd conversion intermediates, while cells from the right side were relatively enriched in labeled 12.4 Kd prosomatostatin. These results demonstrate that intrinsic light scattering alone can be used to prepare A- or D-cell enriched fractions from islets for biochemical analysis.

Suicidality and 5-hydroxyindoleacetic acid concentration associated with a tryptophan hydroxylase polymorphism.

BACKGROUND: To examine whether the tryptophan hydroxylase (TPH) gene, which codes for the rate-limiting enzyme in the biosynthesis of serotonin, may be a factor influencing serotonin turnover and behaviors controlled by serotonin. METHODS: Using a polymerase chain reaction-based method, TPH genotype was determined in DNA samples from 56 impulsive and 14 nonimpulsive, alcoholic, violent offenders and 20 healthy volunteers. RESULTS: In the behaviorally extreme impulsive group, we observed a significant association between TPH genotype and cerebrospinal fluid 5-hydroxyindoleacetic acid (5-HIAA) concentration. No association of TPH genotype with impulsive behavior was detected. The polymorphism was also associated with a history of suicide attempts in all violent offenders, independent of impulsivity status and cerebrospinal fluid 5-HIAA concentration. CONCLUSION: In some individuals, a genetic variant of the TPH gene may influence 5-HIAA concentration in the cerebrospinal fluid and predisposition to suicidal behavior.

A tryptophan hydroxylase gene marker for suicidality and alcoholism.

BACKGROUND: Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the synthesis of serotonin. Low turnover rate of this monoamine neurotransmitter is associated with impaired impulse control. We previously reported that, in Finns, TPH genotype was associated with suicidality, a pathophysiological mechanism that may involve impaired impulse control. METHODS: Association and sib-pair linkage analyses of a polymorphism in intron 7 of the TPH gene with suicidality, alcoholism, and the Karolinska Scales of Personality were conducted in 804 Finnish alcoholic offenders, controls, and their relatives, in a sample that included 369 sib pairs. RESULTS: The association of the TPH 17 779C (L) allele to suicidality in impulsive offenders reported previously was replicated in a new group of Finnish offenders (P=.001, n=122). The intron 7 variant in the TPH gene showed significant evidence for linkage to suicidality (P=.006 in unaffected sib pairs), severe suicide attempts (P=.006 in unaffected sib pairs; regression: P=.01), alcoholism (P=.003 in unaffected sib-pairs; regression: P=.02), and Karolinska Scales of Personality socialization score (regression: P=.002). CONCLUSIONS: The status of the TPH A779C allele as a marker for suicidality was replicated and linkage with alcoholism and Karolinska Scales of Personality socialization score was also observed. A functional variant(s) in or close to the TPH gene may predispose individuals to suicidality and other behaviors thought to be influenced by serotonin.

No coding variant of the tryptophan hydroxylase gene detected in seasonal affective disorder, obsessive-compulsive disorder, anorexia nervosa, and alcoholism.

BACKGROUND: The goal of this study was to evaluate the role of genetic variation in the coding sequence of tryptophan hydroxylase (TPH) in the pathogenesis of several psychiatric diseases in which altered serotonin function has been implicated: bipolar affective disorder (BP), obsessive-compulsive disorder (OCD), anorexia nervosa (AN), seasonal affective disorder (SAD), panic disorder (PD), and alcoholism (Alc). METHODS: Ninety-three percent of the TPH coding sequence was screened by polymerase chain reaction single-strand conformation polymorphism (SSCP) for DNA sequence variations in 128 AN, 88 OCD, 72 SAD, 45 PD, and 36 BP patients and 142 normal volunteers. Also included in the screening were 61 Alc randomly selected from a Finnish alcoholic population in which an association of a TPH intron 7 polymorphism with suicidality was previously observed. Polymorphisms detected by SSCP were characterized by DNA sequencing and by allele-specific restriction enzyme digestion. Genotyping was then performed in 34 Finnish alcoholic suicide attempters. RESULTS: A rare silent mutation was identified in exon 10 and is designated T1095C. The C1095 allele was found in 1 OCD and in 2 AN subjects; all 3 individuals were heterozygous (C1095/T1095) for the variant allele. No association was observed between this TPH T1095C variant with either OCD, AN, Alc, or suicidality. CONCLUSION: These results suggest that the coding sequence of the TPH gene does not contain abundant variants, and may not play a major role in vulnerability to several psychopathologies in which reduced serotonin turnover has been implicated.

Possible association of a polymorphism of the tryptophan hydroxylase gene with suicidal behavior in depressed patients.

OBJECTIVE: This study was designed to test the hypothesis that serotonin-system-related genes may be correlated with suicide risk. METHOD: Fifty-one unrelated Caucasian inpatients with major depression, with or without a history of suicidal acts, were genotyped for a biallelic polymorphism at the tryptophan hydroxylase locus. RESULTS: The less common tryptophan hydroxylase U allele occurred with greater frequency in the patients who had attempted suicide. A logistic regression analysis confirmed an association between tryptophan hydroxylase genotype and lifetime history of suicide attempts. CONCLUSIONS: Serotonergic-system-related genes may influence the risk of suicide in persons with major depression.

Agonist-promoted down-regulation and functional desensitization in two naturally occurring variants of the human serotonin1A receptor.

We recently reported two naturally occurring polymorphisms of the human serotonin1A (5-HT1A) receptor: glycine22-->serine (Ser22) and isoleucine28-->valine (Val28) in the putative aminoterminal domain of the receptor. To investigate the regulatory properties of these variants, the wild type (WT) and variant 5-HT1A receptors were stably expressed in CHO-K1 cells. WT, Ser22, and Val28 displayed similar high-affinity binding to [3H]-8-OH-DPAT. Competition experiments with 5-HT1A agonists and antagonists demonstrated similar pharmacological profiles. Receptor agonist-promoted down-regulation was tested by exposure to 100 mumol/L 8-OH-DPAT. After 24-h exposure, WT and Val28 underwent 59.3 +/- 3.9% and 59.5 +/- 1.4% reduction in receptor density respectively, whereas the degree of down-regulation was significantly lower for Ser22 (21.4 +/- 4.2%). Cell treatment for 24 h with 100 mumol/L 8-OH-DPAT reduced the 5-HT-induced inhibition of cAMP accumulation by 24.9 +/- 5.1% for WT and 16.4 +/- 0.8% for Val28, but only by 4.8 +/- 3% for Ser22. We conclude that the Ser22 variant is capable of attenuating agonist-mediated receptor down-regulation and desensitization.

Tryptophan hydroxylase genotype is associated with impulsive-aggression measures: a preliminary study.

To assess the relationship between two phenotypes in an extremely well-characterized population of personality disorder patients-impulsive aggression and prolactin response to fenfluramine-and tryptophan hydroxylase (TPH) genotype, TPH genotype (at an intronic polymorphic site) and prolactin response to fenfluramine were assessed in 40 Caucasian patients with personality disorder. Impulsive aggression was assessed by using the Buss-Durkee Hostility Inventory (BDHI). Twenty-one male patients with the "LL" genotype had higher BDHI scores than men with the "UL" or the "UU" genotype. No relationship between genotype and prolactin response to fenfluramine was found. It was concluded that impulsive-aggressive behavior in male personality disorder patients may be associated with the TPH genotype.

Sequence, splice site and population frequency distribution analyses of the polymorphic human tryptophan hydroxylase intron 7.

A human tryptophan hydroxylase intron seven polymorphism previously associated with low CSF 5-HIAA and suicidal behavior was sequenced and characterized for its potential role in TPH pre-mRNA splicing. Two polymorphic sites were identified: A218C and A779C. The 779A allelic frequency in various populations ranged from 0.43 to 0.61 and was in strong linkage disequilibrium with the A218C site. A218C provides a site for restriction fragment length polymorphism analysis. TPH mRNA was reverse-transcribed and sequenced. No aberrant splice products from the 779A or 779G TPH genes were detected nor were any other polymorphic nucleotides found.

Antisense oligonucleotide inhibition of tryptophan hydroxylase activity in mouse brain.

To examine in vivo effectiveness of antisense oligonucleotides against tryptophan hydroxylase (TPH) mRNA, adult male swiss-NIH mice were implanted with in-dwelling cannula into the 4th ventricle and after recovery infused with either antisense oligonucleotide to TPH, scrambled control oligo or saline vehicle for four consecutive days. An additional group of animals bearing cannula were injected a single time i.p. with the TPH inhibitor para-chlorophenylalanine (PCPA; 300 mg/kg). All animals were sacrificed on the afternoon of the 4th day of treatment. TPH activity was measured by enzymatic assay and HPLC quantification of end-product synthesis. There was a significant decrease (> 50%) in TPH activity in both the PCPA-treated and antisense-oligo infused animals compared to either scrambled-oligo or saline-infused subjects (ANOVA; P < 0.05). There was no difference between saline and scrambled oligo-infusion. In a separate group of animals treated in the same way, behavioral tests were conducted on the afternoon of the 4th day. Two tests of anxiety, the hole-board apparatus and the elevated plus-maze, indicated some significant effects of PCPA treatment and/or antisense oligo-infusion but confounding effects due to alterations in locomotion could not be ruled out. However, tests on a rotorod apparatus indicated that antisense oligo-infused animals retained good balance and coordination in that their performance significantly improved on the second test, as did that of scrambled-oligo infused animals. In contrast, PCPA-treated animals did not improve, suggesting that locomotor performance had been impaired. These data support the notion that antisense oligo blockade may offer advantages over pharmacological manipulations of enzyme activity.

A variant in ANKK1 modulates acute subjective effects of cocaine: a preliminary study.

This study aimed to evaluate whether functional variants in the ankyrin repeat and kinase domain-containing 1 (ANKK1) gene and/or the dopamine receptor D2 (DRD2) gene modulate the subjective effects (reward or non-reward response to a stimulus) produced by cocaine administration. Cocaine-dependent participants (N = 47) were administered 40 mg of cocaine or placebo at time 0, and a subjective effects questionnaire (visual analog scale) was administered 15 min prior to cocaine administration, and at 5, 10, 15 and 20 min following administration. The influence of polymorphisms in the ANKK1 and DRD2 genes on subjective experience of cocaine in the laboratory was tested. Participants with a T allele of ANKK1 rs1800497 experienced greater subjective 'high' (P = 0.00006), 'any drug effect' (P = 0.0003) and 'like' (P = 0.0004) relative to the CC genotype group. Although the variant in the DRD2 gene was shown to be associated with subjective effects, linkage disequilibrium analysis revealed that this association was driven by the ANKK1 rs1800497 variant. A participant's ANKK1 genotype may identify individuals who are likely to experience greater positive subjective effects following cocaine exposure, including greater 'high' and 'like', and these individuals may have increased vulnerability to continue using cocaine or they may be at greater risk to relapse during periods of abstinence. However, these results are preliminary and replication is necessary to confirm these findings.