Period 3 gene polymorphism and sleep adaptation to stressful urban environments

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.

The sex-dependent impact of PER2 polymorphism on sleep and activity in a novel mouse model of cranial-irradiation-induced hypersomnolence

Background

Hypersomnolence is a common and disruptive side effect of cranial radiotherapy and is associated with fatigue and disturbances in mood and cognition in primary brain tumor (PBT) patients. The biological underpinnings of this effect are not understood. Our laboratory has previously found that the presence of a single nucleotide polymorphism (rs934945, G-E mutation) in the PERIOD2 (PER2) clock gene was associated with a decreased likelihood of fatigue in PBT patients. Here, we aim to understand the effects of PER2 polymorphism on radiation susceptibility within a murine model of cranial-irradiation-induced hypersomnolence (C-RIH).

Methods

Male and female transgenic mice were generated using CRISPR-Cas9, replacing the endogenous mouse PER2:CRY1 binding domain with its human isoform with (hE1244 KI) or without the SNP rs934945 (hG1244 KI). Activity and sleep were monitored continuously 10 days before and after cranial irradiation (whole brain, 15Gy, single fraction). Behavioral assessments measuring anxiety, depression, and working memory were used to assess mood and cognitive changes 2 months postradiation.

Results

During their active phase, hE1244 knock-ins (KIs) had less radiation-induced suppression of activity relative to hG1244 KIs and female hE1244 KIs saw a reduction of hypersomnolence over 10 days. hE1244 KIs displayed less anxiety behavior and were more ambulatory within all behavioral tests.

Conclusions

The PER2 rs934945 polymorphism had long-lasting behavioral effects associated with radiation toxicity, particularly in sleep in females and the activity of all animals. Our findings shed light on biological mechanisms underlying C-RIH.

Daytime Sleep Disturbance in Night Shift Work and the Role of PERIOD3

STUDY OBJECTIVES

Recent evidence indicates that daytime sleep disturbance associated with night shift work may arise from both circadian misalignment and sleep reactivity to stress. This presents an important clinical challenge because there are limited means of predicting and distinguishing between the two mechanisms, and the respective treatments differ categorically; however, there is support that a polymorphism in the PERIOD3 gene (PER3) may indicate differences in vulnerability to daytime sleep disturbance in shift workers.

METHODS

We recruited 30 fixed night shift workers for laboratory assessments of circadian misalignment (dim light melatonin onset), sleep reactivity to stress (Ford Insomnia Response to Stress Test), daytime sleep disturbance (daytime Insomnia Severity Index), and PER3 genotype (PER3^4/4, PER3^5/-). The two mechanisms for daytime sleep disturbance (circadian misalignment and sleep reactivity to stress) were compared between PER3 genotypes.

RESULTS

Disturbed daytime sleep in the PER3^4/4 group was more likely related to sleep reactivity to stress, whereas disturbed sleep in the PER3^5/- group was more likely related to circadian misalignment. Exploratory analyses also revealed a blunted melatonin amplitude in the PER3^4/4 genotype group.

CONCLUSIONS

This study provides further evidence for multiple mechanisms (ie, circadian misalignment versus sleep reactivity to stress) associated with daytime sleep disturbances in shift workers. Additionally, it provides the new finding that PER3 genotype may play an important role in individual vulnerability to the different mechanisms of daytime sleep disturbance in night shift workers.

Post-Traumatic Sleep-Wake Disorders

All living organisms that face a traumatic life event are susceptible to sleep-wake disturbances. Stress, which can result in trauma, evokes a high level of physiological arousal associated with sympathetic nervous system activation, during both sleep and wakefulness. Heredity, sex hormones, early losses, developmental factors and intra- and interpersonal conflicts, contribute to the level of baseline physiological arousal, producing either subclinical, clinical or complex clinical traits, acutely and at any time after exposure to a traumatic event. The risk of acute sleep-wake disturbances becoming disorders and syndromes depends on the type of traumatic event and all of the aforementioned factors. Taken together, with consideration for behavioural and environmental heterogeneity, in research, will aid identification and understanding of susceptibility factors in long-term sleep and wakefulness pathology after exposure to traumatic events.