Association study between a polymorphism at the 3'-untranslated region of CLOCK gene and attention deficit hyperactivity disorder

The circadian system: A neglected player in neurodevelopmental disorders

Patients with neurodevelopmental disorders, such as autism spectrum disorder, often display abnormal circadian rhythms. The role of the circadian system in these disorders has gained considerable attention over the last decades. Yet, it remains largely unknown how these disruptions occur and to what extent they contribute to the disorders' development. In this review, we examine circadian system dysregulation as observed in patients and animal models of neurodevelopmental disorders. Second, we explore whether circadian rhythm disruptions constitute a risk factor for neurodevelopmental disorders from studies in humans and model organisms. Lastly, we focus on the impact of psychiatric medications on circadian rhythms and the potential benefits of chronotherapy. The literature reveals that patients with neurodevelopmental disorders display altered sleep-wake cycles and melatonin rhythms/levels in a heterogeneous manner, and model organisms used to study these disorders appear to support that circadian dysfunction may be an inherent characteristic of neurodevelopmental disorders. Furthermore, the pre-clinical and clinical evidence indicates that circadian disruption at the environmental and genetic levels may contribute to the behavioural changes observed in these disorders. Finally, studies suggest that psychiatric medications, particularly those prescribed for attention-deficit/hyperactivity disorder and schizophrenia, can have direct effects on the circadian system and that chronotherapy may be leveraged to offset some of these side effects. This review highlights that circadian system dysfunction is likely a core pathological feature of neurodevelopmental disorders and that further research is required to elucidate this relationship.

Evaluation of the Regulatory Role of Circadian Rhythm Related Long Non-Coding RNAs in ADHD Etiogenesis

OBJECTIVE

ADHD is associated with increased sleep problems and circadian rhythm disturbances. This study aimed to examine ADHD patients and healthy controls in terms of chronotypic features and expression levels of CLOCK, PER1, lncRNA HULC, lncRNA UCA1.

METHOD

Eighty-three children were included (43 ADHD). Conner's Parent Rating Scale-Revised Short Form, Childhood Chronotype Questionnaire, Children's Sleep Disorders Scale were administered. Gene expression levels were studied from peripheral blood.

RESULTS

Evening chronotype, sleep initiation/maintenance disorder, sleep-wake transition disorder, excessive sleepiness disorder were higher in the ADHD group compared to the controls in the scales reported by the parents. Expression levels of all examined genes were statistically significantly higher in the ADHD group. There was no significant relationship between genes and sleep parameters in the ADHD group.

CONCLUSION

Our study provides the first evidence that lncRNA HULC and lncRNA UCA1 might have a role in the etiology of ADHD.

Association between CLOCK gene polymorphisms and ADHD in Mexican teenagers: A comprehensive assessment

This study aimed to evaluate markers of the CLOCK gene rs1801260 and rs4864548 in Mexican adolescents, addressing clinical and biological aspects previously associated with ADHD. 347 Mexican adolescents were assessed for mental disorders, metabolic disruption and related conditions, circadian preference, as well as genotyping for the CLOCK. We found a significant association between ADHD and the AA and AG genotypes of rs1801260. Also, we identified in the ADHD group that the total Triiodothyronine and total Thyroxine values were respectively 10 ng/dl units and 0.58 ug/dl units lower in females than in males. Previously reported common variations of the CLOCK gene have been associated with ADHD like the Rs1801260 polymorphism hereby we could consider it as risk factor, but genetic, biochemical and clinical studies in the Mexican population are entailed.

Krüppel-like factor 7 deficiency causes autistic-like behavior in mice via regulating Clock gene

BACKGROUND

Krüppel-like factor 7 (klf7), a transcription factor in the nervous system to regulate cell proliferation and differentiation, has been recently identified as a causal gene for autism spectrum disorder (ASD), but the mechanism behind remains unknown.

RESULT

To uncover this mechanism, in this study we characterized the involvement of klf7 in circadian rhythm by knocking down klf7 in N2A cells and examining the rhythmic expression of circadian genes, especially Clock gene. We constructed klf7^-/- mice and then investigated into klf7 regulation on the expression of rhythm genes in vivo as well as the use of melatonin to rescue the autism behavior. Our results illustrated that circadian rhythm was disrupted in klf7 knockdown cells and that klf7^-/- mice showed autism-like behavior. Also, we found that Clock gene was downregulated in the brain of these klf7^-/- mice and that the downstream rhythm genes of Clock were disturbed. Melatonin, as a circadian regulation drug, could regulate the expression level and amplitude of rhythm genes in klf7 knockout cells and further rescue the autistic behavior of klf7^-/- mice.

CONCLUSION

Klf7 deficiency causes ASD by disrupting circadian rhythm related genes to trigger rhythm oscillations. To treat ASD, maintaining circadian homeostasis is promising with the use of melatonin.

Clock Genes Profiles as Diagnostic Tool in (Childhood) ADHD—A Pilot Study

Attention deficit hyperactivity disorder (ADHD) is a very common disorder in children and adults. A connection with sleep disorders, and above all, disorders of the circadian rhythm are the subject of research and debate. The circadian system can be represented on different levels. There have been a variety of studies examining 24-h rhythms at the behavioral and endocrine level. At the molecular level, these rhythms are based on a series of feedback loops of core clock genes and proteins. In this paper, we compared the circadian rhythms at the behavioral, endocrine, and molecular levels between children with ADHD and age- and BMI-matched controls, complementing the previous data in adults. In a minimally invasive setting, sleep was assessed via a questionnaire, actigraphy was used to determine the motor activity and light exposure, saliva samples were taken to assess the 24-h profiles of cortisol and melatonin, and buccal mucosa swaps were taken to assess the expression of the clock genes BMAL1 and PER2. We found significant group differences in sleep onset and sleep duration, cortisol secretion profiles, and in the expression of both clock genes. Our data suggest that the analysis of circadian molecular rhythms may provide a new approach for diagnosing ADHD in children and adults.

Timing is everything: Circadian rhythms and their role in the control of sleep

Sleep and the circadian clock are intertwined and have persisted throughout history. The suprachiasmatic nucleus (SCN) orchestrates sleep by controlling circadian (Process C) and homeostatic (Process S) activities. As a "hand" on the endogenous circadian clock, melatonin is critical for sleep regulation. Light serves as a cue for sleep/wake control by activating retino-recipient cells in the SCN and subsequently suppressing melatonin. Clock genes are the molecular timekeepers that keep the 24 h cycle in place. Two main sleep and behavioural disorder diagnostic manuals have now officially recognised the importance of these processes for human health and well-being. The body's ability to respond to daily demands with the least amount of effort is maximised by carefully timing and integrating all components of sleep and waking. In the brain, the organization of timing is essential for optimal brain physiology.

Relationship between sleep problems and chronotypes of children and adolescents with attention deficit and hyperactivity disorder and serum GABA, glutamate and homocysteine levels

In this study, we aimed to determine the relationship between chronotype, sleep problems and serum levels of GABA (gamma amminobutyric acid), glutamate and homocysteine in children and adolescents diagnosed with attention deficit and hyperactivity disorder (ADHD) as well as factors affecting this relationship. Sleep problems of 46 children and adolescents aged 7-18 years diagnosed with ADHD and 30 healthy volunteers aged 7-18 years were evaluated with Children's Sleep Habits Questionnaire (CSHQ) while chronotypes were evaluated with Children's Chronotype Questionnaire (CCQ). Serum glutamate, GABA and homocysteine levels were measured using immunosorbent test (ELISA) kits. Sleep problems were significantly more common in the ADHD group compared to the control group (p < .001). Serum GABA, glutamate and homocysteine levels were found to be predictor biomarkers for ADHD, independent of total sleep problem score. When the homocysteine levels were above the cut-off point of 9.445 µmol/L, the sensitivity in early diagnosis of ADHD was 84.8% and the specificity was 70.0%. Although ADHD is a disorder in which sleep problems are common, increased serum GABA, glutamate and homocysteine are important in diagnosing ADHD independent of ADHD-related sleep problems. Homocysteine levels may be an important predictor for the presence of ADHD.

Sleep-related traits and attention-deficit/hyperactivity disorder comorbidity: Shared genetic risk factors, molecular mechanisms, and causal effects

OBJECTIVES

To evaluate the shared genetic components, common pathways and causal relationship between ADHD and sleep-related phenotypes.

METHODS

We used the largest genome-wide association summary statistics available for attention-deficit/hyperactivity disorder (ADHD) and various sleep-related phenotypes (insomnia, napping, daytime dozing, snoring, ease getting up, daytime sleepiness, sleep duration and chronotype). We estimated the genomic correlation using cross-trait linkage disequilibrium score regression (LDSR) and investigated the potential common mechanisms using gene-based cross-trait metanalyses and functional enrichment analyses. The causal effect was estimated using two-sample Mendelian randomisation (TSMR), using the inverse variance weighted method as the main estimator.

RESULTS

A positive genomic correlation between insomnia, daytime napping, daytime dozing, snoring, daytime sleepiness, short and long sleep duration, and ADHD was observed. Insomnia, daytime sleepiness, and snoring shared genes with ADHD, that are involved in neurobiological functions and regulatory signalling pathways. The TSMR supported a causal effect of insomnia, daytime napping, and short sleep duration on ADHD, and of ADHD on long sleep duration and chronotype.

CONCLUSION

Comorbidity between sleep phenotypes and ADHD may be mediated by common genetic factors that play an important role in neuronal signalling pathways. A causal effect of sleep disturbances and short sleep duration on ADHD reinforced their role as predictors of ADHD.

For whom the circadian clock ticks? Investigation of PERIOD and CLOCK gene variants in bipolar disorder

Clock genes play significant roles in the regulation of circadian rhythms, which are thought to be involved in the pathophysiology of neurodegenerative and psychiatric diseases. We aimed to investigate the association of five gene polymorphisms (PER3 VNTR (rs57875989), PER2 rs2304672, CLOCK rs1801260, CLOCK rs10462028, CLOCK rs11932595) with PCR-based methods as potential risk factors in bipolar disorder (BD). We used a multiple testing methodology in BD patients (n = 121) and healthy control individuals (n = 121) of Turkish descent to analyze the effects of these gene variants both as risk factors for the disorder and for the evaluation of these variants in the patient group with multiple subscales. We evaluated the circadian rhythm disturbances and seasonal variations in mood and behavior in BD patients using the Biological Rhythms Interview of Assessment in Neuropsychiatry (BRIAN) and Seasonal Pattern Assessment Questionnaire (SPAQ) to enlighten the possible links between these scores and the studied circadian gene variants. The results of our study revealed significant associations: PER3 VNTR (rs57875989) 5/5 repeat genotype displayed a protective effect against BD when compared with 4/4 repeat genotype. Moreover, patients with PER3 VNTR 5/5 repeat genotype displayed a higher ratio of hypomania. PER2 rs2304672 G allele frequency increased the risk for BD. There was no association in terms of genotype/allele frequency comparisons between patients and controls for CLOCK gene variants. However, significant associations were found in patients in terms of clinical and behavioral patterns such as mean age at disease onset and BRIAN total scores enabling some risk stratifications for patients. Our results indicate the significance of circadian gene variants in BD, which need to be confirmed in different studies with larger samples. Thus, the possible endophenotypes of BD can be enlightened and advanced chronotherapeutics approaches can be manipulated in the future for clinical benefit.

Current Evidence on the Role of the Gut Microbiome in ADHD Pathophysiology and Therapeutic Implications

Studies suggest that the bidirectional relationship existent between the gut microbiome (GM) and the central nervous system (CNS), or so-called the microbiome–gut–brain axis (MGBA), is involved in diverse neuropsychiatric diseases in children and adults. In pediatric age, most studies have focused on patients with autism. However, evidence of the role played by the MGBA in attention deficit/hyperactivity disorder (ADHD), the most common neurodevelopmental disorder in childhood, is still scanty and heterogeneous. This review aims to provide the current evidence on the functioning of the MGBA in pediatric patients with ADHD and the specific role of omega-3 polyunsaturated fatty acids (ω-3 PUFAs) in this interaction, as well as the potential of the GM as a therapeutic target for ADHD. We will explore: (1) the diverse communication pathways between the GM and the CNS; (2) changes in the GM composition in children and adolescents with ADHD and association with ADHD pathophysiology; (3) influence of the GM on the ω-3 PUFA imbalance characteristically found in ADHD; (4) interaction between the GM and circadian rhythm regulation, as sleep disorders are frequently comorbid with ADHD; (5) finally, we will evaluate the most recent studies on the use of probiotics in pediatric patients with ADHD.

The Role of the Circadian System in Attention Deficit Hyperactivity Disorder

Attention deficit hyperactivity disorder (ADHD) is a common neurodevelopmental condition characterised by the core symptoms of inattention, impulsivity and hyperactivity. Similar to many other neuropsychiatric conditions, ADHD is associated with very high levels of sleep disturbance. However, it is not clear whether such sleep disturbances are precursors to, or symptoms of, ADHD. Neither is it clear through which mechanisms sleep and ADHD are linked. One possible link is via modulation of circadian rhythms. In this chapter we overview the evidence that ADHD is associated with alterations in circadian processes, manifesting as later chronotype and delayed sleep phase in ADHD, and examine some mechanisms that may lead to such changes. We also interrogate how the circadian clock may be a substrate for therapeutic intervention in ADHD (chronotherapy) and highlight important new questions to be addressed to move the field forward.

[Adult attention deficit hyperactivity disorder and comorbidity: new findings on epidemiological and genetic factors]

All large population-based administrative studies currently indicate a significant comorbidity of adult attention deficit hyperactivity disorder (ADHD) with addictive, anxiety and in particular affective disorders. In these investigations the risk for one of these comorbid disorders increased with increasing age of the ADHD patients. The most recent genome-wide association and correlation studies also revealed indications for joint genetic risk factors of ADHD with, in particular unipolar depression, bipolar disorder, autism spectrum disorders, Tourette's syndrome and to a lesser extent schizophrenia. The only psychiatric disorder that was negatively correlated with ADHD was anorexia nervosa. Additionally, cannabis and cocaine use were significantly positively genetically correlated with ADHD. Furthermore, an increased occurrence of some specific somatic diseases could be found in patients with adult ADHD. In particular, obesity, migraine, sleep disorders, asthma and celiac disease showed a significantly positive association with ADHD in several studies. No association was found between ADHD and cardiovascular disease. Here as well there are initial indications of joint genetic risk variants; however, data are still sparse and additional studies are needed before valid conclusions can be drawn. To some extent these associated somatic diseases might be differential diagnoses rather than true comorbidities, for example, obstructive sleep apnea syndrome (OSAS) can lead to ADHD-like symptoms that disappear when the OSAS is sufficiently treated. Therefore, it is important to keep the co-occurrence of psychiatric and somatic disorders in mind during the diagnostics and treatment of adult ADHD patients to improve their general health and quality of life.

Sleep and Microbiome in Psychiatric Diseases

Objectives: Disturbances in the gut–brain barrier play an essential role in the development of mental disorders. There is considerable evidence showing that the gut microbiome not only affects digestive, metabolic and immune functions of the host but also regulates host sleep and mental states through the microbiota–gut–brain axis. The present review summarizes the role of the gut microbiome in the context of circadian rhythms, nutrition and sleep in psychiatric disorders. Methods: A PubMed search (studies published between April 2015–April 2020) was conducted with the keywords: “sleep, microbiome and psychiatry”; “sleep, microbiome and depression”; “sleep, microbiome and bipolar disorder”, “sleep, microbiome and schizophrenia”, “sleep, microbiome and anorexia nervosa”, “sleep, microbiome and substance use disorder”, “sleep, microbiome and anxiety”; “clock gene expression and microbiome”, “clock gene expression and nutrition”. Only studies investigating the relationship between sleep and microbiome in psychiatric patients were included in the review. Results: Search results yielded two cross-sectional studies analyzing sleep and gut microbiome in 154 individuals with bipolar disorder and one interventional study analyzing the effect of fecal microbiota transplantation in 17 individuals with irritable bowel syndrome on sleep. In patients with bipolar disorder, Faecalibacterium was significantly associated with improved sleep quality scores and a significant correlation between Lactobacillus counts and sleep. Conclusion: Translational research on this important field is limited and further investigation of the bidirectional pathways on sleep and the gut microbiome in mood disorders is warranted.

Polymorphic Appetite Effects on Waist Circumference Depend on rs3749474 CLOCK Gene Variant

Chronobiological aspects controlled by CLOCK genes may influence obesity incidence. Although there are studies that show an association between the expression of these genes and energy intake, waist circumference or abdominal obesity phenotypes, interactions with appetite have been insufficiently investigated in relation to chrononutrition. The objective was to identify interactions between CLOCK genetic variants involved in appetite status. A total of 442 subjects (329 women, 113 men; aged 18 to 65 years) were recruited. Anthropometric, dietary and lifestyle data were collected by trained nutritionists. Participants were classified according to their appetite feelings with a Likert scale. Multiple linear regression models were used to examine associations of the type genotype x appetite status on adiposity-related variables. p values were corrected by the Bonferroni method. A significant influence was found concerning the effects of appetite on waist circumference with respect to rs3749474 CLOCK polymorphism (p < 0.001). An additive model analysis (adjusted by age, gender, exercise and energy intake) showed that risk allele carriers, increased the waist circumference around 14 cm (β = 14.1, CI = 6.3-22.0) by each increment in the level of appetite. The effects of appetite on waist circumference may be partly modulated by the rs3749474 CLOCK polymorphism.

The potential role of clock genes in children attention-deficit/hyperactivity disorder

BACKGROUND

Attention deficit/ hyperactivity disorder (ADHD) is a chronic neurodevelopmental disorder and is thought to be associated with circadian system.

METHODS

We performed a pathway-based study to test individual single nucleotide polymorphisms (SNPs) and the overall evidence of genetic polymorphisms involved in the circadian pathway in association with children ADHD susceptibility among a Chinese population. A community-based case-control study was conducted among Chinese children, and 168 ADHD patients and 233 controls were recruited using a combination diagnosis based on the diagnostic and statistical manual of mental disorders iv (DSM-IV) ADHD rating scale, Swanson, Nolan, and Pelham rating scale (SNAP-IV) rating scale, and semi-structured clinical interview.

RESULTS

The results of single-loci analyses identified that PER1 rs2518023 and ARNTL2 rs2306074 were nominally association with ADHD susceptibility (P < 0.05). Next, we applied multifactor dimensionality reduction (MDR), and classification and regression tree (CART) analyses to explore high-order gene-gene interactions among the functional SNPs to ADHD risks. The results indicated that interactions among the PER1 rs2518023, ARNTL2 rs2306074 and NR1D1 rs939347 were associated with the risk of ADHD in children. Individuals carrying the combination genotypes of the PER1 rs2518023 GG or GT, ARNTL2 rs2306074 TC or TT and NR1D1 rs939347 GA or AA displayed a significantly higher risk for ADHD than who carry the PER1 rs2518023 TT and CRY2 rs2292910 CA/CC genotypes (adjusted OR = 4.37, 95% CI = 2.16-8.85, P < 0.001).

CONCLUSIONS

These findings revealed the importance of genetic variations related to the circadian clock system to the susceptibility of children ADHD.

ADHD 24/7: Circadian clock genes, chronotherapy and sleep/wake cycle insufficiencies in ADHD

Objectives: The current paper addresses the evidence for circadian clock characteristics associated with attention-deficit hyperactivity disorder (ADHD), and possible therapeutic approaches based on chronomodulation through bright light (BL) therapy.Methods: We review the data reported in ADHD on genetic risk factors for phase-delayed circadian rhythms and on the role of photic input in circadian re-alignment.Results: Single nucleotide polymorphisms in circadian genes were recently associated with core ADHD symptoms, increased evening-orientation and frequent sleep problems. Additionally, alterations in exposure and response to photic input may underlie circadian problems in ADHD. BL therapy was shown to be effective for re-alignment of circadian physiology toward morningness, reducing sleep disturbances and bringing overall improvement in ADHD symptoms. The susceptibility of the circadian system to phase shift by timed BL exposure may have broad cost-effective potential implications for the treatment of ADHD.Conclusions: We conclude that further research of circadian function in ADHD should focus on detection of genetic markers (e.g., using human skin fibroblasts) and development of BL-based therapeutic interventions.

Media Use, Sleep Quality, and ADHD Symptoms in a Community Sample and a Sample of ADHD Patients Aged 8 to 18 Years

Objective: Relationships between sleep, screen-based media, and ADHD symptomatology were investigated using a case- and community-based approach. Method: N = 357 healthy and N = 61 children with ADHD (12.72 ± 2.83 years) completed a sleep and media questionnaire. To measure ADHD symptomatology, parents filled out the Strengths and Weaknesses of ADHD symptoms and Normal behavior (SWAN) scale. Two samples were formed: a matched (N = 61 patients and N = 61 controls) and a community sample (N = 357 healthy participants and N = 20 patients). Results: Compared with controls, participants with ADHD reported delayed sleep onset and more screen time on school days. Adolescent patients showed more behavior promoting delayed sleep phase. In the community sample, media time, sleep deviation, and circadian rhythm were correlated with ADHD symptomatology. Furthermore, media time, sleep-wake behavior, and sleep deviation were predictive of ADHD symptomatology (variance explained = 4%-15%). Conclusion: Longer media time and inadequate sleep-wake behavior increase the risk of ADHD-like symptoms. However, research using objective assessments is needed to disentangle this distinct association and to provide possible directions for intervention.

Sleep and Circadian Medicine

Fundamental aspects of neurobiology are time-of-day regulated. Therefore, it is not surprising that neurodegenerative and psychiatric diseases are accompanied by sleep and circadian rhythm disruption. Although the direction of causation remains unclear, abnormal sleep-wake patterns often occur early in disease, exacerbate progression, and are a common primary complaint from patients. Circadian medicine incorporates knowledge of 24-hour biological rhythms to improve treatment. This article highlights how research and technologic advances in circadian biology might translate to improved patient care.

The relationship between chronotype and obesity in children and adolescent with attention deficit hyperactivity disorder

Children and adolescents with Attention Deficit Hyperactivity Disorder (ADHD) have a high prevalence of obesity, but the relationship between these two problems is not clear. Chronotype preferences may be one of the possible mechanisms underlying the link between ADHD and obesity. This is the first study to investigate whether chronotype preferences are a mechanism linking ADHD symptoms to obesity in children and adolescents. This cross-sectional study included 110 drug-naive children and adolescents aged 7-17 years with ADHD. The Kiddie Schedule for Affective Disorders and Schizophrenia-Present and Lifetime Version (K-SADS-PL) was used to diagnose ADHD or to exclude psychiatric comorbidity. The Conners' Parents Rating Scale-Revised Short Version (CPRS-RS) and Children's Chronotype Questionnaire (CCQ) were used to assess the severity of ADHD symptoms and chronotype preferences. Body mass index (BMI) was calculated and classified according to national age- and gender-specific reference values. The participants were divided into three groups as normal weight (<85%, n = 38), overweight (85%-95%, n = 30) and obesity (>95%, n = 42) according to their BMI percentile. There were statistically significant differences between the three groups in terms of chronotype preference (p = .000). Morningness preference was 86.84% in the normal BMI group and 26.19% in the obese BMI group. Eveningness preference was 7.89% in the normal BMI group and 61.90% in the obese BMI group. There was a correlation between the BMI percentile scores and the morningness/eveningness scale (M/E) scores. Moreover, there was a correlation between the BMI percentile scores and the oppositional and ADHD index scores. According to logistic regression analysis, the odds ratio of having evening type for obesity was 5.66 and the odds ratio of having morning type for normal weight was 13.03. Independently from ADHD symptoms, eveningness was directly related to obesity and morningness was directly related to normal weight. Prospective studies should be performed to better understand the relationship between ADHD, overweight/obesity and chronotype.

Impact of adult attention deficit hyperactivity disorder and medication status on sleep/wake behavior and molecular circadian rhythms

Attention deficit hyperactivity disorder (ADHD) is a common neuropsychiatric condition that has been strongly associated with changes in sleep and circadian rhythms. Circadian rhythms are near 24-h cycles that are primarily generated by an endogenous circadian timekeeping system, encoded at the molecular level by a panel of clock genes. Stimulant and non-stimulant medication used in the management of ADHD has been shown to potentially impact on circadian processes and their behavioral outputs. In the current study, we have analyzed circadian rhythms in daily activity and sleep, and the circadian gene expression in a cohort of healthy controls (N = 22), ADHD participants not using ADHD-medication (N = 17), and participants with ADHD and current use of ADHD medication (N = 17). Rhythms of sleep/wake behavior were assessed via wrist-worn actigraphy, whilst rhythms of circadian gene expression were assessed ex-vivo in primary human-derived dermal fibroblast cultures. Behavioral data indicate that patients with ADHD using ADHD-medication have lower relative amplitudes of diurnal activity rhythms, lower sleep efficiency, more nocturnal activity but not more nocturnal wakenings than both controls and ADHD participants without medication. At the molecular level, there were alterations in the expression of PER2 and CRY1 between ADHD individuals with no medication compared to medicated ADHD patients or controls, whilst CLOCK expression was altered in patients with ADHD and current medication. Analysis of fibroblasts transfected with a BMAL1:luc reporter showed changes in the timing of the peak expression across the three groups. Taken together, these data support the contention that both ADHD and medication status impact on circadian processes.

CLOCK Polymorphisms in Attention-Deficit/Hyperactivity Disorder (ADHD): Further Evidence Linking Sleep and Circadian Disturbances and ADHD

Circadian and sleep disorders, short sleep duration, and evening chronotype are often present in attention-deficit/hyperactivity disorder (ADHD). CLOCK, considered the master gene in the circadian rhythm, has been explored by few studies. Understanding the relationship between ADHD and CLOCK may provide additional information to understand the correlation between ADHD and sleep problems. In this study, we aimed to explore the association between ADHD and CLOCK, using several genetic markers to comprehensively cover the gene extension. A total of 259 ADHD children and their parents from a Brazilian clinical sample were genotyped for eight single nucleotide polymorphisms (SNPs) in the CLOCK locus. We tested the individual markers and the haplotype effects using binary logistic regression. Binary logistic and linear regressions considering ADHD symptoms among ADHD cases were conducted as secondary analysis. As main result, the analysis showed a risk effect of the G-A-T-G-G-C-G-A (rs534654, rs1801260, rs6855837, rs34897046, rs11931061, rs3817444, rs4864548, rs726967) haplotype on ADHD. A suggestive association between ADHD and rs534654 was observed. The results suggest that the genetic susceptibility to circadian rhythm attributed to the CLOCK gene may play an important role on ADHD.

Genome-wide identification and expression analyses of WRKY transcription factor family members from chickpea (Cicer arietinum L.) reveal their role in abiotic stress-responses

BACKGROUND

WRKY proteins play a vital role in the regulation of several imperative plant metabolic processes and pathways, especially under biotic and abiotic stresses. Although WRKY genes have been characterized in various major crop plants, their identification and characterization in pulse legumes is still in its infancy. Chickpea (Cicer arietinum L.) is the most important pulse legume grown in arid and semi-arid tropics.

OBJECTIVE

In silico identification and characterization of WRKY transcription factor-encoding genes in chickpea genome.

METHODS

For this purpose, a systematic genome-wide analysis was carried out to identify the non-redundant WRKY transcription factors in the chickpea genome.

RESULTS

We have computationally identified 70 WRKY-encoding non-redundant genes which were randomly distributed on all the chickpea chromosomes except chromosome 8. The evolutionary phylogenetic analysis classified the WRKY proteins into three major groups (I, II and III) and seven sub-groups (IN, IC, IIa, IIb, IIc, IId and IIe). The gene structure analysis revealed the presence of 2-7 introns among the family members. Along with the presence of absolutely conserved signatory WRKY domain, 19 different domains were also found to be conserved in a group-specific manner. Insights of gene duplication analysis revealed the predominant role of segmental duplications for the expansion of WRKY genes in chickpea. Purifying selection seems to be operated during the evolution and expansion of paralogous WRKY genes. The transcriptome data-based in silico expression analysis revealed the differential expression of CarWRKY genes in root and shoot tissues under salt, drought, and cold stress conditions. Moreover, some of these genes showed identical expression pattern under these stresses, revealing the possibility of involvement of these genes in conserved abiotic stress-response pathways.

CONCLUSION

This genome-wide computational analysis will serve as a base to accelerate the functional characterization of WRKY TFs especially under biotic and abiotic stresses.

[Diagnosis and comorbidities of Circadian Rhythm Sleep Disorders]

Circadian rhythm sleep disorders (CRSD) result from a disturbed endogenous clock (intrinsic CRSD) or from a misalignment between the biological clock and an imposed environment (extrinsic CRSD). Among intrinsic CRSD, one distinguishes the delayed sleep-wake phase disorder, the advanced sleep-wake phase disorder, the irregular sleep-wake rhythm disorder and the non-24-hour sleep-wake rhythm disorder. Shift work disorder, jet lag disorder and circadian sleep-wake disorder not otherwise specified are extrinsic CRSD. Prevalences of the different CRSD remain largely unknown. Some CRSD are particularly frequent such as sleep delayed phase syndrome in adolescents. Overall, CRSD are probably under-diagnosed. CRSD generate insomnia and excessive daytime somnolence. A biological clock dysfunction has to be evoked in case of insomnia or sleepiness. Furthermore, as CRSD can overlap with other sleep disorders, their diagnosis and treatment are essential. CRSD cause significant mental, physical or socio-professional sufferings. They are frequently associated with comorbidities, mainly neurodevelopmental, psychiatric and neurodegenerative disorders. Regarding neurodevelopmental comorbidities, therapy using a chronobiological approach is complementary to the usual clinical care. It helps to limit the significant impact of CRSD on quality of live, daytime functioning, social interactions and neurocognitive difficulties in the children. In psychiatry, sleep disorders and circadian rhythms sleep-wake disorders are a factor of vulnerability, of suicidal risk, of relapse and pharmacoresistance. Thus, diagnosis of CRSD associated with a psychiatric disorder is of major importance. Treatment using a chronobiological approach reinforcing the entrainment of the sleep-wake cycle is complementary to usual treatments. Sleep disorders and circadian sleep-wake rhythm disorders can be a preclinical sign of Alzheimer's and Parkinson's disease. In the elderly, a beginning neurodegenerative disorder can be associated with a CRSD and complaints of sleepiness, nocturnal awakenings and/or irregular sleep-wake cycles. Patients affected by neurogenerative disorders are particularly vulnerable for having CRSD. Data from different studies suggest that CRSD participate in pathophysiology of Alzheimer's disease. Even though treatment of CRSD associated with neurodegenerative disorders is entirely part of the treatment strategy, it remains uncertain to which extend this treatment may impact disease progression.

Review: Schlafprobleme und psychische Störungen im Kindes- und Jugendalter

Zusammenfassung. Schlafprobleme und -störungen sind in Kindheit und Jugendalter weitverbreitet. Dieser Review beleuchtet den Zusammenhang zwischen Schlafproblemen und psychischen Störungen im Kindes- und Jugendalter. Schlafprobleme und -störungen gelten zum einen als Risikofaktoren für die Entwicklung psychischer Störungen, aber auch als Symptom und Auswirkung psychischer Störungen. Oft stehen Schlafverhalten und Psychopathologie in einer Wechselwirkung, sodass Schlafprobleme zur Intensität und Aufrechterhaltung psychischer Störungen beitragen. Dieser bidirektionale Zusammenhang ist sowohl in der frühen Kindheit als auch im Schulalter und bei Jugendlichen zu beobachten. Viele Studien konnten zeigen, dass es einen langfristigen Zusammenhang über die kindliche Entwicklung hinweg gibt. Sowohl Umweltfaktoren als auch genetische Faktoren scheinen bei der Entwicklung und Aufrechterhaltung dieses Zusammenhangs eine Rolle zu spielen. Diverse Forschungsergebnisse zeigen, dass die Behandlung von psychischen Störungen und die Behandlung von Schlafproblemen sich wechselseitig positiv beeinflussen. Daher ist die Berücksichtigung von Schlafproblemen in der Diagnostik und Behandlung, aber auch in der Prävention von psychischen Störungen dringend anzuraten.

Understanding Neurodevelopmental Disorders: The Promise of Regulatory Variation in the 3'UTRome

Neurodevelopmental disorders have a strong genetic component, but despite widespread efforts, the specific genetic factors underlying these disorders remain undefined for a large proportion of affected individuals. Given the accessibility of exome sequencing, this problem has thus far been addressed from a protein-centric standpoint; however, protein-coding regions only make up ∼1% to 2% of the human genome. With the advent of whole genome sequencing we are in the midst of a paradigm shift as it is now possible to interrogate the entire sequence of the human genome (coding and noncoding) to fill in the missing heritability of complex disorders. These new technologies bring new challenges, as the number of noncoding variants identified per individual can be overwhelming, making it prudent to focus on noncoding regions of known function, for which the effects of variation can be predicted and directly tested to assess pathogenicity. The 3'UTRome is a region of the noncoding genome that perfectly fulfills these criteria and is of high interest when searching for pathogenic variation related to complex neurodevelopmental disorders. Herein, we review the regulatory roles of the 3'UTRome as binding sites for microRNAs or RNA binding proteins, or during alternative polyadenylation. We detail existing evidence that these regions contribute to neurodevelopmental disorders and outline strategies for identification and validation of novel putatively pathogenic variation in these regions. This evidence suggests that studying the 3'UTRome will lead to the identification of new risk factors, new candidate disease genes, and a better understanding of the molecular mechanisms contributing to neurodevelopmental disorders.

The role of CLOCK gene in psychiatric disorders: Evidence from human and animal research

The circadian clock system drives daily rhythms in physiology, metabolism, and behavior in mammals. Molecular mechanisms of this system consist of multiple clock genes, with Circadian Locomotor Output Cycles Kaput (CLOCK) as a core member that plays an important role in a wide range of behaviors. Alterations in the CLOCK gene are associated with common psychiatric disorders as well as with circadian disturbances comorbidities. This review addresses animal, molecular, and genetic studies evaluating the role of the CLOCK gene on many psychiatric conditions, namely autism spectrum disorder, schizophrenia, attention-deficit/hyperactivity disorder, major depressive disorder, bipolar disorder, anxiety disorder, and substance use disorder. Many animal experiments focusing on the effects of the Clock gene in behavior related to psychiatric conditions have shown consistent biological plausibility and promising findings. In humans, genetic and gene expression studies regarding disorder susceptibility, sleep disturbances related comorbidities, and response to pharmacological treatment, in general, are in agreement with animal studies. However, the number of controversial results is high. Literature suggests that the CLOCK gene exerts important influence on these conditions, and influences the susceptibility to phenotypes of psychiatric disorders.

Common and specific genes and peripheral biomarkers in children and adults with attention-deficit/hyperactivity disorder

OBJECTIVES

Elucidating the biological mechanisms involved in attention-deficit/hyperactivity disorder (ADHD) has been challenging. Relatively unexplored is the fact that these mechanisms can differ with age.

METHODS

We present an overview on the major differences between children and adults with ADHD, describing several studies from genomics to metabolomics performed in ADHD children and in adults (cADHD and aADHD, respectively). A systematic search (up until February 2016) was conducted.

RESULTS

From a PRISMA flow-chart, a total of 350 and 91 genomics and metabolomics studies were found to be elligible for cADHD and aADHD, respectively. For children, associations were found for genes belonging to dopaminergic (SLC6A3, DRD4 and MAOA) and neurodevelopmental (LPHN3 and DIRAS2) systems and OPRM1 (Yates corrected P = 0.016; OR = 2.27 95%CI: 1.15-4.47). Studies of adults have implicated circadian rhythms genes, HTR2A, MAOB and a more generic neurodevelopmental/neurite outgrowth network (BCHE, SNAP25, BAIAP2, NOS1/NO, KCNIP4 and SPOCK3; Yates corrected P = 0.007; OR = 3.30 95%CI: 1.33-8.29). In common among cADHD and aADHD, the most significant findings are for oxidative stress proteins (MAD, SOD, PON1, ARES, TOS, TAS and OSI), and, in the second level, DISC1, DBH, DDC, microRNA and adiponectin.

CONCLUSIONS

Through a convergent functional genomics, this review contributes to clarification of which genetic/biological mechanisms differ with age. The effects of some genes do not change throughout the lifetime, whereas others are linked to age-specific stages. Additional research and further studies are needed to generate firmer conclusions that might someday be useful for predicting the remission and persistence of the disorder. Despite the limitations, some of these genes/proteins could be potential useful biomarkers to discriminate cADHD from aADHD.

Sleep, chronotype, and sleep hygiene in children with attention-deficit/hyperactivity disorder, autism spectrum disorder, and controls

Sleep problems are highly prevalent in ADHD and autism spectrum disorder (ASD). Better insight in the etiology is of clinical importance since intervention and prevention strategies of sleep problems are directed at underlying mechanisms. We evaluated the association of sleep problems and sleep patterns with sleep hygiene (behavioral/environmental practices that influence sleep quality, e.g. caffeine use), access to electronic media, chronotype, and anxiety/depression in children aged 6-12 years with ADHD, ASD, or typical development (TD) using parental questionnaires. ANOVA and linear regression analyses were adjusted for age and sex. Children with ADHD and ASD showed more sleep problems (63.6 and 64.7%, vs 25.1% in TD) and shorter sleep duration than controls, while differences between ADHD and ASD were not significant. Sleep hygiene was worse in ADHD and ASD compared to TD, however, the association of worse sleep hygiene with more sleep problems was only significant in ASD and TD. There was a significant association of access to electronic media with sleep problems only in typically developing controls. Chronotype did not differ significantly between groups, but evening types were associated with sleep problems in ADHD and TD. Associations of greater anxiety/depression with more sleep problems were shown in ADHD and TD; however, anxiety/depression did not moderate the effects of chronotype and sleep hygiene. We conclude that sleep problems are highly prevalent in ADHD and ASD, but are differentially related to chronotype and sleep hygiene. In ASD, sleep problems are related to inadequate sleep hygiene and in ADHD to evening chronotype, while in TD both factors are important. Clinical implications are discussed.

Suicide attempts in children and adolescents: The place of clock genes and early rhythm dysfunction

Suicide remains one of the leading causes of death among young people, and suicidal ideation and behavior are relatively common in healthy and clinical populations. Suicide risk in childhood and adolescence is often approached from the perspective of nosographic categories to which predictive variables for suicidal acts are often linked. The cascading effects resulting from altered clock genes in a pediatric population could participate in biological rhythm abnormalities and the emergence of suicide attempts through impaired regulation of circadian rhythms and emotional states with neurodevelopmental effects. Also, early trauma and stressful life events can alter the expression of clock genes and contribute to the emergence of suicide attempts. Alteration of clock genes might lead to desynchronized and abnormal circadian rhythms impairing in turn the synchronization between external and internal rhythms and therefore the adaptation of the individual to his/her internal and external environment with the development of psychiatric disorders associated with increased risk for suicide attempts.

Correcting delayed circadian phase with bright light therapy predicts improvement in ADHD symptoms: A pilot study

Attention-deficit/hyperactivity disorder (ADHD) is a common condition with comorbid insomnia reported in >70% of children and adults. These patients demonstrate delays in sleep-wake rhythms, nocturnal rise in melatonin, and early morning rise in cortisol. Given that standard psychopharmacologic treatments for ADHD often do not completely control symptoms in participants with circadian rhythm delay, we sought to test whether bright light therapy (BLT) advances circadian rhythms and further reduces ADHD symptoms over standard treatments. In addition to standard of care, participants with ADHD diagnosis underwent 1 week of baseline assessment followed by 2-weeks of 30-min morning 10,000-lux BLT beginning 3 h after mid-sleep time. Participants minimized overhead light after 4 p.m., wore an actigraphy watch, and recorded BLT time on daily sleep logs. Dim Light Melatonin Onset (DLMO) was assessed at baseline and after 2-week treatment. ADHD symptoms were measured by the ADHD-Rating Scales (ADHD-RS). BLT significantly advanced the phase of DLMO by 31 min [mean time (SEM), 20:36 (0:21) advanced to 20:05 (0:20)] and mid-sleep time by 57 min [4:37 (0:22) advanced to 3:40 (0:16); paired t-tests, p = 0.002 and 0.004, respectively). Phase advances (in DLMO or mid-sleep time) were significantly correlated with decreased ADHD-RS total scores (p = 0.027 and 0.044) and Hyperactive-Impulsive sub-scores (p = 0.014 and 0.013, respectively). Actigraphy analysis for a subset of 8 participants with significant DLMO phase advance revealed no significant changes in total sleep time, sleep efficiency, wake after sleep onset, or percent wake during sleep interval. This is the first successful use of BLT for advancing melatonin phase and improving ADHD symptoms in adults. BLT may be a complementary treatment for both delayed sleep timing and ADHD symptoms in adults.

Clock Genes and Altered Sleep-Wake Rhythms: Their Role in the Development of Psychiatric Disorders

In mammals, the circadian clocks network (central and peripheral oscillators) controls circadian rhythms and orchestrates the expression of a range of downstream genes, allowing the organism to anticipate and adapt to environmental changes. Beyond their role in circadian rhythms, several studies have highlighted that circadian clock genes may have a more widespread physiological effect on cognition, mood, and reward-related behaviors. Furthermore, single nucleotide polymorphisms in core circadian clock genes have been associated with psychiatric disorders (such as autism spectrum disorder, schizophrenia, anxiety disorders, major depressive disorder, bipolar disorder, and attention deficit hyperactivity disorder). However, the underlying mechanisms of these associations remain to be ascertained and the cause–effect relationships are not clearly established. The objective of this article is to clarify the role of clock genes and altered sleep–wake rhythms in the development of psychiatric disorders (sleep problems are often observed at early onset of psychiatric disorders). First, the molecular mechanisms of circadian rhythms are described. Then, the relationships between disrupted circadian rhythms, including sleep–wake rhythms, and psychiatric disorders are discussed. Further research may open interesting perspectives with promising avenues for early detection and therapeutic intervention in psychiatric disorders.

Circadian gene variants and breast cancer

The endogenous and self-sustained circadian rhythm generated and maintained in suprachiasmatic nucleus and peripheral tissues can coordinate various molecular, biochemical and physiological processes in living organisms resulting in the adaptation to environmental cues, e.g. light. Multifactorial breast cancer etiology also involves circadian gene alterations, especially among individuals exposed to light at night. Indeed, shift work that causes circadian disruption has been classified by the International Agency for Research on Cancer as a probable human carcinogen, group 2A. Thus it seems extremely important to recognize specific susceptible gene variants among around 20 candidate circadian genes that may be linked with breast cancer etiology. The aim of this review was to evaluate recent data investigating a putative link between circadian gene polymorphisms and breast cancer risk. We summarize fifteen epidemiological studies, including five studies on shift work that have indicated BMAL1, BMAL2, CLOCK, NPAS2, CRY1, CRY2, PER1, PER3 and TIMELESS as a candidate breast cancer risk variants.

Association between the CLOCK gene 3111 T > C polymorphism and an irregular menstrual cycle in Korean adolescents

The menstrual cycle is an example of a human infradian rhythm, but an altered sleep-wake cycle or a disrupted circadian rhythm can change the regularity of the menstrual cycle. In this study, we investigated whether an irregular menstrual cycle is associated with polymorphisms in the CLOCK (3111T > C) and/or PER3 (variable number tandem repeat, VNTR) genes, which are known to have an impact on the circadian rhythm. One hundred ninety-seven postmenarchal, adolescent girls from two girls' high schools in Seoul, Korea, were studied. All participants were requested to complete the Perceived Stress Scale (PSS), the State-Trait Anxiety Inventory (STAI), and the Beck Depression Inventory (BDI) to assess the emotional distress that might cause menstrual irregularity. Every participant donated a blood sample from which DNA was extracted and genotyped for the CLOCK 3111T > C and PER3 VNTR polymorphisms. A significant association was found between the CLOCK 3111T > C genotype and irregular menstrual cycles. Subjects with the 3111T > C genotype had a high risk of an irregular menstrual cycle compared with 3111T/T homozygous subjects (odds ratio [OR] = 2.88; 95% confidence interval [CI]: 1.26-6.55). When multivariate logistic regression analysis was performed to adjust for age, PSS, STAI, BDI and BMI, subjects with the 3111T > C polymorphism showed a significantly increased OR for irregular menstrual cycles (OR = 3.09; 95% CI: 1.32-7.21). There was no significant association between the PER3 VNTR polymorphism and the irregularity of the menstrual cycle (p > 0.05). The results of this study suggest that the CLOCK 3111T > C polymorphism could be an independent risk factor for irregular menstrual cycles, irrespective of psychological distress and endocrine or metabolic conditions, and could be used as a molecular marker for gynecological studies on this aspect.

Circadian rhythms and attention deficit hyperactivity disorder: The what, the when and the why

Attention deficit hyperactivity disorder (ADHD) is a common neurodevelopmental condition characterised by impulsivity, inattention and hyperactivity. Aside from these core psychopathologies, sleep disturbances are found to be highly comorbid with ADHD, and indeed dysregulated sleep may contribute to some of the symptoms of the disorder. It is not clear how sleep disturbances come to be so common in ADHD, but one putative mechanism is through the circadian timekeeping system. This system underpins the generation of near 24-hour rhythms in a host of physiological, behavioural and psychological parameters, and is a key determinant of the sleep/wake cycle. In this paper we review the evidence for sleep and circadian rhythm disturbance in ADHD, examine the possible mechanistic links between these factors and the disorder and discuss future directions through which the circadian clock can be targetted for ADHD symptom relief.

Treatment outcomes after methylphenidate in adults with attention-deficit/hyperactivity disorder treated with lisdexamfetamine dimesylate or atomoxetine

PURPOSE

To compare treatment adherence, discontinuation, add-on, and daily average consumption (DACON) among adults with attention-deficit/hyperactivity disorder receiving second-line lisdexamfetamine dimesylate (LDX) or atomoxetine (ATX), following methylphenidate.

PATIENTS AND METHODS

A retrospective cohort study using US commercial claims databases (Q2/2009-Q3/2013).

RESULTS

At month 12, the LDX cohort (N=2,718) had a higher adherence level (proportion of days covered: 0.48 versus 0.30, P<0.001) and was less likely to discontinue (Kaplan-Meier estimate: 63% versus 85%, P<0.001) than the ATX cohort (N=674). There were no statistical differences in treatment add-on rates between cohorts (Kaplan-Meier estimate: 26% versus 25%, P=0.297). The LDX cohort had a lower DACON (1.10 versus 1.31, P<0.001) and was less likely to have a DACON >1 (adjusted odds ratio: 0.20, 95% confidence interval: 0.15-0.25, P<0.001) than the ATX cohort.

CONCLUSION

Adults with attention-deficit/hyperactivity disorder treated with LDX following methylphenidate had a higher treatment adherence and lower discontinuation and DACON relative to those treated with ATX following methylphenidate.

The ticking clock of Cayo Santiago macaques and its implications for understanding human circadian rhythm disorders

The circadian clock disorders in humans remain poorly understood. However, their impact on the development and progression of major human conditions, from cancer to insomnia, metabolic or mental illness becomes increasingly apparent. Addressing human circadian disorders in animal models is, in part, complicated by inverse temporal relationship between the core clock and specific physiological or behavioral processes in diurnal and nocturnal animals. Major advantages of a macaque model for translational circadian research, as a diurnal vertebrate phylogenetically close to humans, are further emphasized by the discovery of the first familial circadian disorder in non‐human primates among the rhesus monkeys originating from Cayo Santiago. The remarkable similarity of their pathological phenotypes to human Delayed Sleep Phase Disorder (DSPD), high penetrance of the disorder within one branch of the colony and the large number of animals available provide outstanding opportunities for studying the mechanisms of circadian disorders, their impact on other pathological conditions, and for the development of novel and effective treatment strategies. Am. J. Primatol. 78:117–126, 2016. © 2016 The Authors. American Journal of Primatology published by Wiley Periodicals, Inc.

Circadian modulation of dopamine levels and dopaminergic neuron development contributes to attention deficiency and hyperactive behavior

Attention-deficit/hyperactivity disorder (ADHD) is one of the most prevalent psychiatric disorders in children and adults. While ADHD patients often display circadian abnormalities, the underlying mechanisms are unclear. Here we found that the zebrafish mutant for the circadian gene period1b (per1b) displays hyperactive, impulsive-like, and attention deficit-like behaviors and low levels of dopamine, reminiscent of human ADHD patients. We found that the circadian clock directly regulates dopamine-related genes monoamine oxidase and dopamine β hydroxylase, and acts via genes important for the development or maintenance of dopaminergic neurons to regulate their number and organization in the ventral diencephalic posterior tuberculum. We then found that Per1 knock-out mice also display ADHD-like symptoms and reduced levels of dopamine, thereby showing highly conserved roles of the circadian clock in ADHD. Our studies demonstrate that disruption of a circadian clock gene elicits ADHD-like syndrome. The circadian model for attention deficiency and hyperactive behavior sheds light on ADHD pathogenesis and opens avenues for exploring novel targets for diagnosis and therapy for this common psychiatric disorder.

Circadian clock and stress interactions in the molecular biology of psychiatric disorders

Many psychiatric disorders are characterized by circadian rhythm abnormalities, including disturbed sleep/wake cycles, changes in locomotor activity, and abnormal endocrine function. Animal models with mutations in circadian "clock genes" commonly show disturbances in reward processing, locomotor activity and novelty seeking behaviors, further supporting the idea of a connection between the circadian clock and psychiatric disorders. However, if circadian clock dysfunction is a common risk factor for multiple psychiatric disorders, it is unknown if and how these putative clock abnormalities could be expressed differently, and contribute to multiple, distinct phenotypes. One possible explanation is that the circadian clock modulates the biological responses to stressful environmental factors that vary with an individual's experience. It is known that the circadian clock and the stress response systems are closely related: Circadian clock genes regulate the physiological sensitivity to and rhythmic release of glucocorticoids (GC). In turn, GCs have reciprocal effects on the clock. Since stressful life events or increased vulnerability to stress are risk factors for multiple psychiatric disorders, including post-traumatic stress disorder (PTSD), attention deficit hyperactivity disorder (ADHD), bipolar disorder (BD), major depressive disorder (MDD), alcohol use disorder (AUD) and schizophrenia (SCZ), we propose that modulation of the stress response is a common mechanism by which circadian clock genes affect these illnesses. Presently, we review how molecular components of the circadian clock may contribute to these six psychiatric disorders, and present the hypothesis that modulation of the stress response may constitute a common mechanism by which the circadian clock affects multiple psychiatric disorders.

Adenosinergic regulation of striatal clock gene expression and ethanol intake during constant light

Circadian rhythm and sleep disruptions occur frequently in individuals with alcohol use disorders (AUD) and present significant barriers to treatment. Recently, a variant of adenosine transporter, equilibrative nucleoside transporter 1 (ENT1), was associated with the co-occurrence of sleep problems and AUD. We have previously shown that mice lacking ENT1 (ENT1 KO) have reduced adenosine levels in the striatum and drink more alcohol compared with wild types (WT). However, it is unknown whether ENT1 deletion disrupts circadian rhythms, which may contribute to alcohol preference in ENT1 KO mice. Here we used these mice to determine whether endogenous adenosine regulates circadian genetic and behavioral rhythms and influences alcohol intake during chronodisruption. We examined circadian locomotor activity in ENT1 KO vs WT littermates and found that ENT1 KO mice were both active earlier and hyperactive compared with WT mice at night. We used real-time PCR and immunohistochemistry to estimate striatal clock gene levels and found that PER2 expression in the striatum was blunted by ENT1 deletion or A2A receptor (A2AR) antagonism. Next, we exposed ENT1 KO and WT mice to constant light (LL) and found further elevation in ethanol intake in ENT1 KO, but not in WT mice, supporting the notion that circadian dysfunction may contribute to increased alcohol intake in ENT1 KO mice. Finally, we showed that A2AR agonist administration normalized PER1 and PER2 expression and circadian locomotor activity in ENT1 KO mice. Together, our results demonstrate that adenosine signaling regulates cellular and behavioral circadian timing and influences alcohol intake during chronodisruption.

Advances in molecular genetic studies of attention deficit hyperactivity disorder in China

SUMMARY

Attention deficit hyperactivity disorder (ADHD) is a common psychiatric condition in children worldwide that typically includes a combination of symptoms of inattention and hyperactivity/impulsivity. Genetic factors are believed to be important in the development and course of ADHD so many candidate genes studies and genome-wide association studies (GWAS) have been conducted in search of the genetic mechanisms that cause or influence the condition. This review provides an overview of gene association and pharmacogenetic studies of ADHD from mainland China and elsewhere that use Han Chinese samples. To date, studies from China and elsewhere remain inconclusive so future studies need to consider alternative analytic techniques and test new biological hypotheses about the relationship of neurotransmission and neurodevelopment to the onset and course of this disabling condition.

The circadian rhythm in adult attention-deficit/hyperactivity disorder: current state of affairs

Adults with ADHD often have sleep problems that are caused by a delay of their internal circadian rhythm system. Such individuals are often typified as 'evening' or 'night' persons. This review focuses on the link between ADHD symptoms and the evening typology through multiple pathways. Etiology of the internal circadian rhythm system, the genetic basis for evening typology, overlap between ADHD symptoms and evening preference and risk factors for various chronic health conditions, including metabolic syndrome and cancer, are discussed. The treatment perspectives to reset the delayed rhythm in adults with ADHD involve psychoeducation on sleep hygiene, melatonin in the afternoon or evening and bright light therapy in the morning.

Prevalence and correlates of attention deficit hyperactivity disorder in adults from a French community sample

Validated tools are lacking in languages such as French to diagnose attention deficit hyperactivity disorder (ADHD) in adults. The Adult ADHD Symptoms Self-Report (ASRS) was filled out by 1171 parents of 900 school-aged youths in the context of the Children and Parents With ADHD and Related Disorders study. Prevalence estimates based on three scoring methods are compared (6-item screener, all 18 items, or the screener followed by the 12 remaining items). On the basis of the recommended and more conservative scoring method, the overall prevalence of ADHD symptoms is estimated to be 2.99%, without significant group differences between sexes or between younger and older adults. Potential correlates of ADHD symptoms were also examined in their relatives (children, brothers/sisters, uncles/aunts, and parents) as follows: birth order, level of education, body mass index categories, enuresis, suicide attempts, depression, and learning disabilities. Adults can be screened for ADHD symptoms using the ASRS; negative long-term outcomes should be assessed in patients' relatives too.