Family studies in insomnia

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.

Adaptation and Validation of the Turkish Version of the Ford Insomnia Response to Stress Test in University Students

Objective

We adapted the Ford Insomnia Response to Stress Test to Turkish (FIRST-T) and validated it.

Methods

We randomly divided 774 Turkish university students into two equal groups for exploratory (EFA) and confirmatory factor analysis (CFA). McDonald's omega and Cronbach's alpha values were utilized for reliability analyses. Item response theory (IRT) approach also used for psychometric properties on the full sample. For discriminant validity, study sample were classified into high and low sleep reactivity groups, and their sociodemographic and sleep data were compared.

Results

EFA results suggested a one-factor structure of the FIRST-T, which was confirmed by CFA results. The FIRST-T had solid internal reliability. Item analysis results showed that all the items could distinguish between low and high scorers. This scale showed the same construct (clinical insomnia vs good sleepers) across the sexes in multi-group CFA and differential item functioning results. In the high FIRST-T score group, sleep quality, severity of insomnia, and anxiety scores were higher. In this group, more participants had clinical insomnia according to the Insomnia Severity Index (ISI) and were poor sleepers according to the Pittsburg Sleep Quality Index (PSQI) (p < 0.01).

Conclusion

The FIRST-T has robust psychometric properties that assesses sleep reactivity among university students.

Evaluating the Effects of Diet-Gut Microbiota Interactions on Sleep Traits Using the UK Biobank Cohort

Previous studies showed that diet and gut microbiota had a correlation with sleep. However, the potential interaction effects of diet and gut microbiota on sleep are still unclear. The phenotypic data of insomnia (including 374,505 subjects) and sleep duration (including 372,805 subjects) were obtained from the UK Biobank cohort. The Single Nucleotide Polymorphisms (SNPs) associated with 114 gut microbiota, 84 dietary habits, and 4 dietary compositions were derived from the published Genome-wide Association Study (GWAS). We used Linkage Disequilibrium Score Regression (LDSC) to estimate the genetic correlation and colocalization analysis to assess whether dietary habits and insomnia/sleep duration shared a causal variant in a region of the genome. Using UK Biobank genotype data, the polygenetic risk score of gut microbiota, dietary habits, and dietary compositions were calculated for each subject. Logistic regression and linear regression models were used to assess the potential effects of diet-gut microbiota interactions on sleep phenotypes, including insomnia and sleep duration. Insomnia and sleep duration were used as dependent variables, and sex, age, the Townsend Deprivation Index scores, and smoking and drinking habits were selected as covariates in the regression analysis. All statistical analyses were conducted using R-3.5.1 software. Significant genetic correlations were discovered between insomnia/sleep duration and dietary habits. Further, we found several significant dietary compositions-gut microbiota interactions associated with sleep, such as fat × G_Collinsella_RNT (p = 1.843 × 10-2) and protein × G_Collinsella_HB (p = 7.11 × 10-3). Besides, multiple dietary habits-gut microbiota interactions were identified for sleep, such as overall beef intake × G_Desulfovibrio_RNT (p = 3.26 × 10-4), cups of coffee per day × G_Escherichia_Shigella_RNT (p = 1.14 × 10-3), and pieces of dried fruit per day × G_Bifidobacterium_RNT (p = 5.80 × 10-3). This study reported multiple diet-gut microbiota interactions associated with sleep, which may provide insights into the biological mechanisms of diet and gut microbiota affecting sleep.

Family aggregation of sleep characteristics: Results of the Heinz Nixdorf Recall and the Multi-Generation Study

INTRODUCTION

Poor sleep is a risk factor for adverse health events. For health prevention, it may be helpful to know whether poor sleep or sleep disorders in individuals are associated with sleep problems in their partners or children.

METHODS

In the MultiGeneration Study (MGS, conducted from 2013 to 2016), 1237 partners (aged 27 to 90 years) and 1660 adult children (aged 18 to 66 years) of index persons were recruited. Index persons are participants of the Heinz Nixdorf Recall Study, a population-based cohort study in the Ruhr area (study start 1999-2001, 4841 participants aged 45-75 years). We used two analysis populations: one with 1181 index persons whose partners were in MGS, and one with 1083 index persons with at least one adult child in MGS. Sleep characteristics were assessed using questionnaires (including the Pittsburgh Sleep Quality Index). The exposure was the presence of a sleep characteristic of the index subject.

RESULTS

Children showed the investigated sleep characteristics more often if these were also present in their parent (e.g., RR (relative risk) = 1.28 (95% CI: 1.06-1.55) for poor sleep quality). In partners, strong associations were observed for rising times and napping, but only weak associations for snoring, poor sleep quality and sleep disorders. Snoring of the bed partner is a risk factor for poor sleep (e.g., RR = 1.67 (0.91-3.07) for difficulties falling asleep).

CONCLUSION

Aggregation is observed for many sleep characteristics in people living in partnerships as well as in parents and their adult children.

Integrative genomics analysis identifies five promising genes implicated in insomnia risk based on multiple omics datasets

In recent decades, many genome-wide association studies on insomnia have reported numerous genes harboring multiple risk variants. Nevertheless, the molecular functions of these risk variants conveying risk to insomnia are still ill-studied. In the present study, we integrated GWAS summary statistics (N=386,533) with two independent brain expression quantitative trait loci (eQTL) datasets (N=329) to determine whether expression-associated SNPs convey risk to insomnia. Furthermore, we applied numerous bioinformatics analyses to highlight promising genes associated with insomnia risk. By using Sherlock integrative analysis, we detected 449 significant insomnia-associated genes in the discovery stage. These identified genes were significantly overrepresented in six biological pathways including Huntington’s disease (P=5.58 × 10⁻⁵), Alzheimer’s disease (P=5.58 × 10⁻⁵), Parkinson’s disease (P=6.34 × 10⁻⁵), spliceosome (P=1.17 × 10⁻⁴), oxidative phosphorylation (P=1.09 × 10⁻⁴), and wnt signaling pathways (P=2.07 × 10⁻⁴). Further, five of these identified genes were replicated in an independent brain eQTL dataset. Through a PPI network analysis, we found that there existed highly functional interactions among these five identified genes. Three genes of LDHA (P=0.044), DALRD3 (P=5.0 × 10⁻⁵), and HEBP2 (P=0.032) showed significantly lower expression level in brain tissues of insomnic patients than that in controls. In addition, the expression levels of these five genes showed prominently dynamic changes across different time points between behavioral states of sleep and sleep deprivation in mice brain cortex. Together, the evidence of the present study strongly suggested that these five identified genes may represent candidate genes and contributed risk to the etiology of insomnia.

A Prevention Program for Insomnia in At-risk Adolescents: A Randomized Controlled Study

OBJECTIVES

To prevent the future development of insomnia in at-risk adolescents.

METHODS

A randomized controlled trial comparing 4 weekly insomnia prevention program with a nonactive control group. Subjects were assessed at baseline, postintervention, and 6 and 12 months after intervention. Assessors were blinded to the randomization. Analyses were conducted on the basis of the intention-to-treat principles.

RESULTS

A total of 242 adolescents with family history of insomnia and subthreshold insomnia symptoms were randomly assigned to an intervention group (n = 121; mean age = 14.7 ± 1.8; female: 51.2%) or control group (n = 121; mean age = 15.0 ± 1.7; female: 62.0%). There was a lower incidence rate of insomnia disorder (both acute and chronic) in the intervention group compared with the control group (5.8% vs 20.7%; P = .002; number needed to treat = 6.7; hazard ratio = 0.29; 95% confidence interval: 0.12-0.66; P = .003) over the 12-month follow-up. The intervention group had decreased insomnia symptoms (P = .03) and reduced vulnerability to stress-related insomnia (P = .03) at postintervention and throughout the 12-month follow-up. Decreased daytime sleepiness (P = .04), better sleep hygiene practices (P = .02), and increased total sleep time (P = .05) were observed at postintervention. The intervention group also reported fewer depressive symptoms at 12-month follow-up (P = .02) compared with the control group.

CONCLUSIONS

A brief cognitive behavioral program is effective in preventing the onset of insomnia and improving the vulnerability factors and functioning outcomes.

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.

Association between 5-hydroxytryptamine gene polymorphism rs140700 and primary insomnia in Chinese population

BACKGROUND

Primary insomnia is a worldwide problem and it has a considerable negative impact on one's physical and mental health. Studies have shown that non-synonymous Single-nucleotide polymorphisms in 5-hydroxytryptamine (serotonin or 5-HT) are related to primary insomnia. Previous studies have shown that 5-HT polymorphism (rs140700) is related to depression, and insomnia is often accompanied by depression and anxiety. The relationship between this site and primary insomnia is unknown. We speculated that this site may be related to primary insomnia, so we investigated the relationship between rs140700 and primary insomnia.

AIMS

To explore the relationship between the 5-HT gene polymorphism rs140700 and primary insomnia.

METHODS

In this study, we included 57 patients with primary insomnia and 54 age- and gender-matched normal controls. The subjects who belonged to the Chinese population were subjected to polysomnography for three consecutive nights. Their sleep quality was assessed, and the genotypes of the 5-hydroxytryptamine (5-HT) gene polymorphism rs140700 were determined by the flight mass spectrometry.

RESULTS

The genotype distributions of the 5-HT gene polymorphism rs140700 were in Hardy-Weinberg equilibrium in both patients and controls (P > 0.05). The allele and genotype distributions of this variant were comparable between the patients and controls in all subjects and between genders (all P > 0.05). The influence of rs140700 on percentage of stage 1 (P = 0.015) change and arousal index (P = 0.028) of primary insomnia was statistically significant. The logistic multi-factor regression analysis results revealed that 5-HT gene polymorphism rs140700 was not a risk factor for primary insomnia in the Chinese population (P = 0.589).

CONCLUSIONS

The 5-HT gene polymorphism rs140700 may not be a susceptibility locus for primary insomnia in the Chinese population.

The involvement of sleep in the relationship between the serotonin transporter gene-linked polymorphic region (5-HTTLPR) and depression: A systematic review

BACKGROUND

Recent meta-analyses stimulate an ongoing debate whether 5-HTTLPR modulates the risk for depression including a more pronounced association between stress and depression in the short (S) allele relative to the long (L) allele. Elucidating the pathways by which 5-HTTLPR contributes to depression could resolve this controversy. Insomnia independently contributes to the onset and course of negative affective symptoms and, hence, represents one of the primary risk factors for depression. To evaluate the relevance of this relationship for the interaction between 5-HTTLPR and stress in depression, the present review investigated the moderating influence of 5-HTTLPR on the relationship between stress and sleep quality as well as on the relationship between sleep and affective symptomatology.

METHODS

A systematic search was performed in the PubMed and PsycINFO databases to include a complete outline of studies investigating the relationships of interest.

RESULTS

Results of the included articles reveal that the 5-HTTLPR S-allele relative to the L-allele increases the risk for stress-related sleep quality reductions and promotes the negative affective consequences of inadequate sleep.

LIMITATIONS

The apparent involvement of sleep in the association between 5-HTTLPR and depression remains to be more directly (empirically) examined and studies exploring the influence of 5-HTTLPR on sleep quality produced inconsistent results.

CONCLUSIONS

The reviewed findings support the involvement of sleep in the interaction between 5-HTTLPR and stress in depression. This could have important implications for the inconsistent findings characterizing this field of research and may provide valuable insight into the pathophysiological mechanisms underlying genetic contributions to depression.

The serotonin transporter gene-linked polymorphic region (5-HTTLPR) and the sleep-promoting effects of tryptophan: A randomized placebo-controlled crossover study

BACKGROUND

The low-expressive short (S) allele of a functional polymorphism (5-HTTLPR) within the serotonin (5-hydroxytriptamine; 5-HT) transporter gene (SLC6A4) has been associated with a reduced functioning of the brain 5-HT system relative to the long (L) allele. As a consequence, the S-allele is found to predispose individuals to a higher risk of sleep quality reduction and clinical insomnia.

AIMS

The present study investigated whether subchronic pre-sleep tryptophan administration could compensate for this predisposition by improving sleep in 5-HTTLPR S-allele carriers.

METHODS

In a double-blind placebo-controlled crossover design a sample of homozygous 5-HTTLPR S-allele (n = 47) and L-allele (n = 51) carriers were assessed for subjective (sleep diary) and objective (actigraphy) sleep during a treatment protocol consisting of 1 week of placebo (1000 mg/day) and 1 week of tryptophan administration (1000 mg/day).

RESULTS

The results support the sleep-promoting effects of tryptophan. Tryptophan improved objective sleep efficiency and objective wake after sleep onset irrespective of allelic variation. There was a marginally significant improvement of subjective sleep quality in the 5-HTTLPR S-allele group but not in the L-allele group following tryptophan relative to placebo intake. In contrast, a significantly poorer sleep quality in the S-allele as opposed to the L-allele group in the placebo condition was not observed in the tryptophan condition.

CONCLUSIONS

Tryptophan augmentation promises to be a valuable treatment strategy for sleep impairments related to genetic deficiencies in 5-HT functioning.

The impact of stress on sleep: Pathogenic sleep reactivity as a vulnerability to insomnia and circadian disorders

Sleep reactivity is the trait-like degree to which stress exposure disrupts sleep, resulting in difficulty falling and staying asleep. Individuals with highly reactive sleep systems experience drastic deterioration of sleep when stressed, whereas those with low sleep reactivity proceed largely unperturbed during stress. Research shows that genetics, familial history of insomnia, female gender and environmental stress influence how the sleep system responds to stress. Further work has identified neurobiological underpinnings for sleep reactivity involving disrupted cortical networks and dysregulation in the autonomic nervous system and hypothalamic-pituitary-adrenal axis. Sleep reactivity is most pathologically and clinically pertinent when in excess, such that high sleep reactivity predicts risk for future insomnia disorder, with early evidence suggesting high sleep reactivity corresponds to severe insomnia phenotypes (sleep onset insomnia and short sleep insomnia). High sleep reactivity is also linked to risk of shift-work disorder, depression and anxiety. Importantly, stress-related worry and rumination may exploit sensitive sleep systems, thereby augmenting the pathogenicity of sleep reactivity. With the development of cost-effective assessment of sleep reactivity, we can now identify individuals at risk of future insomnia, shift-work disorder and mental illness, thus identifying a target population for preventive intervention. Given that insomniacs with high sleep reactivity tend to present with severe insomnia phenotypes, patient sleep reactivity may inform triaging to different levels of treatment. Future research on sleep reactivity is needed to clarify its neurobiology, characterize its long-term prospective associations with insomnia and shift-work disorder phenotypes, and establish its prognostic value for mental illness and other non-sleep disorders.

Hyperarousal and sleep reactivity in insomnia: current insights

Hyperarousal is a key component in all modern etiological models of insomnia disorder. Overall patterns in the literature suggest that over-active neurobiological and psychological systems contribute to difficulty sleeping. Even so, mixed results regarding the specific mechanisms linking hyperarousal to sleep disturbance limit current etiological conceptualizations. Similar basal arousal profiles between individuals with high vs low risk for insomnia in the absence of stress exposure suggest that dysregulated stress "response" rather than general hyperarousal may be a more pertinent marker of risk. In this report, we discuss evidence for hyperarousal in insomnia and explore the role of sleep reactivity. A trait characteristic, sleep reactivity is the degree to which stress disrupts sleep, manifesting as difficulty falling and staying asleep. Premorbid sleep reactivity has been shown to identify individuals at risk for future insomnia disorder, such as highly reactive sleepers (whose sleep systems are sensitive to stress) who are at elevated disease risk. Research points to genetics, family history of insomnia, gender, and environmental stress as factors that influence sleep reactivity. Importantly, stress-related cognitive-emotional reactivity (e.g., rumination, worry) may exploit the vulnerability of a highly reactive sleep system. We propose that sleep reactivity and cognitive-emotional reactivity may share a bidirectional relationship, conferring an insalubrious environment for sleep in response to stress. Future research on sleep reactivity is needed to identify its neurobiology, characterize its relationship with cognitive-emotional reactivity, and explore the potential clinical utility of sleep reactivity in treatment planning.

Genome-wide association analysis of insomnia complaints identifies risk genes and genetic overlap with psychiatric and metabolic traits

Persistent insomnia is among the most frequent complaints in general practice. To identify genetic factors for insomnia complaints, we performed a genome-wide association study (GWAS) and a genome-wide gene-based association study (GWGAS) in 113,006 individuals. We identify three loci and seven genes associated with insomnia complaints, with the associations for one locus and five genes supported by joint analysis with an independent sample (n = 7,565). Our top association (MEIS1, P < 5 × 10-8) has previously been implicated in restless legs syndrome (RLS). Additional analyses favor the hypothesis that MEIS1 exhibits pleiotropy for insomnia and RLS and show that the observed association with insomnia complaints cannot be explained only by the presence of an RLS subgroup within the cases. Sex-specific analyses suggest that there are different genetic architectures between the sexes in addition to shared genetic factors. We show substantial positive genetic correlation of insomnia complaints with internalizing personality traits and metabolic traits and negative correlation with subjective well-being and educational attainment. These findings provide new insight into the genetic architecture of insomnia.

Genetic Pathways to Insomnia

This review summarizes current research on the genetics of insomnia, as genetic contributions are thought to be important for insomnia etiology. We begin by providing an overview of genetic methods (both quantitative and measured gene), followed by a discussion of the insomnia genetics literature with regard to each of the following common methodologies: twin and family studies, candidate gene studies, and genome-wide association studies (GWAS). Next, we summarize the most recent gene identification efforts (primarily GWAS results) and propose several potential mechanisms through which identified genes may contribute to the disorder. Finally, we discuss new genetic approaches and how these may prove useful for insomnia, proposing an agenda for future insomnia genetics research.

Overview of Common Sleep Disorders and Intersection with Dermatologic Conditions

Sleep disorders are very common, often under-recognized and therefore undertreated, are associated with a myriad of medical conditions and could lead to significant impairment of quality of life. This review provides an up-to-date synopsis of common sleep disorders encompassing insufficient sleep syndrome, insomnia, circadian rhythm disorders and obstructive sleep apnea with a brief overview of epidemiology, screening, diagnostic testing and treatment. We also emphasize the emerging area of the intersection of sleep disorders and dermatologic conditions and present compelling data regarding underlying mechanisms including sleep dysfunction in relation to disorders of skin inflammation, aging and skin cancer.

Sleep system sensitization: evidence for changing roles of etiological factors in insomnia

OBJECTIVES

To test for sensitization of the sleep system in response to insomnia development and major life stress. In addition, to evaluate the impact on depression and anxiety associated with sleep system sensitization.

METHODS

A longitudinal study with three annual assessments. The community-based sample included 262 adults with no history of insomnia or depression who developed insomnia one year after baseline (67.6% female; 44.0 ± 13.4 yr). Measures included the Ford Insomnia Response to Stress Test to assess sleep reactivity, Quick Inventory of Depressive Symptomatology, and Beck Anxiety Inventory. Insomnia classification was based on DSM-IV criteria. Sleep system sensitization was operationally defined as significant increases in sleep reactivity.

RESULTS

Sensitization of the sleep system was observed from baseline to insomnia onset at 1-yr follow-up among insomniacs with low premorbid vulnerability (p < 0.001), resulting in 68.3% of these individuals re-classified as highly sleep reactive. Major life stress was associated with greater sleep system sensitization (p = 0.02). Results showed that sleep reactivity at 2-yr follow-up remained elevated among those with low premorbid vulnerability, even after insomnia remission (p < 0.01). Finally, analyses revealed that increases in sleep reactivity predicted greater depression (p < 0.001) and anxiety (p < 0.001) at insomnia onset. The impact of sensitization on depression was stable at 2-yr follow-up (p = 0.01).

CONCLUSIONS

Evidence supports sensitization of the sleep system as a consequence of insomnia development and major life stress among individuals with low premorbid sleep reactivity. Sleep system sensitization may serve as a mechanism by which insomnia is perpetuated. Harmful effects of the sensitization process may increase risk for insomnia-related depression and anxiety.

Identifying At-Risk Individuals for Insomnia Using the Ford Insomnia Response to Stress Test

STUDY OBJECTIVES

A primary focus of the National Institute of Mental Health's current strategic plan is "predicting" who is at risk for disease. As such, the current investigation examined the utility of premorbid sleep reactivity in identifying a specific and manageable population at elevated risk for future insomnia.

METHODS

A community-based sample of adults (n = 2,892; 59.3% female; 47.9 ± 13.3 y old) with no lifetime history of insomnia or depression completed web-based surveys across three annual assessments. Participants reported parental history of insomnia, demographic characteristics, sleep reactivity on the Ford Insomnia in Response to Stress Test (FIRST), and insomnia symptoms. DSM-IV diagnostic criteria were used to determine insomnia classification.

RESULTS

Baseline FIRST scores were used to predict incident insomnia at 1-y follow-up. Two clinically meaningful FIRST cutoff values were identified: FIRST ≥ 16 (sensitivity 77%; specificity 50%; odds ratio [OR] = 2.88, P < 0.001); and FIRST ≥ 18 (sensitivity 62%; specificity 67%; OR = 3.32, P < 0.001). Notably, both FIRST cut-points outperformed known maternal (OR = 1.49-1.59, P < 0.01) and paternal history (P = NS) in predicting insomnia onset, even after controlling for stress exposure and demographic characteristics. Of the incident cases, insomniacs with highly reactive sleep systems reported longer sleep onset latencies (FIRST ≥ 16: 65 min; FIRST ≥ 18: 68 min) than participants with nonreactive insomnia (FIRST < 16: 37 min; FIRST < 18: 44 min); these groups did not differ on any other sleep parameters.

CONCLUSIONS

The current study established a cost- and time-effective strategy for identifying individuals at elevated risk for insomnia based on trait sleep reactivity. The FIRST accurately identifies a focused target population in which the psychobiological processes complicit in insomnia onset and progression can be better investigated, thus improving future preventive efforts.

Insomnia disorder

Insomnia disorder affects a large proportion of the population on a situational, recurrent or chronic basis and is among the most common complaints in medical practice. The disorder is predominantly characterized by dissatisfaction with sleep duration or quality and difficulties initiating or maintaining sleep, along with substantial distress and impairments of daytime functioning. It can present as the chief complaint or, more often, co-occurs with other medical or psychiatric disorders, such as pain and depression. Persistent insomnia has been linked with adverse long-term health outcomes, including diminished quality of life and physical and psychological morbidity. Despite its high prevalence and burden, the aetiology and pathophysiology of insomnia is poorly understood. In the past decade, important changes in classification and diagnostic paradigms have instigated a move from a purely symptom-based conceptualization to the recognition of insomnia as a disorder in its own right. These changes have been paralleled by key advances in therapy, with generic pharmacological and psychological interventions being increasingly replaced by approaches that have sleep-specific and insomnia-specific therapeutic targets. Psychological and pharmacological therapies effectively reduce the time it takes to fall asleep and the time spent awake after sleep onset, and produce a modest increase in total sleep time; these are outcomes that correlate with improvements in daytime functioning. Despite this progress, several challenges remain, including the need to improve our knowledge of the mechanisms that underlie insomnia and to develop more cost-effective, efficient and accessible therapies.

Genetic variation in melatonin pathway enzymes in children with autism spectrum disorder and comorbid sleep onset delay

Sleep disruption is common in individuals with autism spectrum disorder (ASD). Genes whose products regulate endogenous melatonin modify sleep patterns and have been implicated in ASD. Genetic factors likely contribute to comorbid expression of sleep disorders in ASD. We studied a clinically unique ASD subgroup, consisting solely of children with comorbid expression of sleep onset delay. We evaluated variation in two melatonin pathway genes, acetylserotonin O-methyltransferase (ASMT) and cytochrome P450 1A2 (CYP1A2). We observed higher frequencies than currently reported (p < 0.04) for variants evidenced to decrease ASMT expression and related to decreased CYP1A2 enzyme activity (p ≤ 0.0007). We detected a relationship between genotypes in ASMT and CYP1A2 (r(2) = 0.63). Our results indicate that expression of sleep onset delay relates to melatonin pathway genes.

Pedunculopontine arousal system physiology - Implications for insomnia

We consider insomnia a disorder of waking rather than a disorder of sleep. This review examines the role of the reticular activating system, especially the pedunculopontine nucleus, in the symptoms of insomnia, mainly representing an overactive waking drive. We determined that high frequency activity during waking and REM sleep is controlled by two different intracellular pathways and channel types in PPN cells. We found three different PPN cell types that have one or both channels and may be active during waking only, REM sleep only, or both. These discoveries point to a specific mechanism and novel therapeutic avenues for insomnia.

Cognitive-emotional hyperarousal in the offspring of parents vulnerable to insomnia: a nuclear family study

Cognitive-emotional hyperarousal is believed to be a predisposing factor for insomnia; however, there is limited information on the association of familial vulnerability to insomnia and cognitive-emotional hyperarousal. The aim of this study was to estimate the heritability of stress-related insomnia and examine whether parental vulnerability to stress-related insomnia is associated with cognitive-emotional hyperarousal in their offspring. We studied a volunteer sample of 135 nuclear families comprised of 270 middle-aged (51.5 ± 5.4 years) fathers and mothers and one of their biological offspring (n = 135, 20.2 ± 1.1 years). We measured vulnerability to stress-related insomnia (i.e. Ford Insomnia Response to Stress Test: FIRST), perceived stress, depression and anxiety in all participants, and arousability, presleep cognitive and somatic arousal, coping and personality in the offspring. We found a heritability estimate of 29% for FIRST scores. High FIRST parents had three to seven times the odds of having offspring highly vulnerable to stress-related insomnia. Offspring of high FIRST parents showed higher arousability, presleep cognitive arousal and emotion-oriented coping. Furthermore, high FIRST mothers contributed to offspring's higher anxiety and lower task-oriented coping, while high FIRST fathers contributed to offspring's higher presleep somatic arousal and conscientiousness. Vulnerability to stress-related insomnia is significantly heritable. Parents vulnerable to stress-related insomnia have offspring with cognitive-emotional hyperarousal who rely upon emotion-oriented coping. These data give support to the notion that arousability and maladaptive coping are key factors in the aetiology of insomnia.

Who is predisposed to insomnia: a review of familial aggregation, stress-reactivity, personality and coping style

Insomnia is a common health complaint world-wide. Insomnia is a risk factor in the development of other psychological and physiological disorders. Therefore understanding the mechanisms which predispose an individual to developing insomnia has great transdiagnostic value. However, whilst it is largely accepted that a vulnerable phenotype exists there is a lack of research which aims to systematically assess the make-up of this phenotype. This review outlines the research to-date, considering familial aggregation and the genetics and psychology of stress-reactivity. A model will be presented in which negative affect (neuroticism) and genetics (5HTTLPR) are argued to lead to disrupted sleep via an increase in stress-reactivity, and further that the interaction of these variables leads to an increase in learned negative associations, which further increase the likelihood of poor sleep and the development of insomnia.

A genome-wide association study of sleep habits and insomnia

Several aspects of sleep behavior such as timing, duration and quality have been demonstrated to be heritable. To identify common variants that influence sleep traits in the population, we conducted a genome-wide association study of six sleep phenotypes assessed by questionnaire in a sample of 2,323 individuals from the Australian Twin Registry. Genotyping was performed on the Illumina 317, 370, and 610K arrays and the SNPs in common between platforms were used to impute non-genotyped SNPs. We tested for association with more than 2,000,000 common polymorphisms across the genome. While no SNPs reached the genome-wide significance threshold, we identified a number of associations in plausible candidate genes. Most notably, a group of SNPs in the third intron of the CACNA1C gene ranked as most significant in the analysis of sleep latency (P = 1.3 × 10⁻⁶). We attempted to replicate this association in an independent sample from the Chronogen Consortium (n = 2,034), but found no evidence of association (P = 0.73). We have identified several other suggestive associations that await replication in an independent sample. We did not replicate the results from previous genome-wide analyses of self-reported sleep phenotypes after correction for multiple testing.

Familial aggregation and heritability of insomnia in a community-based study

BACKGROUND

Emerging data suggested a significant familial aggregation of insomnia. We aimed to clarify the familial aggregation and heritability of insomnia disorder by using structural clinical interviews for the ascertainment of insomnia and psychiatric disorders in a community-based sample.

METHODS

Seventy-five adolescents with insomnia and their 180 first degree relatives, together with 141 age- and sex-matched non-insomnia controls and their 382 first degree relatives, were recruited. Each subject underwent a structured clinical interview and completed a series of psychometric inventories. The rates of insomnia disorder among the first degree relatives were employed to analyze familial aggregation. Heritability of insomnia was analyzed by SOLAR program as based on father-mother-offspring trios.

RESULTS

Our study confirmed a significant familial aggregation of insomnia with a first degree relatives' recurrence risk of 2.33 for current insomnia and 2.82 for lifetime insomnia, respectively. The heritability±SE of current and lifetime insomnia disorder was 0.48±0.13 and 0.61±0.11 (p<0.001), respectively, which were higher than insomnia symptoms as estimated by the Insomnia Severity Inventory (h(2)±SE=0.27±0.09) and the Pittsburgh Sleep Quality Index (h(2)±SE=0.30±0.11). After exclusion of comorbid psychiatric disorders, the heritability for current and lifetime primary insomnia was 0.45±0.17 (p=0.007) and 0.58±0.21 (p=0.004), respectively.

CONCLUSIONS

Our study demonstrates a significant familial aggregation with a high heritability of insomnia disorder. The strong heritability of insomnia persists despite the exclusion of psychiatric disorders. Further molecular genetic investigation of insomnia is indicated.

Sleep Characteristics, Sleep Problems, and Associations to Quality of Life among Psychotherapists

Sleep problems, especially insomnia, are a common complaint among adults. International studies have shown prevalence rates between 4.7 and 36.2% for sleep difficulties in general, whereas 13.1–28.1% report insomnia symptoms. Sleep problems are associated with lower social and academic performance and can have a severe impact on psychological and physical health. Psychotherapists are suppliers within the public health system. The goal of this study was to outline sleep characteristics, prevalence of sleep problems, insomnia, and associations of quality of life among psychotherapists. A total of 774 psychotherapists (74.7% women; mean age 46 years) participated in the study. Sleep characteristics, sleep problems, well-being, life satisfaction and workload, as well as specific job demands, were assessed via a questionnaire. Analyses revealed that more than 4.2% of the surveyed psychotherapists have difficulties falling asleep, 12.7% often wake up in the night, and 26.6% feel tired, and 3.4% think that their interrupted sleep affects work performance. About 44.1% of them suffer from symptoms of insomnia. Path models showed that insomnia is significantly related to well-being and life satisfaction.

[Frequently occurring sleep disorders]

Some sleep disorders are frequently found in the general population. The most common include restless legs syndrome, insomnia, and sleep apnea. These sleep disorders are well classified and can easily be diagnosed and treated. Since they are risk factors for cardiovascular and psychiatric disorders, early diagnosis and treatment are essential to prevent these sequelae. The impairments caused by these sleep disorders (e.g., due to daytime sleepiness, sleep disruption, or cognitive deficits) can result in a significant reduction in a person's quality of life. The diagnostic and therapeutic recommendations were taken from the S3 guideline "Nonrestorative sleep/sleep disorders" by the German Sleep Society. The levels of evidence were given according to the recommendations of the Oxford Centre for Evidence-based Medicine.

Sleep reactivity and insomnia: genetic and environmental influences

STUDY OBJECTIVES

Determine the genetic and environmental contributions to sleep reactivity and insomnia.

DESIGN

Population-based twin cohort.

PARTICIPANTS

1782 individual twins (988 monozygotic or MZ; 1,086 dizygotic or DZ), including 744 complete twin pairs (377 MZ and 367 DZ). Mean age was 22.5 ± 2.8 years; gender distribution was 59% women.

MEASUREMENTS

Sleep reactivity was measured using the Ford Insomnia Response to Stress Test (FIRST). The criterion for insomnia was having difficulty falling asleep, staying asleep, or nonrefreshing sleep "usually or always" for ≥ 1 month, with at least "somewhat" interference with daily functioning.

RESULTS

The prevalence of insomnia was 21%. Heritability estimates for sleep reactivity were 29% for females and 43% for males. The environmental variance for sleep reactivity was greater for females and entirely due to nonshared effects. Insomnia was 43% to 55% heritable for males and females, respectively; the sex difference was not significant. The genetic variances in insomnia and FIRST scores were correlated (r = 0.54 in females, r = 0.64 in males), as were the environmental variances (r = 0.32 in females, r = 0.37 in males). In terms of individual insomnia symptoms, difficulty staying asleep (25% to 35%) and nonrefreshing sleep (34% to 35%) showed relatively more genetic influences than difficulty falling asleep (0%).

CONCLUSIONS

Sleep reactivity to stress has a substantial genetic component, as well as an environmental component. The finding that FIRST scores and insomnia symptoms share genetic influences is consistent with the hypothesis that sleep reactivity may be a genetic vulnerability for developing insomnia.

Heritability and mortality risk of insomnia-related symptoms: a genetic epidemiologic study in a population-based twin cohort

STUDY OBJECTIVES

Our aim was to estimate heritability in phenotypic insomnia and the association between insomnia and mortality.

DESIGN

Representative follow-up study.

PARTICIPANTS

1990 survey of the Finnish Twin Cohort (N = 12502 adults; 1554 monozygotic and 2991 dizygotic twin pairs).

MEASUREMENTS

Current insomnia-related symptoms (insomnia in general, difficulty in initiating sleep, sleep latency, nocturnal awakening, early morning awakening, and non-restorative sleep assessed in the morning and during the day) were asked. Latent class analysis was used to classify subjects into different sleep quality classes. Quantitative genetic modelling was used to estimate heritability. Mortality data was obtained from national registers until end of April 2009.

RESULTS

The heritability estimates of each symptom were similar in both genders varying from 34% (early morning awakening) to 45% (nocturnal awakening). The most parsimonious latent class analysis produced 3 classes: good sleepers (48%), average sleepers (up to weekly symptoms, 40%), and poor sleepers (symptoms daily or almost daily, 12%). The heritability estimate for the cluster was 46% (95% confidence interval 41% to 50%). In a model adjusted for smoking, BMI, and depressive symptoms, the all-cause mortality of poor sleepers was elevated (excess mortality 55% in men and 51% in women). Further adjustment for sleep length, use of sleep promoting medications, and sleep apnea-related symptoms did not change the results.

CONCLUSIONS

Insomnia-related symptoms were common in both genders. The symptoms and their clusters showed moderate heritability estimates. A significant association was found between poor sleep and risk of mortality, especially in those with somatic disease.

Restricted sleep among adolescents: prevalence, incidence, persistence, and associated factors

The objective is to examine incidence, prevalence, and persistence of restricted or short sleep among adolescents and associated risk factors. Data are from a sample of 4,175 youths aged 11 to 17 at baseline and 3,134 followed up 1 year later. Restricted sleep was defined as 6 hr or less per night. Prevalence was 20%, 1-year incidence was 17%, and chronicity was 54%. Analyses identified few independent predictors: female, older age, schoolwork, extracurricular activities, and life stress. Odds ratios for incidence of sleep restriction on weeknights were 10 for 8 or more factors and 17 for persistence with 8 or more risk factors. This prospective study documents that incidence of sleep restriction was high. Restricted sleep also was prevalent and chronic and, like many other health problems, has multifactorial origins. Having multiple risk factors substantially increased risk of restricted sleep. Given the importance of sleep in this population, more focus is clearly needed, both clinically and epidemiologically.

Association between a serotonin transporter length polymorphism and primary insomnia

STUDY OBJECTIVE

To test the hypothesis that a 44-base-pair insertion/deletion polymorphism in the 5' regulatory region of the serotonin transporter gene (5-HTTLPR) is associated with primary insomnia.

DESIGN

Association study.

SETTING

Sleep laboratory at the Central Institute of Mental Health, Mannheim, Germany.

PATIENTS

157 patients with primary insomnia and 827 healthy controls.

INTERVENTIONS

N/A.

MEASUREMENT AND RESULTS

We found the short (s-) allele of the 5-HTTLPR to be significantly more frequent in patients suffering from insomnia than in control individuals (47.1% vs. 39.9%: OR = 1.34).

CONCLUSIONS

This finding contributes to the understanding of the pathophysiology of primary insomnia and suggests a biological basis between the prevalent comorbidity of primary insomnia and other psychiatric disorders.

Approaches to unravel the genetics of sleep

Sleep and circadian rhythms are complex and inter-connected physiological processes. Relative to the remarkable progress made in identifying the genetic basis of circadian rhythms and some specific sleep disorders, efforts to identify genetic variants associated with normal variation in sleep have progressed more slowly. Two key issues concerning the design of such studies must be addressed in order to facilitate further progress. The first concerns the sleep related traits to be targeted. The second issue is the choice of the gene-mapping method (linkage, candidate gene association or genome-wide association). This paper discusses these issues, reviews published studies of sleep phenotypes, and recommends cost-effective methods to advance knowledge of the genetic determinants of normal sleep patterns.

Incidence and risk factors of insomnia in a population-based sample

INTRODUCTION

Despite the high prevalence of insomnia, there is little information about its incidence and risk factors. This study estimated the incidence of insomnia and examined potential risk factors in a cohort of good sleepers followed over a one-year period.

METHODS

Participants were 464 good sleepers who completed 3 postal evaluations over a one-year period (i.e., baseline, 6 months, and 12 months). Questionnaires assessed sleep, psychological and personality variables, stressful life events and coping skills, and health-related quality of life. Participants were categorized into 3 subgroups: (a) good sleepers (i.e., participants who remained good sleepers at the 3 assessments), (b) insomnia symptoms incident cases (i.e., developed insomnia symptoms either at 6- or 12-month follow-up), and (c) insomnia syndrome incident cases (i.e., developed an insomnia syndrome either at 6- or 12- month follow-up).

RESULTS

One-year incidence rates were 30.7% for insomnia symptoms and 7.4% for insomnia syndrome. These rates decreased to 28.8% and 3.9% for those without prior lifetime episode of insomnia. Compared to good sleepers and insomnia symptoms incident cases, insomnia syndrome incident cases presented a premorbid psychological vulnerability to insomnia, characterized by higher depressive and anxiety symptoms, lower extraversion, higher arousability, and poorer self-rated mental health at baseline. They also presented a higher level of bodily pain and a poorer general health. Five variables were associated with a new onset of an insomnia syndrome: previous episode of insomnia, positive family history of insomnia, higher arousability predisposition, poorer self-rated general health, and higher bodily pain.

CONCLUSION

The one-year insomnia incidence rate was very high and several psychological and health factors were associated with new onset insomnia. Improved knowledge about the nature of these predisposing factors would be helpful to guide the development of effective public health prevention and intervention programs to promote better sleep quality.

The hyperarousal model of insomnia: a review of the concept and its evidence

Primary insomnia is defined as difficulties in falling asleep, maintaining sleep or non-restorative sleep accompanied by significantly impaired daytime functioning in the absence of a specific physical, mental or substance-related cause. The current review provides substantial support for the concept that hyperarousal processes from the molecular to the higher system level play a key role in the pathophysiology of primary insomnia. Autonomous, neuroendocrine, neuroimmunological, electrophysiological and neuroimaging studies demonstrate increased levels of arousal in primary insomnia during both night and daytime. In the light of neurobiological theories of sleep-wake regulation, primary insomnia may be conceptualized as a final common pathway resulting from the interplay between a genetic vulnerability for an imbalance between arousing and sleep-inducing brain activity, psychosocial/medical stressors and perpetuating mechanisms including dysfunctional sleep-related behavior, learned sleep preventing associations and other cognitive factors like tendency to worry/ruminate.

A community-based study of insomnia in Hong Kong Chinese children: Prevalence, risk factors and familial aggregation

OBJECTIVES

There has been limited data on familial aggregation of insomnia. We aimed to explore the prevalence, risk factors and familial aggregation of childhood insomnia with a large community-based sample.

METHODS

A community-based epidemiologic study of sleep disorders was conducted among primary school children. Those children with at least one reported biological parent were recruited. A total of 5695 children (mean age 9.2; SD 1.8), 4939 of their reported biological mothers (mean age 38.9; SD 4.6) and 4289 of their reported biological fathers (mean age 43.3; SD 5.5) were studied.

RESULTS

The rates of insomnia 3 times/week in the past 12 months were 4.0%, 12.8% and 9.7% for children, mothers and fathers, respectively. A robust familial aggregation of insomnia was found even after adjustment of the shared environmental and socio-demographic factors. There was a significant dose-response relationship among the children across their parental status from neither, fathers, mothers to both parents with insomnia [3.0%, 7.1%, 9.5% and 11.9%; with ORs (95% CIs)=2.48 (1.82-4.37) for fathers, 3.42 (2.55-4.59) for mothers and 4.42 (2.42-8.10) for both parents, respectively]. In addition, the frequency of insomniac symptoms of the parents also had a dose-response effect on the rate of insomnia of their children.

CONCLUSIONS

Insomnia is a common problem in both children and their parents. A significant familial aggregation of childhood onset insomnia was seen in this study even after adjustment of the co-risk factors. There was a dose-response effect of parental insomnia on the rate of insomnia of their children with a slight predilection of maternal influences.