Seasonality associated with the serotonin 2A receptor -1438 A/G polymorphism

Bipolar II disorder has the highest prevalence of seasonal affective disorder in early-onset mood disorders: Results from a prospective observational cohort study

BACKGROUND

Many mood disorder patients experience seasonal changes in varying degrees. Studies on seasonality have shown that bipolar disorder has a higher prevalence rate in such patients; however, there is limited research on seasonality in early-onset mood disorder patients. This study estimated the prevalence of seasonality in early-onset mood disorder patients, and examined the association between seasonality and mood disorders.

METHODS

Early-onset mood disorder patients (n = 378; 138 major depressive disorder; 101 bipolar I disorder; 139 bipolar II disorder) of the Mood Disorder Cohort Research Consortium and healthy control subjects (n = 235) were assessed for seasonality with Seasonality Pattern Assessment Questionnaire (SPAQ).

RESULTS

A higher global seasonality score, an overall seasonal impairment score, and the prevalence of seasonal affective disorder (SAD) and subsyndromal SAD showed that mood disorder subjects had higher seasonality than the healthy subjects. The former subject group had a significantly higher mean overall seasonal impairment score than the healthy subjects (p < .001); in particular, bipolar II disorder subjects had the highest prevalence of SAD, and the diagnosis of bipolar II disorder had significantly higher odds ratios for SAD when compared to major depression and bipolar I disorder (p < .05).

CONCLUSIONS

Early-onset mood disorders, especially bipolar II disorder, were associated with high seasonality. A thorough assessment of seasonality in early-onset mood disorders may be warranted for more personalized treatment and proactive prevention of mood episodes.

Association of the Serotonin 2A Receptor rs6311 Polymorphism with Diurnal Preference in Koreans

OBJECTIVE

Evidence for the association between circadian rhythm delay and depression is accumulating. Genetic studies have shown that certain polymorphisms in circadian genes are potential genetic markers of diurnal preference. Along with circadian genes, there is a growing interest in other genetic effects on circadian rhythms. This study evaluated whether the HTR2A rs6311 (-1438C/T) polymorphism is associated with diurnal preference in a Korean population.

METHODS

A total of 510 healthy subjects were included in this study. All subjects were genotyped for the HTR2A rs6311 polymorphism and they completed the Korean version of the composite scale of morningness (CSM).

RESULTS

The C allele carriers (C/C+C/T) showed significantly higher CSM scores compared to C allele non-carriers (T/T) (t=2.22, p= 0.03), suggesting the existence of a morning chronotype tendency in C allele carriers. In other words, the T/T genotype may be associated with the evening chronotype.

CONCLUSION

These results suggest that the HTR2A rs6311 polymorphism may be associated with diurnal preference in a healthy Korean population. The absence of the C allele may be responsible for the increasing susceptibility to eveningness in the Korean population. Further studies on HTR2A polymorphisms that evaluate their interactions with various candidate genes and differences in phenotypic expression of polymorphisms according to ethnic groups are warranted to fully understand their association with diurnal preference.

Effect of photoperiodic alterations on depression-like behavior and the brain serotonin system in mice genetically different in tryptophan hydroxylase 2 activity

Reduction of natural illumination in fall/winter months causes seasonal affective disorders (SAD) in vulnerable individuals. Neurotransmitter serotonin (5-HT) is involved in the mechanism of SAD. Tryptophan hydroxylase-2 (TPH2) is the key enzyme of 5-HT synthesis in the brain. C1473 G polymorphism in the Tph2 gene is a key factor defining the enzyme activity in the mouse brain. The main aims of the study were to investigate the effects of C1473 G polymorphism on behavior and brain 5-HT system responses to photoperiod alterations. The experiment was carried out on adult mouse males of B6-1473C and B6-1473 G congenic lines with normal and low TPH2 activities, respectively. B6-1473C and B6-1473 G mice were divided into four groups of 8 each and exposed for 28 days to standard-day (14 h light and 10 h darkness) or short-day (4 h light and 20 h darkness) conditions. No effect of photoperiod on locomotor, exploratory activities and anxiety in the open field test was observed. At the same time, photoperiod alterations affected depressive-like immobility in the forced swim test, the 5-HT, 5-hydroxyindoleacetic acid (5-HIAA) levels, 5-HIAA/5-HT ratio and the Htr2a mRNA level in hippocampus and midbrain. The effect of the interaction between C1473 G polymorphism and photoperiod on 5-HT level and 5-HIAA/5-HT ratio in hippocampus was revealed. Short-day conditions reduced the level and increased 5-HIAA/5-HT ratio in this structure only in B6-1473 G mice. At the same time, C1473 G polymorphism does not alter effects of short-day conditions on immobility time in the forced swim test and the Htr2a mRNA level in the brain.

Stress exposure and psychopathology alter methylation of the serotonin receptor 2A (HTR2A) gene in preschoolers

Serotonin signaling pathways play a key role in brain development, stress reactivity, and mental health. Epigenetic alterations in the serotonin system may underlie the effect of early life stress on psychopathology. The current study examined methylation of the serotonin receptor 2A (HTR2A) gene in a sample of 228 children including 119 with child welfare documentation of moderate to severe maltreatment within the last 6 months. Child protection records, semistructured interviews in the home, and parent reports were used to assess child stress exposure, psychiatric symptoms, and behavior. The HTR2A genotype and methylation of HTR2A were measured at two CpG sites (-1420 and -1224) from saliva DNA. HTR2A genotype was associated with HTR2A methylation at both CpG sites. HTR2A genotype also moderated associations of contextual stress exposure and HTR2A methylation at site -1420. Contextual stress was positively associated with -1420 methylation among A homozygotes, but negatively associated with -1420 methylation among G homozygotes. Posttraumatic stress disorder and major depressive disorder symptoms were negatively associated with methylation at -1420, but positively associated with methylation at -1224. Results support the view that the serotonin system is sensitive to stress exposure and psychopathology, and HTR2A methylation may be a mechanism by which early adversity is biologically encoded.

Genetic Factors Affecting Seasonality, Mood, and the Circadian Clock

In healthy humans, seasonality has been documented in psychological variables, chronotype, sleep, feeding, metabolic and autonomic function, thermoregulation, neurotransmission, and hormonal response to stimulation, thus representing a relevant factor to account for, especially when considering the individual susceptibility to disease. Mood is largely recognized as one of the central aspects of human behavior influenced by seasonal variations. This historical notion, already mentioned in ancient medical reports, has been recently confirmed by fMRI findings, which showed that seasonality in human cognitive brain functions may influence affective control with annual variations. Thus, seasonality plays a major role in mood disorders, affecting psychopathology, and representing the behavioral correlate of a heightened sensitivity to factors influencing circannual rhythms in patients. Although the genetic basis of seasonality and seasonal affective disorder (SAD) has not been established so far, there is growing evidence that factors affecting the biological clock, such as gene polymorphisms of the core clock machinery and seasonal changes of the light-dark cycle, exert a marked influence on the behavior of patients affected by mood disorders. Here we review recent findings about the effects of individual gene variants on seasonality, mood, and psychopathological characteristics.

Association of CLOCK, ARNTL, and NPAS2 gene polymorphisms and seasonal variations in mood and behavior

Seasonal affective disorder (SAD) is a condition of seasonal mood changes characterized by recurrent depression in autumn or winter that spontaneously remits in spring or summer. Evidence has suggested that circadian gene variants contribute to the pathogenesis of SAD. In this study, we investigated polymorphisms in the CLOCK, ARNTL, and NPAS2 genes in relation to seasonal variation in 507 healthy young adults. Seasonal variations were assessed with the Seasonality Pattern Assessment Questionnaire. The prevalence of SAD was 12.0% (winter-type 9.3%, summer-type 2.8%). No significant difference was found between the groups in the genotype distribution of ARNTL rs2278749 and NPAS2 rs2305160. The T allele of CLOCK rs1801260 was significantly more frequent in seasonals (SAD + subsyndromal SAD) compared with non-seasonals (p = 0.020, odds ratio = 1.89, 95% confidence interval = 1.09-3.27). Global seasonality score was significantly different among genotypes of CLOCK rs1801260, but not among genotypes of ARNTL rs2278749 and NPAS2 rs2305160. However, statistical difference was observed in the body weight and appetite subscales among genotypes of ARNTL rs2278749 and in the body weight subscale among genotypes of NPAS2 rs2305160. There was synergistic interaction between CLOCK rs1801260 and ARNTL rs2278749 on seasonality. To our knowledge, this study is the first to reveal an association between the CLOCK gene and seasonal variations in mood and behavior in the Korean population. Although we cannot confirm previous findings of an association between SAD and the ARNTL and NPAS2 genes, these genes may influence seasonal variations through metabolic factors such as body weight and appetite. The interaction of the CLOCK and ARNTL genes contributes to susceptibility for SAD.

Changes in winter depression phenotype correlate with white blood cell gene expression profiles: a combined metagene and gene ontology approach

In the present study we evaluate the feasibility of gene expression in white blood cells as a peripheral marker for winter depression. Sixteen patients with winter type seasonal affective disorder were included in the study. Blood was taken by venous puncture at three time points; in winter prior and following bright light therapy and in summer. RNA was isolated, converted into cRNA, amplified and hybridized on Illumina® gene expression arrays. The raw optical array data were quantile normalized and thereafter analyzed using a metagene approach, based on previously published Affymetrix gene array data. The raw data were also subjected to a secondary analysis focusing on circadian genes and genes involved in serotonergic neurotransmission. Differences between the conditions were analyzed, using analysis of variance on the principal components of the metagene score matrix. After correction for multiple testing no statistically significant differences were found. Another approach uses the correlation between metagene factor weights and the actual expression values, averaged over conditions. When comparing the correlations of winter vs. summer and bright light therapy vs. summer significant changes for several metagenes were found. Subsequent gene ontology analyses (DAVID and GeneTrail) of 5 major metagenes suggest an interaction between brain and white blood cells. The hypothesis driven analysis with a smaller group of genes failed to demonstrate any significant effects. The results from the combined metagene and gene ontology analyses support the idea of communication between brain and white blood cells. Future studies will need a much larger sample size to obtain information at the level of single genes.

Central serotonin-2A (5-HT2A) receptor dysfunction in depression and epilepsy: the missing link?

5-Hydroxytryptamine 2A receptors (5-HT_2A-Rs) are G-protein coupled receptors. In agreement with their location in the brain, they have been implicated not only in various central physiological functions including memory, sleep, nociception, eating and reward behaviors, but also in many neuropsychiatric disorders. Interestingly, a bidirectional link between depression and epilepsy is suspected since patients with depression and especially suicide attempters have an increased seizure risk, while a significant percentage of epileptic patients suffer from depression. Such epidemiological data led us to hypothesize that both pathologies may share common anatomical and neurobiological alteration of the 5-HT_2A signaling. After a brief presentation of the pharmacological properties of the 5-HT_2A-Rs, this review illustrates how these receptors may directly or indirectly control neuronal excitability in most networks involved in depression and epilepsy through interactions with the monoaminergic, GABAergic and glutamatergic neurotransmissions. It also synthetizes the preclinical and clinical evidence demonstrating the role of these receptors in antidepressant and antiepileptic responses.

Prevalence, behavioral manifestations and associated individual and climatic factors of seasonality in the Korean general population

BACKGROUNDS

Seasonality, an individual trait of seasonal variations in mood and behavior, has received clinical attention for its association with mood disorders. This study aimed to explore the prevalence, specific manifestation, and associated individual and climatic factors of seasonality in the non-elderly adult population.

METHODS

Five hundred fifty-two participants [male n=220; female n=332; mean age 34.92years, standard deviation (SD) 10.18] with no psychiatric history were recruited from the Seoul metropolitan area (37°33'58.87″N 126°58'40.63″E). Seasonality was evaluated using the Seasonal Pattern Assessment Questionnaire. Climatic variables used in analyses were averaged over recent 5years (from 2008 to 2013) on a monthly basis.

RESULTS

The mean global seasonality score (GSS) was 5.53 (SD 3.91), and 16.2% (n=89) of participants had seasonal affective disorder (SAD) or sub-SAD. The "feeling worst" month in most of the participants with significant seasonality were winter (41.6%) or summer (38.2%). Socio-demographic factors including age and sex were not related to the seasonality. Decreased sunlight amount and diurnal temperature range in a given and previous month, and increased humidity in a previous month showed significant associations with the percentage of participants with the worst mood. The most frequently reported symptom related to seasonality was 'changes in energy level'. Specific manifestations were not significantly different between the winter type and the summer type.

CONCLUSION

The summer and winter type seasonality in the non-clinical adult population did not differ in terms of behavioral manifestations. Decreased sunlight amount, diurnal temperature range, and increased humidity appeared to be major climatic factors associated with seasonality.

Converging translational evidence for the involvement of the serotonin 2A receptor gene in major depressive disorder

An association between serotonin 2A receptor (5-HT2AR), encoded by HTR2A gene, and major depressive disorder (MDD) has been suggested. Here, we combined preclinical and ecological clinical approaches to explore the impact of impaired 5-HT2AR-mediated transmission on MDD or anxio-depressive-like phenotype in mice. Htr2a knock-out mice (Htr2a(-/-)) and wild-type mice were compared for the ability of chronic corticosterone to elicit some anxio-depressive-like phenotype in three behavioral paradigms (elevated plus maze, tail suspension test and splash test). Accordingly, two single nucleotide polymorphisms of the HTR2A gene (rs6314 ie His452Tyr and rs6313 ie 102C/T), which specific allelic variants may decrease 5-HT2AR-mediated transmission (as in Htr2a(-/-)mice), were studied in a sample of 485 Caucasian patients with MDD. In response to chronic corticosterone exposure, Htr2a(-/-) mice displayed more pronounced anxiodepressive-like phenotype than wild-type mice, as shown by a significant higher "emotionality score" (p<0.01). In patients, the C allele of rs6313 was more frequent in depressed patients (p=0.019) and was also associated with a more severe major depressive episode (p=0.03). This translational and ecological study involving constitutive Htr2a(-/-) knock-out mice and related SNPs in depressed patients suggests that a lower neurotransmission at the 5-HT2AR may favor the susceptibility and severity of MDE. It also suggests that specific allelic variants of the rs6313 and rs6314 may reduce 5-HT2AR-mediated transmission.

Interactions of the serotonin and circadian systems: nature and nurture in rhythms and blues

The serotonin and circadian systems are principal regulatory networks of the brain. Each consists of a unique set of neurons that make widespread neural connections and a defined gene network of transcriptional regulators and signaling genes that subserve serotonergic and circadian function at the genetic level. These master regulatory networks of the brain are extensively intertwined, with reciprocal circuit connections, expression of key genetic elements for serotonin signaling in clock neurons and expression of key clock genes in serotonergic neurons. The reciprocal connections of the serotonin and circadian systems likely have importance for neurobehavioral disorders, as suggested by their convergent contribution to a similar range of mood disorders including seasonal affective disorder (SAD), bipolar disorder, and major depression, and as suggested by their overlapping relationship with the developmental disorder, autism spectrum disorder. Here we review the neuroanatomical and genetic basis for serotonin-circadian interactions in the brain, their potential relationship with neurobehavioral disorders, and recent work examining the effects on the circadian system of genetic perturbation of the serotonergic system as well as the molecular and behavioral effects of developmental imprinting of the circadian system with perinatal seasonal light cycles.

Seasonality and winter-type seasonal depression are associated with the rs731779 polymorphism of the serotonin-2A receptor gene

Seasonal Affective Disorder (SAD), seasonality and increased sensitivity to the fluctuation of seasons in biological and psychological parameters can manifest to varying degrees across a normal population. The serotonin-2A (5-HT2A) receptor gene has long been suggested as a candidate for the genetic basis of this phenomenon. We hypothesized that functional sequence variation in this gene could contribute to seasonality and the development of winter- and/or summer-type seasonal depression. Seasonality was measured by the self-rating Global Seasonality Score (GSS) of the Seasonal Pattern Assessment Questionnaire, and SAD by the Seasonal Health Questionnaire (SHQ). We analysed associations between GSS or SAD scores and 5-HTR2A receptor gene polymorphisms rs731779, rs985934 and rs6311, in 609 individuals. People carrying the GG genotype of rs731779 were six times more likely to manifest winter or summer SAD compared to GT or TT genotypes (OR = 6.47), and the chance of having winter-type SAD was almost nine-fold (OR = 8.7) with the GG genotype. GG subjects of rs731779 also scored significantly higher on the GSS scale compared to carriers of the T allele. In the haplotype analysis subjects carrying the G allele of rs731779 scored higher on the GSS scale, while the presence of the T allele leads to lower scores. These results suggest that variations in the 5-HTR2A gene play a significant role in the development of seasonality and especially in winter-type SAD. The fact that the above polymorphism showed association not only with clinical SAD but also seasonality symptoms in a general population provides evidence for the spectrum nature of this connection.

Cultural variation in seasonal depression: cross-national differences in winter versus summer patterns of seasonal affective disorder

BACKGROUND

Research suggests that two dimensions of national culture, individualism-collectivism and power distance, predict affective responses to the seasonally varying levels of ambient sunlight that may underlie regular cycles of mood and behavior in Seasonal Affective Disorder (SAD). Specifically, negative affect is predicted by the diminished sunlight of fall-winter in countries higher in individualism and lower in power distance, and by the increased sunlight of spring-summer in countries lower in individualism and higher in power distance. This study tests whether individualism correlates positively, and power distance negatively, with the frequency of winter-SAD relative to that of summer-SAD.

METHOD

A search for studies reporting frequencies of both winter-SAD and summer-SAD identified 55 samples encompassing 18 countries and 38,408 participants, including 1931 with SAD.

RESULTS

The frequency of winter-SAD, relative to that of summer-SAD, correlated positively with individualism (r=.67, p=.001) and negatively with power distance (r=-.72, p=.0001). Countries in which winter-SAD was more common than summer-SAD were significantly more individualistic and less power-distant than countries in which summer-SAD was more common than winter-SAD. Results survived various tests of threats to validity.

LIMITATIONS

The study is limited by the quantity, quality, diversity, and representativeness of the research under review and by its correlational design.

CONCLUSIONS

Individualism and power distance are strongly related to the relative prevalence of winter-SAD and summer-SAD. Culture may play an important but previously overlooked role in the etiology of SAD.

A missense variant (P10L) of the melanopsin (OPN4) gene in seasonal affective disorder

BACKGROUND

Melanopsin, a non-visual photopigment, may play a role in aberrant responses to low winter light levels in Seasonal Affective Disorder (SAD). We hypothesize that functional sequence variation in the melanopsin gene could contribute to increasing the light needed for normal functioning during winter in SAD.

METHODS

Associations between alleles, genotypes, and haplotypes of melanopsin in SAD participants (n=130) were performed relative to controls with no history of psychopathology (n=90).

RESULTS

SAD participants had a higher frequency of the homozygous minor genotype (T/T) for the missense variant rs2675703 (P10L) than controls, compared to the combined frequencies of C/C and C/T. Individuals with the T/T genotype were 5.6 times more likely to be in the SAD group than the control group, and all 7 (5%) of individuals with the T/T genotype at P10L were in the SAD group.

LIMITATIONS

The study examined only one molecular component of the non-visual light input pathway, and recruitment methods for the comparison groups differed.

CONCLUSION

These findings support the hypothesis that melanopsin variants may predispose some individuals to SAD. Characterizing the genetic basis for deficits in the non-visual light input pathway has the potential to define mechanisms underlying the pathological response to light in SAD, which may improve treatment.

Association Study of a Serotonin Receptor 2A Gene -1438A/G Polymorphism and Anxiety-Related Traits

OBJECTIVE

The aim of this study was to investigate the relationship between the -1438A/G polymorphism of serotonin receptor 2A (5HTR2A) and anxiety-related traits in Korean adolescent females.

METHODS

A total of 174 Korean adolescent females were tested for the -1438A/G polymorphism of 5HTR2A using polymerase chain reaction (PCR)-based methods. Anxiety-related traits were evaluated using the Anxiety Sensitivity Index (ASI) and the trait form of the Spielberg State-Trait Anxiety Inventory (T-STAI).

RESULTS

There was no difference between the genotypes with respect to scores pertaining to anxiety-related traits. Although the G allele carriers (GG or AG genotype) scored lower on the psychological subscale of the ASI (4.76+/-3.00 vs 5.98+/-4.00, p=0.038), this difference was not significant after Bonferroni correction.

CONCLUSION

These findings suggest that the -1438A/G polymorphism of 5HTR2A might not be associated with anxiety sensitivity or trait anxiety.

Genetic variability at HPA axis in major depression and clinical response to antidepressant treatment

BACKGROUND

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis has been observed in major depression. Normalization of HPA axis has been suggested to play a role in the mechanisms of action of antidepressants. Our aim was to investigate the influence of genetic variants in CRHR1, CRHR2, CRH-BP and FKBP5 genes on both the vulnerability for depression and the response to antidepressant treatment.

METHODS

The sample consisted of 159 depressive outpatients and 96 healthy controls of Spanish origin. Patients were assessed for clinical features including, among others, age of onset, seasonality or suicidal behavior. The episode was treated with citalopram and followed along 12 weeks. Severity of symptoms was evaluated at the inclusion and then monthly along the follow-up using a 21-item Hamilton Depression Rating Score (HDRS). SNPs were assayed using Applied Biosystems SNaP-Shot and TaqMan technology.

RESULTS

rs110402, in CRHR1 gene, was associated with an increased risk to present a seasonal pattern and an early age of onset of the first depressive episode. Allele G carriers of rs2270007 of CRHR2 gene, showed a worse overall response to citalopram along time of follow-up (Genotype effect F=7.45, P=0.007). G allele carriers showed 2.93 increased risk (95% CI [1.24-6.90]) for non-responding at 4th week to citalopram treatment (chi(2)=7.59, df=1, P=0.006).

LIMITATIONS

On the light of the moderate sample size, associations based on the mentioned polymorphisms need to be considered with caution and require further replication studies in other samples.

CONCLUSIONS

Variability at genes encoding proteins with a pivotal role in HPA axis regulation seems to influence i) the expression of severity variables of the depressive spectrum including early age of onset or a seasonal pattern and ii) the interindividual variation in clinical response to SSRI antidepressants.