2015

The catecholamines dopamine and noradrenaline have been implicated in spontaneous low-frequency fluctuations in reaction time, which are associated with attention deficit hyperactivity disorder (ADHD) and subclinical attentional problems. The molecular genetic substrates of these behavioral phenotypes, which reflect frequency ranges of intrinsic neuronal oscillations (Slow-4: 0.027-0.073 Hz; Slow-5: 0.010-0.027 Hz), have not yet been investigated. In this study, we performed regression analyses with an additive model to examine associations between low-frequency fluctuations in reaction time during a sustained attention task and genetic markers across 23 autosomal catecholamine genes in a large young adult population cohort (n = 964), which yielded greater than 80% power to detect a small effect size (f(2) = 0.02) and 100% power to detect a small/medium effect size (f(2) = 0.15). At significance levels corrected for multiple comparisons, none of the gene variants were associated with the magnitude of low-frequency fluctuations. Given the study's strong statistical power and dense coverage of the catecholamine genes, this either indicates that associations between low-frequency fluctuation measures and catecholamine gene variants are absent or that they are of very small effect size. Nominally significant associations were observed between variations in the alpha-2A adrenergic receptor gene (ADRA2A) and the Slow-5 band. This is in line with previous reports of an association between ADRA2A gene variants and general reaction time variability during response selection tasks, but the specific association of these gene variants and low-frequency fluctuations requires further confirmation. Pharmacological challenge studies could in the future provide convergent evidence for the noradrenergic modulation of both general and time sensitive measures of intra-individual variability in reaction time.

Background. The relationship between early adverse life events and later internalizing problems could be mediated by DNA methylation. Adversity has been associated with higher methylation levels in the glucocorticoid receptor gene (NR3C1) and the serotonin transporter gene (SLC6A4) in adolescents. We investigated cross-sectional and prospective associations of NR3C1 and SLC6A4 methylation with adolescents׳ clinical diagnoses of internalizing disorders and internalizing symptom scores. Methods. In a population sample (mean age=16.2) we measured DNA methylation in three regions of NR3C1 (NR3C1_1, N=454; NR3C1_2, N=904; NR3C1_3, N=412) and one region of SLC6A4 (N=939) at baseline. Internalizing problems were operationalized as clinical DSM-IV diagnoses, assessed at 3 year follow-up with a diagnostic interview, and internalizing symptom scores, assessed with Self-Report questionnaires at baseline and follow-up. Results. Only NR3C1_1 methylation was positively associated with risk of lifetime internalizing disorders, and with symptom scores at follow-up. However, after accounting for baseline symptom scores there was only a tendency for association with internalizing symptom scores at follow-up. There was no association between SLC6A4 methylation and risk of lifetime internalizing disorders. SLC6A4 methylation and internalizing symptom scores showed a tendency for association, also after accounting for baseline symptom scores. Limitations. There was no repeated measure of DNA methylation to study causality between methylation and internalizing problems. Gene expression data were not available. Conclusions. Although the role of gene methylation in the development of internalizing problems remains unclear, our findings suggest that gene methylation, particularly of NR3C1, may be involved in the development of internalizing problems in adolescence.

Copyright © 2015 Elsevier B.V. All rights reserved.

Early life adversity and psychopathology are thought to be linked through HPA-axis deregulation. Changes in methylation levels of stress reactivity genes such as the glucocorticoid receptor gene (NR3C1) can be induced by adversity. Higher NR3C1 methylation levels have been associated with a reduced NR3C1 expression, possibly leading to impaired negative feedback regulation of the HPA-axis. In this study we tested whether methylation levels of NR3C1 were associated with HPA-axis regulation, operationalized as cortisol responses. In 361 adolescents (mean age 16.1, SD = 0.6), salivary cortisol samples were collected before, during, and after a social stress task, from which response measures (cortisol activation and recovery) were calculated. Higher NR3C1 methylation levels were associated with a flattened cortisol recovery slope, indicating a delayed recovery time. Cortisol response activation was not associated with NR3C1 methylation. These results suggest that methylation of NR3C1 may impair negative feedback of the HPA-axis in adolescents.