Of particular interest to this study is a common polymorphism involving a Val to Met substitution at codon 158. The Val allele of the COMT Val158Met polymorphism is 40% more enzymatically active than the Met allele. Thus, carriers of the Met allele metabolize dopamine at a less efficient rate, resulting in higher levels of dopamine in the synapse and ultimately an escalation in dopamine receptor activation. This differentiation of dopamine receptor activity dependent on COMT genotype has led to several investigations into the relationship between COMT and executive dysfunction in which the Val allele has been putatively linked to poor performance on executive functioning tasks. However, to our knowledge no work has examined the relationship between COMT and sexual risk behavior; albeit studies of similar behaviors such as novelty seeking, reward dependence, as well as affective arousal and regulation have demonstrated significant relationships. Given the aforementioned paucity of research in the current literature addressing the contribution of genetic and neurocognitive factors on sexual risk behavior, the primary aim of this study was to examine the main effects of executive functioning as well as the main effects of the COMT Val158Met polymorphism on sexual risk behavior among a ethnically diverse population of men with and without METH dependence and/or HIV infection. Within this aim, we hypothesized that the highly active COMT Val/Val genotype and its putatively associated deficits in executive functioning would be independently associated with sexual risk behaviors. In addition, as a result of previously mentioned research that has demonstrated an association between COMT genotype and executive functioning we also explored the potential interaction effects of COMT and executive dysfunction on sexual risk behavior.Participants were volunteers evaluated at the HIV Neurobehavioral Research Center at the University of California in San Diego as part of a cohort study focused on central nervous system effects of HIV and methamphetamine. The current study comprised 192 sexually active non-monogamous men with and without methamphetamine dependence and/or HIV infection . Men were classified as nonmonogamous if they stated they had “no current partner” at time of assessment. Monogamous men were excluded because unsafe sexual behavior within a monogamous relationship is less risky than in non-monogamous relationships.
All participants underwent a comprehensive characterization procedure that included collection of demographic, neuromedical,hydroponic rack system psychiatric as well as neuropsychiatric information. HIV serological status was determined by enzyme linked immunosorbent assays plus a confirmatory test. Lifetime METH dependence was determined by the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders Version IV . However, participants were not actively using other substances, with the exception of cannabis and alcohol. Potential participants were excluded if they met lifetime dependence criteria for other drugs, unless the dependence was judged to be remote and episodic in nature by a doctoral level clinician. Alcohol dependence within the last year was also an exclusion criterion. All participants were seronegative for hepatitis C infection. Additional information for each participant was collected as it relates to current depressed mood as well as lifetime diagnosis of Major Depression Disorder and/or Bipolar Disorder I or II. Current depressed mood was assessed utilizing the Beck Depression Inventory-I and MDD and Bipolar Disorder were ascertained using the SCID-IV. Information was also collected to determine lifetime dependence on sedatives, cannabis, opioids, cocaine,hallucinogens, and alcohol, using the SCID-IV. For METH+ participants, additional information was collected regarding age at first use, years of use, and days since last use of METH; whereas for HIV+ participants, HIV RNA plasma copies was ascertained as part of a larger neuromedical evaluation. All participants gave written consent prior to enrollment and all procedures were approved by the Human Research Protection Program of the University of California, San Diego and San Diego State University.Executive functioning was determined as part of a larger comprehensive battery of tests covering seven ability domains . The executive functioning domain deficit score, of particular focus in this study, was made up of perseverative responses on the Wisconsin Card Sorting Test; errors on the Halstead Category Test, which measures abstraction and cognitive flexibility; and time to complete the Trail Making Test part B, reflecting ability to switch and maintain attention between ongoing sequences.
Raw scores for each of these component tests were converted to demographically-adjusted T-scores , including adjustments for age, education, gender, and ethnicity as available for each test. The demographically adjusted T-scores for each test were then converted into deficit scores, which reflect degree of impairment by setting performances within the normal range at zero with a range from 0 to 5 . Finally, the individual deficit scores were averaged to derive the domain deficit score, which reflects the severity of executive functioning deficit. Previous work has demonstrated that deficit scores achieve good diagnostic agreement with classifications made by blind clinical ratings. All neurocognitive testing and scoring was performed by trained psychometrists blinded to participants’ genotypes.A multiplex PCR technique designed using Sequenom SpectroDESIGNER software was employed by inputting a sequence containing 100 bp of flanking sequence on either side of the COMT Val158Met polymorphism. The SNP was then grouped into multiplexes so that the extended product would not overlap in mass with any other oligonucleotide present in the reaction mix, and where no primer-primer, primer-product, or nonspecific interactions would occur. The PCR was carried out in 384-well reaction plates in a volume of 5 μl using 10 ng genomic or whole-genome amplified DNA. All subsequent steps, up until the reaction, were spotted onto the SpectroCHIP and carried out in the same reaction plate. After PCR, any unincorporated dNTPs from the PCR were removed from the reaction by digestion with Shrimp alkaline phosphatase. dNTPs were removed so that they could not play any role in the extension of the oligonucleotide at the SNP site. The extension reaction was then carried out in the presence of the extension oligonucleotide and a termination mix containing mass-modified dideoxynucleotides which extended the oligonucleotide over the SNP site with one base. Before spotting onto the SpectroCHIP, the reaction was cleaned by incubation with a cation-exchange resin which removed any salts present. The extension product was then spotted onto a 384-well spectroCHIP before being flown in the MALDI-TOF mass spectrometer. Data were collected, in real time, using SpectroTYPER Analyzer 3.3.0.15, SpectraAQUIRE 3.3.1.1 and SpectroCALLER 3.3.0.14 algorithms.
All statistical tests and procedures were conducted using SPSS 10.0 . Univariate comparisons across the three COMT genotypes were performed using one-way analysis of variance for continuous and chi-squared tests for categorical variables. In cases, where data violated normality assumptions medians were calculated and nonparametric tests performed. To examine the main and explore the interaction effects of executive functioning and COMT on sexual risk behaviors, hierarchical multiple linear regressions in accord with Barron and Kenny’s approach were conducted for each of the seven sexual risk behaviors under study. Prior to running each analysis, the executive functioning variable was centered and the COMT genotype contrast coded to reduce problems resulting from multi-collinearity . In addition, interaction terms were created by multiplying COMT genotype by the centered executive functioning variable. Next, multiple linear regressions were used to examine potential confounders based on univariate genotype comparisons described above. These confounders included: ethnicity, METH status, HIV status and age at first intercourse. We also included BDI scores based on inclusion of this measure in recent work testing a similar hypothesis. Results showed that METH status, HIV status,rolling benches canada and age at first intercourse accounted for a significant unique variance for all sexual behaviors under investigation . Thus to control for these potential confounding effects, the residuals derived from each of the sexual behavior models were used as the dependent variables for all subsequent regression models. The centered executive functioning variable and COMT genotype as well as the new interaction term were then entered as independent variables into seven individual hierarchical multiple regression models using the residuals described above as the dependent variable. For models in which a significant interaction was observed, a final round of regressions were conducted stratified by COMT genotype to determine the nature of the interaction between executive functioning and COMT on the particular sexual risk behavior. Due to the exploratory nature of the interaction analysis we selected a relaxed alpha threshold alpha < .10 to reduce Type II errors, albeit the traditional alpha threshold of .05 was used for all other analyses.To our knowledge this study is the first to examine main effects as well as explore the interaction effects of COMT genotype and executive functioning on sexual risk behavior. Our main findings suggest significant executive dysfunction main effects for number of sexual partners as well as frequency of oral sex and condom use. In addition, results of our exploratory interaction analyses provide evidence that COMT genotype and executive dysfunction interact in models of number of sexual partners, condom use, insertive and receptive anal sex, as well as oral sex. Stratified analyses further suggest that the strength of these associations is dependent on the number of Met alleles the individual was carrying, with the exception of oral sex in which Val/Val was the informative genotype. Our significant executive dysfunction main effects for sexual risk behaviors are discordant with the only other study, to our knowledge, that has examined the association between executive dysfunction and sexual risk behavior. In that study, no association was found between executivedys function and sexual risk behavior among an African American sample of men and women poly-substance abusers with and without HIV infection. However, three major methodological differences may explain our discordant findings. First, Gonzalez et al.estimated sexual risk behavior in the past 6 months compared to our window of 12 months and also utilized a composite score rather than individual sexual risk behaviors as their dependent variable. Second, executive dysfunction was assessed using the Iowa Gambling Task, delayed non-matching to sample paradigm, and Stroop task-reaction time version which, respectively, measure decision-making, working memory, and response inhibition. Although these tests are well justified, other components of executive functioning such as perseveration, cognitive sequencing, and concept formation which were assessed in the current study, were not examined.
Third and finally, regression models were adjusted for sensation seeking, a factor shown in previous research to be associated with sexual risk behavior [34–37]; however, in the current study sensation seeking data was not available and was not adjusted for. Thus, future work examining the association between executive dysfunction and sexual risk behaviors are warranted; particularly research utilizing larger samples with diverse measures of executive functioning and models adjusting for sensation seeking and other personality covariates. Novel to the current study, we demonstrated several genotype by endophenotype interactions for sexual risk behaviors. A relaxed significance criterion produced significant interactions for number of sexual partners, condom use, insertive and receptive anal sex, as well as oral sex. These interactions collectively advocate for further investigation of genotypeendophenotype interactions for sexual risk behavior. However, due to the exploratory nature of these interactions our discussion will be confined to interactions observed for number of sexual partners, frequency of insertive anal sex and condom use, as interactions observed in these models met the traditional significance criterion . We observed both a main and interaction effect for number of sexual partners, albeit only within the model including the composite executive functioning deficit score. In this model we found that among carriers of the Met allele , a positive association between executive functioning deficit and number of sexual partners was present. Thus, among Met allele carriers those with greater deficit scores reported greater number of sexual partners; whereas among Val/Val carriers this association was not significant. Similar to results for number of sexual partners, stratified analysis showed that among carriers of the Met/Met but not Val/Met or Val/Val genotype an positive association between executive dysfunction and frequency of insertive anal sex was present, although only statistically significant for models including the Trails B test. Thus, individuals with lower T-scores on Trails B reported greater frequency of insertive anal sex only if they were carriers of the Met/Met genotype. Finally, the strongest interaction observed was between COMT and the Halstead Category Test for frequency of condom use. Contrary to the expected association, results suggest a negative association among carriers of the Met/Met genotype in which lower T-scores on the Category Test was associated with an increased frequency of condom use.