Evidence for genetic influences on sleep disturbance and sleep pattern in twins

Sleep regulation and host genetics

Due to the multifactorial and complex nature of rest, we focus on phenotypes related to sleep. Sleep regulation is a multifactorial process. In this chapter, we focus on those phenotypes inherent to sleep that are highly prevalent in the population, and that can be modulated by lifestyle, such as sleep quality and duration, insomnia, restless leg syndrome and daytime sleepiness. We, therefore, leave in the background those phenotypes that constitute infrequent pathologies or for which the current level of scientific evidence does not favour the implementation of practical approaches of this type. Similarly, the regulation of sleep quality is intimately linked to the regulation of the circadian rhythm. Although this relationship is discussed in the sections that require it, the in-depth study of circadian rhythm regulation at the molecular level deserves a separate chapter, and this is how it is dealt with in this volume.

Mediterranean diet adherence and sleep pattern: a systematic review of observational studies

BACKGROUND AND AIMS

Despite a huge body of evidence on the linkage between dietary intakes and pattern of sleeping, the findings are controversial. The current study aimed to summarize earlier findings on the association between adherence to Mediterranean diet (MD) and pattern of sleeping.

METHODS

This study performed based on PRISMA guideline. Systematically search was applied in PubMed, Scopus and Google Scholar to find out relevant publications appeared up to February 2023. No restrictions on language and time of publication were applied. Duplicate citations were removed. We included observational studies which assessed MD as the main exposure and kind of sleep disorders as the main outcome.

RESULTS

A total of 20 observational studies included. Out of these studies, two were cohort studies and 18 had a cross-sectional design. A total of 21,714 participants included. Usual dietary intakes were assessed using a validated Food Frequency Questionnaire, and a diet history questionnaire. Some studies did not report methods of measuring habitual dietary intakes. Adherence to MD was evaluated by KIDMED questionnaire, PREMED, alternate Mediterranean (aMed) questionnaire, MEDAS questionnaire, MedDietScore, MEDI-LITE score, modified Mediterranean Diet Score (mMDS), Mediterranean food pattern (MFP) and modified Mediterranean diet score (mMED). Pattern of sleeping was examined as sleep quality, sleep duration, sleep latency, sleep efficacy, sleepiness, sleep disturbance, taking a nap and some other sleep disorders.

CONCLUSION

In conclusion, findings of published studies highlighted the importance of consumption of MD for better sleep quality.

Shared genetic architecture and causal relationship between sleep behaviors and lifespan

Poor sleep health is associated with a wide array of increased risk for cardiovascular, metabolic and mental health problems as well as all-cause mortality in observational studies, suggesting potential links between sleep health and lifespan. However, it has yet to be determined whether sleep health is genetically or/and causally associated with lifespan. In this study, we firstly studied the genome-wide genetic association between four sleep behaviors (short sleep duration, long sleep duration, insomnia, and sleep chronotype) and lifespan using GWAS summary statistics, and both sleep duration time and insomnia were negatively correlated with lifespan. Then, two-sample Mendelian randomization (MR) and multivariable MR analyses were applied to explore the causal effects between sleep behaviors and lifespan. We found that genetically predicted short sleep duration was causally and negatively associated with lifespan in univariable and multivariable MR analyses, and this effect was partially mediated by coronary artery disease (CAD), type 2 diabetes (T2D) and depression. In contrast, we found that insomnia had no causal effects on lifespan. Our results further confirmed the negative effects of short sleep duration on lifespan and suggested that extension of sleep may benefit the physical health of individuals with sleep loss. Further attention should be given to such public health issues.

Multivariate genome-wide association study of sleep health demonstrates unity and diversity

There has been a recent push to focus sleep research less on disordered sleep and more on the dimensional sleep health. Sleep health incorporates several dimensions of sleep: chronotype, efficiency, daytime alertness, duration, regularity, and satisfaction with sleep. A previous study demonstrated sleep health domains correlate only moderately with each other at the genomic level (|rGs| = 0.11-0.51) and show unique relationships with psychiatric domains (controlling for shared variances, duration, alertness, and non-insomnia independently related to a factor for internalizing psychopathology). Of the domains assessed, circadian preference was the least genetically correlated with all other facets of sleep health. This pattern is important because it suggests sleep health should be considered a multifaceted construct rather than a unitary construct. Prior genome-wide association studies (GWASs) have vastly increased our knowledge of the biological underpinnings of specific sleep traits but have only focused on univariate analyses. We present the first multivariate GWAS of sleep and circadian health (multivariate circadian preference, efficiency, and alertness factors, and three single-indicator factors of insomnia, duration, and regularity) using genomic structural equation modeling. We replicated loci found in prior sleep GWASs, but also discovered "novel" loci for each factor and found little evidence for genomic heterogeneity. While we saw overlapping genomic enrichment in subcortical brain regions and shared associations with external traits, much of the genetic architecture (loci, mapped genes, and enriched pathways) was diverse among sleep domains. These results confirm sleep health as a family of correlated but genetically distinct domains, which has important health implications.

Potential genetic and epigenetic mechanisms in insomnia: A systematic review

Insomnia is a stress-related sleep disorder conceptualised within a diathesis-stress framework, which it is thought to result from predisposing factors interacting with precipitating stressful events that trigger the development of insomnia. Among predisposing factors genetics and epigenetics may play a role. A systematic review of the current evidence for the genetic and epigenetic basis of insomnia was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) system. A total of 24 studies were collected for twins and family heritability, 55 for genome-wide association studies, 26 about candidate genes for insomnia, and eight for epigenetics. Data showed that insomnia is a complex polygenic stress-related disorder, and it is likely to be caused by a synergy of genetic and environmental factors, with stress-related sleep reactivity being the important trait. Even if few studies have been conducted to date on insomnia, epigenetics may be the framework to understand long-lasting consequences of the interaction between genetic and environmental factors and effects of stress on the brain in insomnia. Interestingly, polygenic risk for insomnia has been causally linked to different mental and medical disorders. Probably, by treating insomnia it would be possible to intervene on the effect of stress on the brain and prevent some medical and mental conditions.

Insomnia as a Risk Factor for Substance Use Disorders in Women

Gender differences exist for both insomnia and substance use disorders. Women show a higher prevalence of insomnia and increased susceptibility to the effects of drugs than men. Importantly, a growing body of evidence suggests that insufficient sleep predicts and puts individuals at a higher risk for substance use and associated psychosocial problems. However, the role of insomnia in substance use disorders among women remains poorly understood. The present article discusses gender differences in insomnia and in substance use disorders and reviews evidence suggesting that an increased prevalence of insomnia may be a risk factor for substance use disorders in women.

Polygenic predisposition, sleep duration, and depression: evidence from a prospective population-based cohort

Suboptimal sleep durations and depression frequently cooccur. Short-sleep and long-sleep are commonly thought of as symptoms of depression, but a growing literature suggests that they may be prodromal. While each represents a process of mutual influence, the directionality between them remains unclear. Using polygenic scores (PGS), we investigate the prospective direction involved in suboptimal sleep durations and depression. Male and female participants, aged ≥50, were recruited from the English Longitudinal Study of Ageing (ELSA). PGS for sleep duration, short-sleep, and long-sleep were calculated using summary statistics data from the UK Biobank cohort. Sleep duration, categorised into short-sleep ("≤5 h"), optimal-sleep (">5 to <9 h"), and long-sleep ("≥9 h"), was measured at baseline and across an average 8-year follow-up. Subclinical depression (Centre for Epidemiological Studies Depression Scale [≥4 of 7]) was also ascertained at baseline and across an average 8-year follow-up. One standard deviation increase in PGS for short-sleep was associated with 14% higher odds of depression onset (95% CI = 1.03-1.25, p = 0.008). However, PGS for sleep duration (OR = 0.92, 95% CI = 0.84-1.00, p = 0.053) and long-sleep (OR = 0.97, 95% CI = 0.89-1.06, p = 0.544) were not associated with depression onset during follow-up. During the same period, PGS for depression was not associated with overall sleep duration, short-sleep, or long-sleep. Polygenic predisposition to short-sleep was associated with depression onset over an average 8-year period. However, polygenic predisposition to depression was not associated with overall sleep duration, short-sleep or long-sleep, suggesting different mechanisms underlie the relationship between depression and the subsequent onset of suboptimal sleep durations in older adults.

Genome-wide association studies and cross-population meta-analyses investigating short and long sleep duration

Sleep duration has been linked to a wide range of negative health outcomes and to reduced life expectancy. We present genome-wide association studies of short ( ≤ 5 h) and long ( ≥ 10 h) sleep duration in adults of European (N = 445,966), African (N = 27,785), East Asian (N = 3141), and admixed-American (N = 16,250) ancestry from UK Biobank and the Million Veteran Programme. In a cross-population meta-analysis, we identify 84 independent loci for short sleep and 1 for long sleep. We estimate SNP-based heritability for both sleep traits in each ancestry based on population derived linkage disequilibrium (LD) scores using cov-LDSC. We identify positive genetic correlation between short and long sleep traits (rg = 0.16 ± 0.04; p = 0.0002), as well as similar patterns of genetic correlation with other psychiatric and cardiometabolic phenotypes. Mendelian randomisation reveals a directional causal relationship between short sleep and depression, and a bidirectional causal relationship between long sleep and depression.

Multi-ancestry genome-wide analysis identifies shared genetic effects and common genetic variants for self-reported sleep duration

Both short (≤6 h per night) and long sleep duration (≥9 h per night) are associated with increased risk of chronic diseases. Despite evidence linking habitual sleep duration and risk of disease, the genetic determinants of sleep duration in the general population are poorly understood, especially outside of European (EUR) populations. Here, we report that a polygenic score of 78 European ancestry sleep duration single-nucleotide polymorphisms (SNPs) is associated with sleep duration in an African (n = 7288; P = 0.003), an East Asian (n = 13 618; P = 6 × 10-4) and a South Asian (n = 7485; P = 0.025) genetic ancestry cohort, but not in a Hispanic/Latino cohort (n = 8726; P = 0.71). Furthermore, in a pan-ancestry (N = 483 235) meta-analysis of genome-wide association studies (GWAS) for habitual sleep duration, 73 loci are associated with genome-wide statistical significance. Follow-up of five loci (near HACD2, COG5, PRR12, SH3RF1 and KCNQ5) identified expression-quantitative trait loci for PRR12 and COG5 in brain tissues and pleiotropic associations with cardiovascular and neuropsychiatric traits. Overall, our results suggest that the genetic basis of sleep duration is at least partially shared across diverse ancestry groups.

What daily factors affect the sleep habits of Japanese toddlers?

STUDY OBJECTIVES

Good sleep, especially during early childhood, is important for development. In Japan, the mean nocturnal sleep duration of toddlers is < 10 hours, and even if toddlers slept for > 11 hours/day, as recommended by the National Sleep Foundation, some of them showed late bedtime and late wake-up time or took long naps. Therefore, we provisionally assumed the minimal sleep conditions for Japanese toddlers, named Nenne-criteria, such as bedtime before 10:00 pm, nocturnal sleep duration of ≥ 9 hours, and < 1 average time of awakening after sleep onset, and investigated the important factors for good sleep.

METHODS

We analyzed cross-sectional data from online surveys describing the sleep-related behaviors of 2,124 toddlers and their caregivers. We compared the daily schedules that affect sleep between the Nenne-criteria-meet group and the not-meet group.

RESULTS

The Nenne-criteria-meet group showed better daytime behaviors than the not-meet group. Structural equation modeling on daily schedules revealed that, to increase sleep pressure at the appropriate time, it is important to restrict media viewing, play outdoors in the morning, have an early nap ending time, avoid hyperarousal-inducing behaviors before bedtime, maintain daily schedules regularly, and decrease social jetlag.

CONCLUSIONS

The Nenne-criteria are useful for screening Japanese toddlers who require intervention for sleep hygiene. To improve toddlers' sleep, it is important not only to guide the ideal bedtime but also to provide tips for improving daily schedules and to avoid suboptimal sleep-related behaviors.

CITATION

Murata E, Yoshizaki A, Fujisawa TX, Tachibana M, Taniike M, Mohri I. What daily factors affect the sleep habits of Japanese toddlers? J Clin Sleep Med. 2023;19(6):1089-1101.

Circadian Rhythm Sleep Disorders: Genetics, Mechanisms, and Adverse Effects on Health

Nearly all living organisms, from cyanobacteria to humans, have an internal circadian oscillation with a periodicity of approximately 24 h. In mammals, circadian rhythms regulate diverse physiological processes including the body temperature, energy metabolism, immunity, hormone secretion, and daily sleep-wake cycle. Sleep is tightly regulated by circadian rhythms, whereas a misalignment between the circadian rhythms and external environment may lead to circadian rhythm sleep disorders (CRSD). CRSD includes four main kinds of disorders: the advanced sleep-wake phase disorder (ASPD), the delayed sleep-wake phase disorder (DSPD), the irregular sleep-wake rhythm disorder and the non-24-h sleep-wake rhythm disorder. Recent studies have begun to shed light on the genetic basis of CRSD. Deciphering the genetic codes for ASPD and DSPD has so far been more successful than the other CRSDs, which allow for the development of animal models and understanding of the pathological mechanisms for these disorders. And studies from humans or animal models implicate CRSDs are associated with adverse health consequences, such as cancer and mental disorders. In this review, we will summarize the recent advances in the genetics, underlying mechanisms and the adverse effects on health of ASPD and DSPD.

Shift work tolerance

BACKGROUND

Shift work is widespread due to 24-h work in many occupations. Understanding differences in individual shift work tolerance (SWT) can help develop coping strategies for shift workers.

AIMS

This in-depth qualitative review elucidates the architecture of SWT, providing an overview of the research advances in the last decade (2011-2021).

METHODS

We searched Google Scholar, PubMed and Medline for different word combinations concerning SWT. Genome-wide association studies (GWAS) for the potential genetic basis of SWT were additionally searched in GWAS Central and GWAS Catalogue.

RESULTS

Eleven new studies were published since 2011, with the proportion of longitudinal studies on SWT having more than doubled in the past decade. They consolidate prior findings (e.g. hardiness most consistently associated with SWT) and discovered additional aspects of SWT like resistance to change and job stress. The 15 large-scale GWAS identified, most of which using UK Biobank (UKB) and 23andMe data, involved mapped genes showing overlap especially within analysis of the same phenotype (e.g. PER2/3 for morningness, PAX8 for sleep duration and LINGO1 for neuroticism). Individual GWAS for additional traits such as resilience have also been published though assessments of gene overlap are not yet possible.

CONCLUSIONS

Progress regarding longitudinal studies on SWT has been made though a more consistent definition of SWT remains crucial for future research. Non-genetic studies on SWT suggest several important traits and factors; many of which have now also been explored using GWAS. Such evidence could serve as basis for individualized risk prediction and disease prevention approaches for night-shift workers.

The dihydropyrimidine dehydrogenase gene contributes to heritable differences in sleep in mice

Many aspects of sleep are heritable, but only a few sleep-regulating genes have been reported. Here, we leverage mouse models to identify and confirm a previously unreported gene affecting sleep duration-dihydropyrimidine dehydrogenase (Dpyd). Using activity patterns to quantify sleep in 325 Diversity Outbred (DO) mice-a population with high genetic and phenotypic heterogeneity-a linkage peak for total sleep in the active lights off period was identified on chromosome 3 (LOD score = 7.14). Mice with the PWK/PhJ ancestral haplotype at this location demonstrated markedly reduced sleep. Among the genes within the linkage region, available RNA sequencing data in an independent sample of DO mice supported a highly significant expression quantitative trait locus for Dpyd, wherein reduced expression was associated with the PWK/PhJ allele. Validation studies were performed using activity monitoring and EEG/EMG recording in Collaborative Cross mouse strains with and without the PWK/PhJ haplotype at this location, as well as EEG and EMG recording of sleep and wake in Dpyd knockout mice and wild-type littermate controls. Mice lacking Dpyd had 78.4 min less sleep during the lights-off period than wild-type mice (p = 0.007; Cohen's d = -0.94). There was no difference in other measured behaviors in knockout mice, including assays evaluating cognitive-, social-, and affective-disorder-related behaviors. Dpyd encodes the rate-limiting enzyme in the metabolic pathway that catabolizes uracil and thymidine to β-alanine, an inhibitory neurotransmitter. Thus, data support β-alanine as a neurotransmitter that promotes sleep in mice.

Ischemic Stroke and Sleep: The Linking Genetic Factors

This review summarizes the available data about genetic factors which can link ischemic stroke and sleep. Sleep patterns (subjective and objective measures) are characterized by heritability and comprise up to 38-46%. According to Mendelian randomization analysis, genetic liability for short sleep duration and frequent insomnia symptoms is associated with ischemic stroke (predominantly of large artery subtype). The potential genetic links include variants of circadian genes, genes encoding components of neurotransmitter systems, common cardiovascular risk factors, as well as specific genetic factors related to certain sleep disorders.

Characteristics associated with hypersomnia and excessive daytime sleepiness identified by extended polysomnography recording

STUDY OBJECTIVES

Hypersomnolence, defined by excessive daytime sleepiness (EDS) or excessive quantity of sleep (EQS), has been associated with increased morbidity. The aim of this study was to determine the clinical and polysomnographic characteristics associated with EQS and EDS assessed objectively during extended polysomnography recording.

METHODS

A total of 266 drug-free subjects (201 women; mean age: 26.5 years [16.08; 60.87]) underwent 32-h bed-rest polysomnography recording preceded by polysomnography and modified multiple sleep latency test (mMSLT). Participants were categorized according to their total sleep time (bed-rest TST ≥19 h, hypersomnia), objective EDS (mean sleep latency on MSLT ≤8 min), and self-reported EDS (Epworth sleepiness scale score >10) and EQS (≥9 h/24 h per week).

RESULTS

Subjects with hypersomnia were often younger, with normal sleep architecture, high nighttime sleep efficiency, and severe objective EDS. No association with sex, body mass index, Epworth sleepiness scale, EQS, and depressive symptoms was detected. Subjects with objective EDS had less EQS, higher sleep efficiency, and increased hypersomnia. Discrepancies were observed between objective and self-reported measures of sleep duration and EDS. Finally, 71 subjects were identified who had objective hypersomnia and/or EDS, no medical and psychiatric conditions and normal polysomnography parameters, and therefore met the stringent criteria of idiopathic hypersomnia, an orphan disorder.

CONCLUSIONS

Sleep duration and EDS should be quantified using self-reported and objective measures in a controlled procedure to differentiate long sleepers, patients with hypersomnia, and patients with idiopathic hypersomnia. This will help to better understand their biology, to identify specific biomarkers, and to assess related health outcomes.

Shared genetic architecture underlying sleep and weight in children

Meta-analyses suggest shorter sleep as a risk factor for obesity in children. The prevailing hypothesis is that shorter sleep causes obesity by impacting homeostatic processes. Sleep duration and adiposity are both heritable, and the association may reflect shared genetic aetiology. We examined the association between a body mass index (BMI) genetic risk score (GRS) and objectively-measured total sleep time (TST) in a cohort of Norwegian children (enrolled at age four in 2007-2008) using cross-sectional data at age six. The analytical sample included 452 six-year old children with complete genotype and phenotype data. The outcome was actigraphic total sleep time (TST) measured at age six years. Genetic risk of obesity was inferred using a 32-single nucleotide polymorphism (SNP) weighted GRS of BMI. Covariates were BMI-Standard deviation scores (SDS) (which takes into account age and sex) and, in a sensitivity analysis socioeconomic status. Analyses consisted of Pearson's correlations and linear regressions. In our sample, 54% of participants were male; mean (SD) TST, age and BMI were 9.6 (0.8) hours, 6.0 (0.2) years and 15.3 (1.2) kg/m², respectively. BMI and TST were not correlated, r = -0.003, p = 0.946. However, the BMI GRS was associated with TST after adjusting for BMI-SDS, standardised β = -0.11; 95% confidence interval (CI) = -0.22, -0.01. To our knowledge, this is the first study to establish a relationship between genetic risk of obesity and objective sleep duration in children. Findings suggest some shared genetic aetiology underlying these traits. Future research could identify the common biological pathways through which common genes predispose to both shorter sleep and increased risk of obesity.

Spindles are highly heritable as identified by different spindle detectors

STUDY OBJECTIVES

Sleep spindles, a defining feature of stage N2 sleep, are maximal at central electrodes and are found in the frequency range of the electroencephalogram (EEG) (sigma 11-16 Hz) that is known to be heritable. However, relatively little is known about the heritability of spindles. Two recent studies investigating the heritability of spindles reported moderate heritability, but with conflicting results depending on scalp location and spindle type. The present study aimed to definitively assess the heritability of sleep spindle characteristics.

METHODS

We utilized the polysomnography data of 58 monozygotic and 40 dizygotic same-sex twin pairs to identify heritable characteristics of spindles at C3/C4 in stage N2 sleep including density, duration, peak-to-peak amplitude, and oscillation frequency. We implemented and tested a variety of spindle detection algorithms and used two complementary methods of estimating trait heritability.

RESULTS

We found robust evidence to support strong heritability of spindles regardless of detector method (h2 > 0.8). However not all spindle characteristics were equally heritable, and each spindle detection method produced a different pattern of results.

CONCLUSIONS

The sleep spindle in stage N2 sleep is highly heritable, but the heritability differs for individual spindle characteristics and depends on the spindle detector used for analysis.

Is COVID-19 Keeping us Up at Night? Stress, Anxiety, and Sleep Among Adult Twins

In response to the COVID-19 pandemic, a variety of social distancing measures to mitigate the virus outbreak have been implemented. These measures may have unintended consequences on individuals' well-being, such as increased stress, anxiety, and sleep disruptions. We investigated the extent to which individuals' mental health status is associated with perceived changes in sleep amount and sleep quality among a sample of adult twin pairs (N = 909 pairs; 77% MZ, 23% DZ), less than a month after the outbreak was declared a pandemic by the World Health Organization. About half of participants reported no change in sleep amount (50.1%) or sleep quality (55.6%). Approximately one-third of the participants had increased amount of sleep (29.8%), and 32.9% reported a decrease in sleep quality. We found that stress and anxiety levels were associated with sleep reduction (ORs = 2.36 and 3.12 for stress and anxiety, respectively) and poorer sleep quality (ORs = 2.45 and 3.73 for stress and anxiety, respectively), even after taking into account between-family confounds. A much smaller association was observed between levels of stress and anxiety and increased sleep amount (ORs = 1.42 and 1.60 for stress and anxiety, respectively) and sleep quality (OR = 1.21 and 1.29 for stress and anxiety, respectively), which was no longer significant after controlling for between-family confounds. Our results demonstrate that stress and anxiety associated with the COVID-19 pandemic and social distancing measures may be linked to reduced sleep amount and quality.

Heritability of sleep duration and quality: A systematic review and meta-analysis

Epidemiological and interventional research has highlighted sleep as a potentially modifiable risk factor associated with poor physical and mental health. Emerging evidence from (behavioral) genetic research also shows that sleep characteristics are under strong genetic control. With this study we aimed to meta-analyze the literature in this area to quantify the heritability of sleep duration and sleep quality in the general population. We conducted a systematic literature search in five online databases on January 24th 2020. Two authors independently screened 5644 abstracts, and 160 complete articles for the inclusion criteria of twin studies from the general population reporting heritability statistics on sleep duration and/or quality, and written in English. We ultimately included 23 papers (19 independent samples: 45,328 twins between 6 mo and 88 y) for sleep duration, and 13 papers (10 independent samples: 39,020 twins between 16 and 95 y) for sleep quality. Collectively, we showed that 46% of the variability in sleep duration and 44% of the variability in sleep quality is genetically determined. The remaining variation in the sleep characteristics can mostly be attributed to the unique environment the twins experience, although the shared environment seemed to play a role for the variability of childhood sleep duration. Meta-analyzed heritability estimates for sleep duration, however, varied substantially with age (17% infancy, 20-52% childhood, 69% adolescence and 42-45% adulthood) and reporter (8% parent-report, 38-52% self-report). Heritability estimates for actigraphic and Polysomnography (PSG)-estimated sleep were based on few small samples, warranting more research. Our findings highlight the importance of considering genetic influences when aiming to understand the underlying mechanisms contributing to the trajectories of sleep patterns across the lifespan.

The heritability of insomnia: Systematic review and meta-analysis of twin studies

Twin studies have consistently found that genetic factors explain a substantial proportion of the variance for insomnia. However, studies vary widely in their heritability estimates. Therefore, this meta-analysis aimed to: 1) Estimate the mean heritability of insomnia; 2) Assess heterogeneity among twin studies of insomnia; and 3) Search and analyse characteristics of the studies (moderator variables) that may explain heterogeneity among estimates. For this purpose, separate meta-analyses were carried out for MZ and DZ correlations and for heritability estimates by assuming random-effects models. Thirteen independent samples were included in this meta-analysis. The heterogeneity index for heritability estimates was significant in both best fitting models (I² = 98.77, P < .0001) and full models (I² = 97.80, P < .0001). MZ correlations were higher (0.37; 95%CI: 0.31,.43) than DZ correlations (0.15; 95%CI: 0.12,.18). A mean heritability of 0.39 (95%CI: 0.32,.44) was found for insomnia. These results highlight the role of genetic factors in explaining differences among the population on insomnia and Emphasize heterogeneity among studies. Further research is needed to identify variables that could explain this heterogeneity.

Sleep duration: A review of genome-wide association studies (GWAS) in adults from 2007 to 2020

A modest body of research exists in the area of human sleep genetics, which suggests that specific sleep phenotypes are, like many other complex traits, somewhat heritable. Until 2007 research into sleep genetics relied solely on twin studies, but in the last 13 years with the advent of huge biobanks and very large-scale genome-wide association studies, the field of molecular sleep genetics has seen important advances. To date, the majority have focused on self-reported sleep duration, but in recent years genome-wide association studies of objectively-measured sleep have emerged. These genetic studies have discovered multiple common genetic variants and as such, have provided insight into potential biological pathways, causal relationships between sleep duration and important disease outcomes using Mendelian randomisation. They have also shown that the heritability of these traits may not be as high as previously estimated. This article is the first to provide a detailed review of these recent advances in the genetic epidemiology of sleep duration. Studies were identified using both the GWAS Catalog and PubMed for completeness. Focus is on the genome-wide association studies published to date, including whether and how they have elucidated important biology and advanced knowledge in the area of sleep and health.

Natural selection on sleep duration in Drosophila melanogaster

Sleep is ubiquitous across animal species, but why it persists is not well understood. Here we observe natural selection act on Drosophila sleep by relaxing bi-directional artificial selection for extreme sleep duration for 62 generations. When artificial selection was suspended, sleep increased in populations previously selected for short sleep. Likewise, sleep decreased in populations previously selected for long sleep when artificial selection was relaxed. We measured the corresponding changes in the allele frequencies of genomic variants responding to artificial selection. The allele frequencies of these variants reversed course in response to relaxed selection, and for short sleepers, the changes exceeded allele frequency changes that would be expected under random genetic drift. These observations suggest that the variants are causal polymorphisms for sleep duration responding to natural selection pressure. These polymorphisms may therefore pinpoint the most important regions of the genome maintaining variation in sleep duration.

The heritability of insomnia: A meta-analysis of twin studies

Twin studies of insomnia exhibit heterogeneity in estimates of heritability. This heterogeneity is likely because of sex differences, age of the sample, the reporter and the definition of insomnia. The aim of the present study was to systematically search the literature for twin studies investigating insomnia disorder and insomnia symptoms and to meta-analyse the estimates of heritability derived from these studies to generate an overall estimate of heritability. We further examined whether heritability was moderated by sex, age, reporter and insomnia symptom. A systematic literature search of five online databases was completed on 24 January 2020. Two authors independently screened 5644 abstracts, and 160 complete papers for the inclusion criteria of twin studies from the general population reporting heritability statistics on insomnia or insomnia symptoms, written in English, reporting data from independent studies. We ultimately included 12 papers in the meta-analysis. The meta-analysis focussed on twin intra-class correlations for monozygotic and dizygotic twins. Based on these intra-class correlations, the meta-analytic estimate of heritability was estimated at 40%. Moderator analyses showed stronger heritability in females than males; and for parent-reported insomnia symptoms compared with self-reported insomnia symptoms. There were no other significant moderator effects, although this is likely because of the small number of studies that were comparable across levels of the moderators. Our meta-analysis provides a robust estimate of the heritability of insomnia, which can inform future research aiming to uncover molecular genetic factors involved in insomnia vulnerability.

Perceived Stress and Sleep Quality in Midlife and Later: Controlling for Genetic and Environmental Influences

OBJECTIVE/BACKGROUND

Stress is a strong predictor for poor sleep quality. However, little is known about the mechanism of this association or the respective contribution of genetic and environmental factors. This study aims to investigate general distress as a mediator and cognitive/emotional control as a moderator in the stress-sleep relationship and estimate the influence of gene and environment in this mechanism using a national representative sample.

PARTICIPANTS

1,255 middle-aged and elderly Americans and a subset of 296 twins.

METHODS

The Pittsburgh Sleep Quality Index, the Perceived Stress Scale, the Mood and Anxiety Symptom Questionnaire and the Self-Control Scale assessed sleep quality, perceived stress, general distress, and emotional/cognitive control. Structural equation modeling was used to test the mediating and moderating effect. ACE models on MZ and DZ twins were used to separate the contribution of genetic and environmental factors. Finally, a co-twin design was nested in the SEM to control for the genetic and familial confounds in the stress-sleep relationship.

RESULTS

General distress mediated the relationship between stress and sleep while emotional/cognitive control buffered the impact of stress on general distress. 7.69% of the variance in sleep quality was explained by genetic and familial factors and 8.26% was explained by individual-specific factors. Emotional/cognitive control only moderated the individual-specific association between stress and sleep.

CONCLUSIONS

Gene/family factors and individual factors explained an equivalent proportion of the stress-sleep relationship. The genetic and familial association between stress and sleep is more robust, whereas the individual-specific association can be buffered by regulation strategies.

Generational changes in young adults' sleep duration: a prospective analysis of mother-offspring dyads

OBJECTIVE

To quantify the changes in sleep duration over two generations of young adults.

METHODS

We used data from the Mater-University of Queensland Study of Pregnancy cohort to compare sleep duration in mother and offspring. The analyses were restricted to 1,731 mothers who were young adults (mean age 21.96 years; SD±1.90) at the baseline measurement, and their offspring who were about the same age (mean age 20.6 years; SD±0.86) when assessed 21 years later. Maternal sleep was explored by asking the mother, during the first trimester, about her typical sleep duration prior to pregnancy, while offspring participants were asked about the sleep duration in the last month at the time assessed. Multinomial logistic regression for correlated responses was used to assess generational changes.

RESULTS

We found that offspring had 3.2 (2.7, 3.9) times the odds of sleeping for short duration (≤6 hours/night) and 1.7 (1.5, 1.9) times the odds of sleeping for a longer duration (≥9 hours/night) compared with their mothers. Gender-based analysis found that daughters had 3.0 (2.3, 5.0) times the odds of sleeping for a short duration, while sons had 3.4 (2.6, 6.4) times the odds of sleeping for a short duration compared with their mothers.

CONCLUSIONS

There is a significant decline in sleep duration below recommendations as well as a substantial increase in long-duration above the recommendations over two generations of young adults. Therefore, the focus of sleep health should not be limited to short sleep, but on the need for achieving optimal sleep recommended for the age.

A missense variant in PER2 is associated with delayed sleep-wake phase disorder in a Japanese population

Delayed sleep-wake phase disorder (DSWPD) is a subtype of circadian rhythm sleep-wake disorders, and is characterized by an inability to fall asleep until late at night and wake up at a socially acceptable time in the morning. The study aim was to identify low-frequency nonsense and missense variants that are associated with DSWPD. Candidate variants in circadian rhythm-related genes were extracted by integration of genetic variation databases and in silico assessment. We narrowed down the candidates to six variants. To examine whether the six variants are associated with DSWPD, we performed an association study in 236 Japanese patients with DSWPD and 1436 controls. A low-frequency missense variant (p.Val1205Met) in PER2 showed a significant association with DSWPD (2.5% in cases and 1.1% in controls, P = 0.026, odds ratio (OR) = 2.32). The variant was also associated with idiopathic hypersomnia known to have a tendency toward phase delay (P = 0.038, OR = 2.07). PER2 forms a heterodimer with CRY, and the heterodimer plays an important role in the regulation of circadian rhythms. Val1205 is located in the CRY-binding domain of PER2 and was hypothesized to interact with CRY. The p.Val1205Met substitution could be a potential genetic marker for DSWPD.

Self-Reported Sleep Duration and Pattern in Old Order Amish and Non-Amish Adults

STUDY OBJECTIVES

We hypothesized that sleep duration in the Amish would be longer than in non-Amish.

METHODS

Sleep duration was obtained by questionnaire administered to Amish individuals (n = 3,418) and from the 2015-2016 National Health and Nutrition Examination Survey (NHANES; n = 1,912). Self-reported sleep duration was calculated as the difference in usual times that the participants went to bed at night and woke up in the morning.

RESULTS

In Amish (43.7 ± 16.7 years) and NHANES (50.0 ± 20.6 years), women had a longer sleep duration than men (P < .0001 in both groups) and sleep was significantly longer in those aged 18-29 years and ≥ 70 years, compared to those aged 30-69 years. Seasonal-adjusted sleep duration was shorter in Amish than that in NHANES (7.8 minutes shorter, age- and sex-adjusted P < .0001). However, Amish were less likely to report sleeping fewer than 7 hours per night (15.4% in Amish versus 20.5% in NHANES, P < .0001). Amish went to bed 80.4 minutes earlier than NHANES and arose 87.6 minutes earlier (age-, sex-, and season-adjusted P < .0001 for both). In the Amish, sleep duration was longer in clerks than in farmers (P < .0001) and was significantly correlated among household members (.15 < r < .62, P < .001), although there was no evidence that this trait was heritable (h² approximately 0) after adjustment for household.

CONCLUSIONS

The lower frequency of short sleepers in the Amish may contribute to the relatively lower risks of cardiometabolic diseases observed in this population.

CITATION

Zhang M, Ryan KA, Wickwire E, Postolache TT, Xu H, Daue M, Snitker S, Pollin TI, Shuldiner AR, Mitchell BD. Self-reported sleep duration and pattern in old order amish and non-amish adults. J Clin Sleep Med. 2019;15(9):1321-1328.

Efficacy of individualized homeopathic treatment of insomnia: Double-blind, randomized, placebo-controlled clinical trial

BACKGROUND

Insomnia is the most common sleep-related complaint associated with impaired day-time functioning, reduced quality of life, increased morbidity and substantial societal cost. We evaluated whether individualized homeopathy (IH) could produce significant effect beyond placebo in treatment of insomnia.

METHODS

In this double-blind, randomized, placebo-controlled, two parallel arms trial, 60 patients were randomized to receive either IH/verum or control/placebo (1:1). Patient-administered sleep diary (6 items; 1: latency to fall asleep, 2: minutes awake in middle of night, 3: minutes awake too early, 4: hours spent in bed, 5: total sleep time in hours, and 6: sleep efficiency) and Insomnia Severity Index (ISI) were taken as the primary and secondary outcomes respectively, measured at baseline, and after 3 months.

RESULTS

Five patients dropped out (verum: 2, control: 3). Intention to treat sample (n = 60) was analyzed. Trial arms were comparable at baseline. In the verum group, except sleep diary item 3 (P =  0.371), rest of the outcomes improved significantly (all P < 0.01). In the control group, there were significant improvements in diary item 6 and ISI score (P < 0.01) and just significant improvement in item 5 (P =  0.018). Group differences were significant for items 4, 5 and 6 (P < 0.01) and just significant (P =  0.014) for ISI score with moderate to large effect sizes; but non-significant (P > 0.01) for rest of the outcomes.

CONCLUSION

IH seemed to produce significantly better effect than placebo. Rigorous trials and independent replications are warranted.

Heritability of the timing of food intake

BACKGROUND & AIMS

While environmental factors are presumed to be primary drivers of food timing, preliminary evidence suggests that genetics may be an additional determinant. The aim was to explore the relative contribution of genetics and environmental factors to variation in the timing of food intake in a Spanish twin population. Because chronotype, bedtime and wake time are related to food timing, covariance with food timing was further assessed.

METHODS

In this observational study, 53 pairs of adult (mean (SD) = 52 (6.03) years) female twins (28 monozygotic; 25 dizygotic) were recruited from the Murcia Twin Register. Zygosity was determined by DNA-testing. Timing of the three main meals of the day was assessed via 7-day dietary records, and the midpoint of food intake was computed by calculating the midpoint between breakfast and dinner times. Chronotype, bedtime and wake time were self-reported. Heritability of food timing and related traits were estimated by comparing monozygotic and dizygotic twin correlations and fitting genetic structural equation models to measured variables.

RESULTS

We observed genetic influences for food timing, with highest heritability for the midpoint of food intake (64%) in an overweight/obese population (BMI = 26.01 ± 3.77). Genetic factors contributed to a higher degree to the timing of breakfast (56%) than the timing of lunch (38%) or dinner (n.s.). Similarly, heritability estimates were larger in related behavioral traits earlier on in the day (i.e. wake time, (55%)), than those later on in the day (i.e. bedtime, (38%)). Bivariate analyses revealed a significant genetic overlap between food timing and bedtime and chronotype (rG between 0.78 and 0.91).

CONCLUSIONS

Genetic influences appear to account for a significant proportion of the variability in food timing, particularly breakfast. Thus, interventions related to food timing may be more effective when targeting afternoon/evening traits, such as lunch or dinner times. Furthermore, our data suggest shared genetic architecture underlying food timing and phenotypically related traits.

CLINICAL TRIAL

NCT03059576. https://clinicaltrials.gov/ct2/show/NCT03059576.

Genome-wide association study identifies genetic loci for self-reported habitual sleep duration supported by accelerometer-derived estimates

Sleep is an essential state of decreased activity and alertness but molecular factors regulating sleep duration remain unknown. Through genome-wide association analysis in 446,118 adults of European ancestry from the UK Biobank, we identify 78 loci for self-reported habitual sleep duration (p < 5 × 10⁻⁸; 43 loci at p < 6 × 10⁻⁹). Replication is observed for PAX8, VRK2, and FBXL12/UBL5/PIN1 loci in the CHARGE study (n = 47,180; p < 6.3 × 10⁻⁴), and 55 signals show sign-concordant effects. The 78 loci further associate with accelerometer-derived sleep duration, daytime inactivity, sleep efficiency and number of sleep bouts in secondary analysis (n = 85,499). Loci are enriched for pathways including striatum and subpallium development, mechanosensory response, dopamine binding, synaptic neurotransmission and plasticity, among others. Genetic correlation indicates shared links with anthropometric, cognitive, metabolic, and psychiatric traits and two-sample Mendelian randomization highlights a bidirectional causal link with schizophrenia. This work provides insights into the genetic basis for inter-individual variation in sleep duration implicating multiple biological pathways.

Sleep is essential for homeostasis and insufficient or excessive sleep are associated with adverse outcomes. Here, the authors perform GWAS for self-reported habitual sleep duration in adults, supported by accelerometer-derived measures, and identify genetic correlation with psychiatric and metabolic traits

Genome-wide analysis of insomnia disorder

Insomnia is a worldwide problem with substantial deleterious health effects. Twin studies have shown a heritable basis for various sleep-related traits, including insomnia, but robust genetic risk variants have just recently begun to be identified. We conducted genome-wide association studies (GWAS) of soldiers in the Army Study To Assess Risk and Resilience in Servicemembers (STARRS). GWAS were carried out separately for each ancestral group (EUR, AFR, LAT) using logistic regression for each of the STARRS component studies (including 3,237 cases and 14,414 controls), and then meta-analysis was conducted across studies and ancestral groups. Heritability (SNP-based) for lifetime insomnia disorder was significant (h²_g = 0.115, p = 1.78 × 10^-4 in EUR). A meta-analysis including three ancestral groups and three study cohorts revealed a genome-wide significant locus on Chr 7 (q11.22) (top SNP rs186736700, OR = 0.607, p = 4.88 × 10^-9) and a genome-wide significant gene-based association (p = 7.61 × 10^-7) in EUR for RFX3 on Chr 9. Polygenic risk for sleeplessness/insomnia severity in UK Biobank was significantly positively associated with likelihood of insomnia disorder in STARRS. Genetic contributions to insomnia disorder in STARRS were significantly positively correlated with major depressive disorder (r_g = 0.44, se = 0.22, p = 0.047) and type 2 diabetes (r_g = 0.43, se = 0.20, p = 0.037), and negatively with morningness chronotype (r_g = -0.34, se = 0.17, p = 0.039) and subjective well being (r_g = -0.59, se = 0.23, p = 0.009) in external datasets. Insomnia associated loci may contribute to the genetic risk underlying a range of health conditions including psychiatric disorders and metabolic disease.

Pathway-based analysis of genome-wide association study of circadian phenotypes

Sleepiness affects normal social life, which attracts more and more attention. Circadian phenotypes contribute to obvious individual differences in susceptibility to sleepiness. We aimed to identify candidate single nucleotide polymorphisms (SNPs) which may cause circadian phenotypes, elucidate the potential mechanisms, and generate corresponding SNP-gene-pathways. A genome-wide association studies (GWAS) dataset of circadian phenotypes was utilized in the study. Then, the Identify Candidate Causal SNPs and Pathways analysis was employed to the GWAS dataset after quality control filters. Furthermore, genotype-phenotype association analysis was performed with HapMap database. Four SNPs in three different genes were determined to correlate with usual weekday bedtime, totally providing seven hypothetical mechanisms. Eleven SNPs in six genes were identified to correlate with usual weekday sleep duration, which provided six hypothetical pathways. Our results demonstrated that fifteen candidate SNPs in eight genes played vital roles in six hypothetical pathways implicated in usual weekday bedtime and six potential pathways involved in usual weekday sleep duration.

Prospective study of chronotype and incident depression among middle- and older-aged women in the Nurses' Health Study II

BACKGROUND

Prior cross-sectional studies have suggested that being a late chronotype is associated with depression and depressive symptoms, but prospective data are lacking.

METHODS

We examined the association between chronotype and incident depression (defined as self-reported physician/clinician-diagnosed depression or antidepressant medication use) in 32,470 female participants of the Nurses' Health Study II cohort who self-reported their chronotype (early, intermediate or late) and were free of depression at baseline in 2009 (average age: 55 yrs). Women updated their depression status on biennial questionnaires in 2011 and 2013. We used multivariable (MV)-adjusted Cox proportional hazards models to estimate hazard ratios (HR) and 95% confidence intervals (95%CI) for incident depression across chronotype categories (i.e., early, intermediate, and late chronotypes).

RESULTS

Across a follow-up period of 4 years, we observed 2,581 cases of incident depression in this cohort. Compared to intermediate chronotypes, early chronotypes had a modestly lower risk of depression after MV adjustment (MVHR = 0.88, 95%CI = 0.81-0.96), whereas late chronotypes had a similar risk of 1.06 (95%CI = 0.93-1.20); the overall trend across chronotype categories was statistically significant (ptrend<0.01). Results were similar when we restricted analyses to women who reported average sleep durations (7-8 h/day) and no history of rotating night shift work at baseline.

CONCLUSIONS

Our results suggest that chronotype may influence the risk of depression in middle-to older-aged women. Additional studies are needed to confirm these findings and examine roles of both environmental and genetic factors to further our understanding of the role of chronotype in the etiology of mood disorders.

Quantifying sleep architecture dynamics and individual differences using big data and Bayesian networks

The pattern of sleep stages across a night (sleep architecture) is influenced by biological, behavioral, and clinical variables. However, traditional measures of sleep architecture such as stage proportions, fail to capture sleep dynamics. Here we quantify the impact of individual differences on the dynamics of sleep architecture and determine which factors or set of factors best predict the next sleep stage from current stage information. We investigated the influence of age, sex, body mass index, time of day, and sleep time on static (e.g. minutes in stage, sleep efficiency) and dynamic measures of sleep architecture (e.g. transition probabilities and stage duration distributions) using a large dataset of 3202 nights from a non-clinical population. Multi-level regressions show that sex effects duration of all Non-Rapid Eye Movement (NREM) stages, and age has a curvilinear relationship for Wake After Sleep Onset (WASO) and slow wave sleep (SWS) minutes. Bayesian network modeling reveals sleep architecture depends on time of day, total sleep time, age and sex, but not BMI. Older adults, and particularly males, have shorter bouts (more fragmentation) of Stage 2, SWS, and they transition less frequently to these stages. Additionally, we showed that the next sleep stage and its duration can be optimally predicted by the prior 2 stages and age. Our results demonstrate the potential benefit of big data and Bayesian network approaches in quantifying static and dynamic architecture of normal sleep.

Three-dimensional photography for the evaluation of facial profiles in obstructive sleep apnoea

BACKGROUND AND OBJECTIVE

Craniofacial structure is an important determinant of obstructive sleep apnoea (OSA) syndrome risk. Three-dimensional stereo-photogrammetry (3dMD) is a novel technique which allows quantification of the craniofacial profile. This study compares the facial images of OSA patients captured by 3dMD to three-dimensional computed tomography (3-D CT) and two-dimensional (2-D) digital photogrammetry. Measurements were correlated with indices of OSA severity.

METHODS

Thirty-eight patients diagnosed with OSA were included, and digital photogrammetry, 3dMD and 3-D CT were performed. Distances, areas, angles and volumes from the images captured by three methods were analysed.

RESULTS

Almost all measurements captured by 3dMD showed strong agreement with 3-D CT measurements. Results from 2-D digital photogrammetry showed poor agreement with 3-D CT. Mandibular width, neck perimeter size and maxillary volume measurements correlated well with the severity of OSA using all three imaging methods. Mandibular length, facial width, binocular width, neck width, cranial base triangle area, cranial base area 1 and middle cranial fossa volume correlated well with OSA severity using 3dMD and 3-D CT, but not with 2-D digital photogrammetry.

CONCLUSION

3dMD provided accurate craniofacial measurements of OSA patients, which were highly concordant with those obtained by CT, while avoiding the radiation associated with CT.

Disorders of sleep and circadian rhythms

Sleep is fundamental to the survival of humans. However, knowledge regarding the role of sleep and its regulation is poorly understood. Genetics in flies, mice, and humans has led to a detailed understanding of some aspects of circadian regulation. Sleep homeostasis (the effect of increasing periods of wakefulness on our sleep propensity) is largely not understood. Sleep homeostasis is distinct from, but also linked to, the circadian clock. It is only in the last two decades that our understanding of some sleep disorders has been revealed. These breakthroughs were mostly fueled by intensive investigation using genetic tools. Although modern human genetics has revolutionized scientific research of neurologic disorders beginning ~35 years ago, studies of sleep and sleep disorders have lagged behind those of many neurologic diseases. This is due to the complexity in phenotyping behaviors like sleep and the fact that sleep is strongly influenced by environmental and other factors. We have long been aware that the amount of sleep required by individuals is normally distributed in the general population with small proportions of people being natural short or natural long sleepers. However, it has been less than a decade since Mendelian families of natural short sleepers have been recognized. Recent work has made significant advances and mechanistic insights of several sleep disorders as well as familial natural short sleepers by using ever-improving human genetic and cellular molecular tools. Given recent advances into genetic and biologic understanding of sleep, the hope of understanding this indispensable process is closer. Ultimately, our growing understanding will lead to more effective treatments of human sleep disorders.

Selection for long and short sleep duration in Drosophila melanogaster reveals the complex genetic network underlying natural variation in sleep

Why do some individuals need more sleep than others? Forward mutagenesis screens in flies using engineered mutations have established a clear genetic component to sleep duration, revealing mutants that convey very long or short sleep. Whether such extreme long or short sleep could exist in natural populations was unknown. We applied artificial selection for high and low night sleep duration to an outbred population of Drosophila melanogaster for 13 generations. At the end of the selection procedure, night sleep duration diverged by 9.97 hours in the long and short sleeper populations, and 24-hour sleep was reduced to 3.3 hours in the short sleepers. Neither long nor short sleeper lifespan differed appreciably from controls, suggesting little physiological consequences to being an extreme long or short sleeper. Whole genome sequence data from seven generations of selection revealed several hundred thousand changes in allele frequencies at polymorphic loci across the genome. Combining the data from long and short sleeper populations across generations in a logistic regression implicated 126 polymorphisms in 80 candidate genes, and we confirmed three of these genes and a larger genomic region with mutant and chromosomal deficiency tests, respectively. Many of these genes could be connected in a single network based on previously known physical and genetic interactions. Candidate genes have known roles in several classic, highly conserved developmental and signaling pathways—EGFR, Wnt, Hippo, and MAPK. The involvement of highly pleiotropic pathway genes suggests that sleep duration in natural populations can be influenced by a wide variety of biological processes, which may be why the purpose of sleep has been so elusive.

One of the biggest mysteries in biology is the need to sleep. Sleep duration has an underlying genetic basis, suggesting that very long and short sleep times could be bred for experimentally. How far can sleep duration be driven up or down? Here we achieved extremely long and short night sleep duration by subjecting a wild-derived population of Drosophila melanogaster to an experimental breeding program. At the end of the breeding program, long sleepers averaged 9.97 hours more nightly sleep than short sleepers. We analyzed whole-genome sequences from seven generations of the experimental breeding to identify allele frequencies that diverged between long and short sleepers, and verified genes and genomic regions with mutation and deficiency testing. These alleles map to classic developmental and signaling pathways, implicating many diverse processes that potentially affect sleep duration.

Genetic Influences on Evening Preference Overlap with Those for Bipolar Disorder in a Sample of Mexican Americans and American Indians

Diurnal preference (e.g., being an owl or lark) has been associated with several psychiatric disorders including bipolar disorder (BP), major depressive disorder, and substance use disorders. Previous large-scale genome-wide association studies (GWAS) aimed at identifying genetic influences on diurnal preference have exclusively included subjects of European ancestry. This study examined the genetic architecture of diurnal preference in two minority samples: a young adult sample of Mexican Americans (MAs), and a family-based sample of American Indians (AIs). Typed or imputed variants from exome chip data from the MA sample and low pass whole-genome sequencing from the AI cohort were analyzed using a mixed linear model approach for association with being an owl, as defined by a usual bedtime after 23:00 hrs. Genetic risk score (GRS) profiling detected shared genetic risk between evening preference and related disorders. Four variants in KIAA1549 like (KIAA1549L), a gene previously associated with attempted suicide in bipolar patients, were suggestively associated with being an owl at p < 1.82E-05; post hoc analyses showed the top variant trending in both the MA and AI cohorts at p = 2.50E-05 and p = .030, respectively. Variants associated with BP at p < .03 from the Psychiatric Genomics Consortium nominally predicted being an owl in the MA/AI cohort at p = .012. This study provides some additional evidence that genetic risk factors for BP also confer risk for being an owl in MAs/AIs and that evening preference may be a useful endophenotype for future studies of BP.

Transcriptional Signatures of Sleep Duration Discordance in Monozygotic Twins

Introduction

Habitual short sleep duration is associated with adverse metabolic, cardiovascular, and inflammatory effects. Co-twin study methodologies account for familial (eg, genetics and shared environmental) confounding, allowing assessment of subtle environmental effects, such as the effect of habitual short sleep duration on gene expression. Therefore, we investigated gene expression in monozygotic twins discordant for actigraphically phenotyped habitual sleep duration.

Methods

Eleven healthy monozygotic twin pairs (82% female; mean age 42.7 years; SD = 18.1), selected based on subjective sleep duration discordance, were objectively phenotyped for habitual sleep duration with 2 weeks of wrist actigraphy. Peripheral blood leukocyte (PBL) RNA from fasting blood samples was obtained on the final day of actigraphic measurement and hybridized to Illumina humanHT-12 microarrays. Differential gene expression was determined between paired samples and mapped to functional categories using Gene Ontology. Finally, a more comprehensive gene set enrichment analysis was performed based on the entire PBL transcriptome.

Results

The mean 24-hour sleep duration of the total sample was 439.2 minutes (SD = 46.8 minutes; range 325.4-521.6 minutes). Mean within-pair sleep duration difference per 24 hours was 64.4 minutes (SD = 21.2; range 45.9-114.6 minutes). The twin cohort displayed distinctive pathway enrichment based on sleep duration differences. Habitual short sleep was associated with up-regulation of genes involved in transcription, ribosome, translation, and oxidative phosphorylation. Unexpectedly, genes down-regulated in short sleep twins were highly enriched in immuno-inflammatory pathways such as interleukin signaling and leukocyte activation, as well as developmental programs, coagulation cascade, and cell adhesion.

Conclusions

Objectively assessed habitual sleep duration in monozygotic twin pairs appears to be associated with distinct patterns of differential gene expression and pathway enrichment. By accounting for familial confounding and measuring real life sleep duration, our study shows the transcriptomic effects of habitual short sleep on dysregulated immune response and provides a potential link between sleep deprivation and adverse metabolic, cardiovascular, and inflammatory outcomes.

Heritability of siesta and night-time sleep as continuously assessed by a circadian-related integrated measure

Siesta is a relevant aspect of sleep due to its posited relationship with health or cognitive function. However, unlike night-time sleep, studies about daytime-sleep determinants and characteristics are scarce, and the genetic/environmental structure of siesta is still unknown. Our aim was to explore the relative contribution of genetic and environmental factors to variation in sleep-wake rhythm, measured by a continuous assessment of temperature-activity-position (TAP), which allows for diurnal sleep analysis. The sample comprised 53 pairs of female twins (28 MZ and 25 DZ), selected from the Murcia Twin Register. Mean age of participants was 52 (SD: 6.03). Zygosity was determined by DNA. We conducted separate univariate analyses to study the sources of variance of daytime and night-time sleep parameters. About 60% of the sample reported to take siesta at least once a week. Heritability of taking siesta and daytime sleep duration was 65 and 61% respectively. Other sleep parameters obtained by TAP showed heritability estimates between 36 and 69%, suggesting a relevant impact of genetic factors on sleep rhythm. This is the first study to investigate the relative contribution of genetic factors to siesta. By using TAP, we introduce a novel approach to the study of diurnal sleep characteristics.

Pleiotropic genetic effects influencing sleep and neurological disorders

Research evidence increasingly points to the large impact of sleep disturbances on public health. Many aspects of sleep are heritable and genes influencing traits such as timing, EEG characteristics, sleep duration, and response to sleep loss have been identified. Notably, large-scale genome-wide analyses have implicated numerous genes with small effects on sleep timing. Additionally, there has been considerable progress in the identification of genes influencing risk for some neurological sleep disorders. For restless legs syndrome, implicated variants are typically in genes associated with neuronal development. By contrast, genes conferring risk for narcolepsy function in the immune system. Many genetic variants associated with sleep disorders are also implicated in neurological disorders in which sleep abnormalities are common; for example, variation in genes involved in synaptic homoeostasis are implicated in autism spectrum disorder and sleep-wake control. Further investigation into pleiotropic roles of genes influencing both sleep and neurological disorders could lead to new treatment strategies for a variety of sleep disturbances.

Genetic Markers of Sleep and Sleepiness

The circadian clock interacts with the sleep homeostatic drive in humans. Chronotype and sleep parameters show substantial heritability, underscoring a genetic component to these measures. This article reviews the genetic underpinnings of chronotype and of sleep, including sleepiness, sleep quality and latency, and sleep timing and duration in healthy adult sleepers, drawing on candidate gene and genome-wide association studies. Notably, both circadian and noncircadian genes associate with individual differences in chronotype and in sleep parameters. The article concludes with a brief discussion of future research directions.