Interactive association of dopamine receptor (DRD4) genotype and ADHD on alcohol expectancies in children

The associations among organophosphate pesticide exposure, oxidative stress, and genetic polymorphisms of paraoxonases in children with attention deficit/hyperactivity disorder

This study will help to clarify the relationship between organophosphate pesticides (OPs) and attention deficit/hyperactivity disorder (ADHD) related to oxidative stress and paraoxonases (PON) polymorphisms to further characterize the gene-environment interaction. This case-control study enrolled 85 children with ADHD and 96 control subjects. Urinary OP levels were analyzed by using gas chromatography-mass spectrometry (GC-MS). Oxidative stress biomarkers, such as 8-hydroxy-2-deoxyguanosine (8-OHdG), 8-nitroguanine (8-NO2-Gua), 8-iso-prostaglandin F2α (8-iso-PGF2α), and 4-hydroxy-2-nonenoic acid-mercapturic acid (HNE-MA), were analyzed by using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The relative excess risk due to interaction (RERI), attributable proportion due to interaction (AP), and synergy index (S) were calculated to evaluate the additive interactions between OP exposure and PON genetic polymorphism on ADHD. A causal mediation analysis was conducted to clarify the mediation effects of oxidative stress due to OP exposure on ADHD. Children with ADHD had significantly higher DMP (238.95 nmol/g cre. vs. 164.83 nmol/g cre., p value = 0.01) and HNE-MA (30.75 μg/g cre. vs. 18.41 μg/g cre., p value<0.01) concentrations than control children. Children who carried the PON1 GG genotype (rs705379) had low urinary DMP levels, and the level increased with increasing numbers of allele variants. The risk for developing ADHD reached 2.06-fold (OR = 2.06, 95% CI:1.23-3.44) and 1.43-fold (OR = 1.45, 95% CI:1.04-2.03) when the DMP and HNE-MA levels increased by 1 natural log of the concentration, respectively. The estimated AP value was 0.66 (95% CI: 0.17-1.15), indicating that 66% of ADHD cases in DMP-exposed children with the PON1 CT/TT (rs705381) genotype were due to gene-environment interactions. No significant mediation of HNE-MA was observed between DMP exposure and the risk of ADHD. The estimated proportion mediated was only 7.0% (95% CI: -0.08-0.46). This research suggests the role of OP exposure in the occurrence of ADHD after adjusting for covariates.

DRD4 48 bp multiallelic variants as age-population-specific biomarkers in attention-deficit/hyperactivity disorder

The identification of biomarkers to support the diagnosis and prediction of treatment response for attention-deficit/hyperactivity disorder (ADHD) is still a challenge. Our previous works highlighted the DRD4 (dopamine receptor D4) as the best potential genetic marker for childhood diagnosis and methylphenidate (MPH) response. Here, we aimed to provide additional evidence on biomarkers for ADHD diagnosis and treatment response, by using more specific approaches such as meta-analytic and bioinformatics tools. Via meta-analytic approaches including over 3000 cases and 16,000 controls, we demonstrated that, among the different variants studied in DRD4 gene, the 48-base pair, Variable Tandem Repeat Polymorphism, VNTR in exon 3 showed an age/population-specificity and an allelic heterogeneity. In particular, the 7R/"long" allele was identified as an ADHD risk factor in European-Caucasian populations (d = 1.31, 95%CI: 1.17-1.47, Z = 4.70/d = 1.36, 95%CI: 1.20-1.55, Z = 4.78, respectively), also, from the results of last meta-analysis, linked to the poor MPH efficacy. The 4R/"short" allele was a protective factor in European-Caucasian and South American populations (d = 0.83, 95%CI: 0.75-0.92, Z = 3.58), and was also associated to positive MPH response. These results refer to children with ADHD. No evidence of such associations was detected for adults with persistent ADHD (data from the last meta-analysis). Moreover, we found evidence that the 4R allele leads to higher receptor expression and increased sensitivity to dopamine, as compared with the 7R allele (d = 1.20, 95%CI: 0.71-1.69, Z = 4.81), and this is consistent with the ADHD protection/susceptibility effects of the respective alleles. Using bioinformatics tools, based on the latest genome-wide association (GWAS) meta-analysis of the Psychiatry Genomic Consortium (PGC), we demonstrated that the 48 bp VNTR is not in Linkage Disequilibrium with the DRD4 SNPs (Single Nucleotide Polymorphisms), which were not found to be associated with ADHD. Moreover, a DRD4 expression downregulation was found in ADHD specific brain regions (Putamen, Z score = -3.02, P = 0.00252). Overall, our results suggest that DRD4 48 bp VNTR variants should be considered as biomarkers to support the diagnosis of ADHD and to predict MPH response, although the accuracy of such a biomarker remains to be further elucidated.

Risky decision-making in children with and without ADHD: A prospective study

Learning from past decisions can enhance successful decision-making. It is unclear whether difficulties in learning from experience may contribute to risky decision-making, which may be altered among individuals with attention-deficit/hyperactivity disorder (ADHD). This study follows 192 children with and without ADHD aged 5 to 10 years for approximately 2.5 years and examines their risky decision-making using the Balloon Emotional Learning Task (BELT), a computerized assessment of sequential risky decision-making in which participants pump up a series of virtual balloons for points. The BELT contains three task conditions: one with a variable explosion point, one with a stable and early explosion point, and one with a stable and late explosion point. These conditions may be learned via experience on the task. Contrary to expectations, ADHD status was not found to be related to greater risk-taking on the BELT, and among younger children ADHD status is in fact associated with reduced risk-taking. In addition, the typically-developing children without ADHD showed significant learning-related gains on both stable task conditions. However, the children with ADHD demonstrated learning on the condition with a stable and early explosion point, but not on the condition with the stable and late explosion point, in which more pumps are required before learning when the balloon will explode. Learning during decision-making may be more difficult for children with ADHD. Because adapting to changing environmental demands requires the use of feedback to guide future behavior, negative outcomes associated with childhood ADHD may partially reflect difficulties in learning from experience.

The interactions among organophosphate pesticide exposure, oxidative stress, and genetic polymorphisms of dopamine receptor D4 increase the risk of attention deficit/hyperactivity disorder in children

OBJECTIVE

The aim of this study was to clarify the association between organophosphate pesticides (OPs) and attention-deficit/hyperactivity disorder (ADHD) related to oxidative stress and genetic polymorphisms.

METHODS

This case-control study enrolled 93 children with ADHD and 112 control children in north Taiwan. Six dialkyl phosphate (DAP) metabolites of OPs and oxidative stress biomarkers were analyzed. Polymorphisms of the dopamine receptor D4 gene (DRD4) were identified.

RESULTS

Children with ADHD had significantly higher dimethylphosphate (DMP, 236.69nmol/g cre. vs. 186.84nmol/g cre., p value = 0.01) and 4-hydroxy-2-nonenal-mercapturic acid (HNE-MA, 28.95µg/g cre. vs. 16.55µg/g cre., p value<0.01) concentrations than control children. Children who carried DRD4 GA/AA genotypes (rs752306) were less likely than those who carried the DRD4 GG genotype to have ADHD (odds ratio [OR]: 0.45, 95% CI: 0.24-0.84). The estimated value of the AP (attributable proportion due to interaction) was 0.59 (95% CI: 0.13-1.05), indicating that 59% of ADHD cases in DMP-exposed children with the DRD4 GG genotype were due to the gene-environment interaction. After adjustment for other covariates, children who carried the DRD4 GG genotype, had been exposed to high DMP levels (more than the median), and had high HNE-MA levels had a significantly increased risk for developing ADHD (OR = 11.74, 95% CI: 2.12-65.04).

CONCLUSION

This study indicated a gene-environment interaction in the risk of ADHD in children. The association between DMP and ADHD in children might relate to the mechanism of lipid peroxidation. Dose-response relationships and the combined effects of OPs, oxidative stress, and genetic polymorphism on ADHD should not be neglected.

Positive alcohol expectancies mediate associations between ADHD behaviors and alcohol-related problems among college students

An increasing percentage of college students report being affected by ADHD behaviors, and this population is at increased risk of experiencing negative consequences associated with alcohol consumption. However, specific factors motivating alcohol consumption and contributing to negative outcomes among these individuals are not well understood. Recent work suggests alcohol expectancies may interact with ADHD behaviors to influence negative drinking-related outcomes among those with elevated inattention and/or hyperactivity-impulsivity. Seven-hundred-forty emerging adults (M age = 19.13 [SD = 2.25] years; 72.1% female; 85.8% Caucasian) enrolled in two public universities in the Southeast and Midwest USA completed the Brief Comprehensive Effects of Alcohol Survey (B-CEOA) and provided self-reports of ADHD symptoms and drinking-related outcomes. Multiple mediation analyses were conducted to evaluate effects of ADHD behaviors (i.e., hyperactivity-impulsivity, and inattention) and related impairment in major life domains (e.g., social interactions, occupational and educational activities, fulfillment of daily responsibilities) on drinking-related outcomes via positive and negative alcohol expectancies, controlling for sex, age, co-occurring oppositional behaviors, and data collection site. Inattention, hyperactivity-impulsivity, and impairment directly predicted both personal and social problems consequent to alcohol use. Effects of ADHD behaviors and impairment on drinking-related personal and social problems were partially mediated by positive expectancies. Findings are consistent with and extend prior work supporting a role of positive alcohol expectancies in alcohol-related negative outcomes among college students experiencing mild to moderate symptoms of ADHD.

Impaired Social Decision-Making Mediates the Association Between ADHD and Social Problems

Attention-deficit/hyperactivity disorder (ADHD) reliably predicts social dysfunction, ranging from poor social competence and elevated peer rejection to inadequate social skills. Yet, the factors mediating predictions of social problems from childhood ADHD are not well understood. In the present study, we investigated social functioning in 186 (69 % male) 6 to 10 year-old (M = 7.88, SD = 1.17) children with (n = 98) and without (n = 87) ADHD who were followed prospectively for two years. We implemented a well-validated measure of social problems as well as a novel social decision-making task assessing dynamic response to changing affective cues at the two-year follow-up. According to separate parent and teacher report, baseline ADHD symptoms positively predicted social problems at the two-year follow-up; individual differences on the social decision-making task mediated this association. This finding was replicated when ADHD dimensions (i.e., inattention and hyperactivity/impulsivity) were separately examined. These findings suggest that the deficient use of affective cues to effectively guide behavior may partially underlie poor social functioning among children with ADHD. If replicated, these preliminary findings suggest that social skills interventions that target interpretation of affective cues to aid in social decision-making behavior may improve social outcomes negatively affected by early ADHD symptoms.

ADHD and Marijuana-Use Expectancies in Young Adulthood

OBJECTIVE

This study examined mean level differences in marijuana expectancies and the differential associations between expectancies and marijuana use for individuals with and without a history of Attention-Deficit/Hyperactivity Disorder (ADHD).

BACKGROUND

Substance-use expectancies are a widely studied risk factor for alcohol and other drug use. The relations between marijuana-use expectancies and self-reported marijuana use have not been examined in young adults with ADHD, a population shown to be at risk for marijuana use.

METHOD

Participants were 306 (190 ADHD and 116 non-ADHD) young adults (M age = 20.06, SD = 2.03) from the Pittsburgh ADHD Longitudinal Study (PALS) who provided data about marijuana use and marijuana-use expectancies.

RESULTS

Individuals in the ADHD group reported lower levels of social enhancement, tension reduction, and cognitive and behavioral-impairment expectancies compared to individuals in the non-ADHD group. Positive and negative marijuana-use expectancies were associated with marijuana use frequency in the whole sample and statistically significant ADHD group by expectancy interactions were found. Sexual-enhancement expectancies were more strongly associated with marijuana use frequency among individuals with ADHD histories while cognitive behavioral-impairment expectancies were more strongly associated with marijuana use frequency among individuals without ADHD.

CONCLUSIONS

Marijuana-use expectancies may be acquired, and operate differently, for individuals with and without ADHD histories. Although future research is needed to test this speculation, these differences may be associated with ADHD-related difficulties in higher order cognitive processes that affect the encoding and utilization of expectations regarding marijuana's effects.

ADHD, impulsivity and alcohol abuse: methods, results, and implications

In this Special Section, the relationships among attention deficit hyperactivity disorder (ADHD), impulsivity, and alcohol abuse are explored by 4 diverse studies. Among these excellent studies, the constructs indicated in the issue title varied in definitions, measurement methods, and interpretive implications. The experimental approaches also varied, including cross-sectional examination of candidate genes in children, determination of long-term outcomes, laboratory tasks to measure attention and inhibition, and alcohol administration. These diverse topics and approaches yielded insights into the etiology and effects of alcohol abuse and indicated research directions that will advance this field.