Human CLOCK gene-associated attention deficit hyperactivity disorder-related features in healthy adults: quantitative association study using Wender Utah Rating Scale

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.

Cry1Δ11 mutation induces ADHD-like symptoms through hyperactive dopamine D1 receptor signaling

Attention-deficit hyperactivity disorder (ADHD) is a highly heritable neurodevelopmental disorder that affects approximately 5.3% of children and approximately 2.5% of adults. There is an intimate relationship between ADHD and sleep disturbance. Specifically, individuals carry a mutation in the core circadian gene CRY1 (c. 1657 + 3A > C), which results in the deletion of exon 11 expression in the CRY1 protein (CRY1Δ11), causing them to exhibit typical ADHD symptoms. However, the underlying mechanism is still elusive. In this study, we demonstrate that Cry1Δ11 (c. 1717 + 3A > C) mice showed ADHD-like symptoms, including hyperactivity, impulsivity, and deficits in learning and memory. A hyperactive cAMP signaling pathway was found in the nucleus accumbens (NAc) of Cry1Δ11 mice. We further demonstrated that upregulated c-Fos was mainly localized in dopamine D1 receptor-expressing medium spiny neurons (DRD1-MSNs) in the NAc. Neuronal excitability of DRD1-MSNs in the NAc of Cry1Δ11 mice was significantly higher than that of WT controls. Mechanistically, the CRY1Δ11 protein, in contrast to the WT CRY1 protein, failed to interact with the Gαs protein and inhibit DRD1 signaling. Finally, the DRD1 antagonist SCH23390 normalized most ADHD-like symptoms in Cry1Δ11 mice. Thus, our results reveal hyperactive DRD1 signaling as an underlying mechanism and therapeutic target for ADHD induced by the highly prevalent CRY1Δ11 mutation.

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.

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.

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.

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.

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.

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.

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.

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.

Association between the 5-HTTLPR Genotype and Childhood Characteristics in Mood Disorders

Objective

The features of childhood attention deficit hyperactivity disorder (ADHD) are significantly associated with adult mood disorders. Some genetic factors may be common to both ADHD and mood disorders underlie the association between these two phenotypes. The present study aimed to determine whether a genetic role may be played by the serotonin transporter-linked polymorphic region (5-HTTLPR) in the childhood ADHD features of adult patients with mood disorders.

Methods

The present study included 232 patients with major depressive disorder (MDD), 154 patients with bipolar disorder (BPD), and 1,288 normal controls. Childhood ADHD features were assessed with the Korean version of the Wender Utah Rating Scale (WURS-K). The total score and the scores of three factors (impulsivity, inattention, and mood instability) from the WURS-K were analyzed to determine whether they were associated with the 5-HTTLPR genotype.

Results

In the BPD type II group, the 5-HTTLPR genotype was significantly associated with the total score (p=0.029) and the impulsivity factor (p=0.004) on the WURS-K. However, the inattention and mood instability factors were not associated with the 5-HTTLPR genotype. BPD type I, MDD and normal control groups did not exhibit any significant associations between the WURS-K scores and the 5-HTTLPR genotype.

Conclusion

The findings suggest that the 5-HTTLPR genotype may play a role in the impulsivity component of childhood ADHD in patients with BPD type II. Because of a small sample size and a single candidate gene, further studies investigating other candidate genes using a larger sample are warranted to determine any common genetic links.

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.

PER2 rs2304672, CLOCK rs1801260, and PER3 rs57875989 polymorphisms are not associated with juvenile myoclonic epilepsy

Sleep disturbance is common in several epilepsy types, such as juvenile myoclonic epilepsy (JME). Genetic background could increase susceptibility to seizure and sleep abnormalities. From this perspective, a susceptibility gene for sleep disturbance or chronotype could contribute to the genetic susceptibility threshold for epilepsy and vice versa. Accordingly, we investigated whether functional clock gene polymorphisms (PER2 111C>G, CLOCK 3111T>C, and PER3 VNTR) might influence the risk for JME. All these polymorphisms have recently been reported to be associated with sleep disturbance, diurnal variation, and neurological diseases. The polymorphisms were genotyped in 97 patients and 212 controls using polymerase chain reaction or restriction fragment length polymorphism methods. No significant differences were observed in the genotypic and allelic frequencies of these polymorphisms between cases and controls even when analyses were restricted to patients that presented a diurnal preferential seizure occurrence. We also tested for interactions between polymorphisms by multifactor dimensionality reduction analysis. None of the combined genotypes differed significantly between the groups. These results present no evidence for an association of these polymorphisms with JME. Further studies including other types of epilepsy and/or other functional polymorphisms are required to investigate the possible relationship between clock genes and the genetic susceptibility to chronic seizure.