28 Feb Genetics and Environment Influence Sleep Paralysis
MedicalResearch.com Interview with:
Alice Gregory PhD
Department of Psychology
Goldsmiths, University of London
Medical Research: What is the background for this study? What are the main findings?
Dr. Gregory: Sleep paralysis involves a total inability to move just as someone is falling asleep or waking up. This experience typically ends within seconds to minutes and is not usually a sign of any wider problem – yet it can be extremely frightening. This is in part because this experience is often accompanied by hallucinations.
To understand what is happening during episode of sleep paralysis it is useful to understand that there are different stages of sleep. One distinction is between Rapid Eye Movement (REM) and Non-Rapid Eye Movement (NREM) sleep. During REM sleep the body is paralysed. Dreaming often occurs during REM sleep, so it has been proposed that this paralysis keeps us safe, by preventing us from ‘acting out our dreams’. During an episode of sleep paralysis, someone may have woken up but has retained certain features of REM sleep (specifically the paralysis and sometimes dream-related hallucinations).
While sleep paralysis is rather common and the public seem incredibly interested in learning more about this, it is surprising that there is such little research on this topic.
Certain risk factors for sleep paralysis have been proposed previously, such as experiencing stress. However, those suffering from this experience are keen for more information, which is currently unavailable. For this reason, we wanted to see whether we could identify other factors which were associated with sleep paralysis.
Furthermore, in reviewing the literature, we were stunned that while it seems obvious that genetic differences between people are likely to be important in explaining why certain people experience sleep paralysis and others do not – there was almost no work on this topic. We decided to investigate this further as well.
Medical Research: What are the main findings?
Dr. Gregory: We asked over 800 people (many of whom were twins) about the frequency in which they had experienced sleep paralysis. We asked them about a range of other things that have either been linked to sleep paralysis previously (e.g. anxiety and sleep quality) or that we thought would make good candidates to further explore based on our reading of the literature (e.g. smoking and caffeine use). We also obtained DNA from many of these participants.
Our main findings were as follows:
1) Thirty percent of our participants reported experiencing sleep paralysis at least once in their lives. This percentage was higher than expected – but estimates from different studies do tend to vary quite extensively.
2) We found that sleep quality, anxiety symptoms and experiencing threatening life events were all independently associated with sleep paralysis. Our study cannot show that these things caused sleep paralysis (or indeed that sleep paralysis caused these things), but it would be interesting to try to understand exactly why there are these associations in the future.
3) We found that identical twins (who share all of their genes) were more likely to be similar in whether they had experienced sleep paralysis as compared to non-identical twins (who share only half of their segregating genes). We used this information to estimate that there is moderate genetic influence on sleep paralysis. From our study, it seemed that genetic and environmental influences appeared to be equally important in explaining why people differ in their experiences of sleep paralysis. Our sample was small, and more work is needed – but we were excited to be amongst the first to examine this important issue.
4) After highlighting the importance of genes in sleep paralysis, we examined some specific genes that have been linked to different aspects of sleep and the circadian system (or body clock). We found an interesting association between a genetic variant in the PER2 gene (which has previously been associated with diurnal preference – or the extent to which someone is a morning- or evening-type person; and aspects of sleep, such as quality). Our results should be considered very preliminary as our sample was particularly small – and our molecular genetic results were not statistically significant after accounting for the fact that we had also looked at a number of other genetic variants too.
Medical Research: What should clinicians and patients take away from your report?
Dr. Gregory: Our results are really preliminary and now need to be replicated in much bigger studies before the clinical implications are clear. However, it does seem from our study – together with a consideration of the wider literature, that stress and anything that disrupts the sleep cycle could potentially increase the chances of experiencing sleep paralysis. We need to examine this further, and it remains unexamined as to whether techniques that have been shown to be effective for lowing stress levels and aiding good sleep, such as mindfulness, could also have a knock on effect for reducing risk of sleep paralysis. Research on this topic is really in its infancy, and for sufferers it can be reassuring to know that: that this common experience has a name; they are not alone in having this experience; sleep paralysis often runs in families.
Medical Research: What recommendations do you have for future research as a result of this study?
Dr. Gregory: Sleep paralysis is common – but massively under-researched. Research that my colleagues and I have conducted on this topic (as compared to our work on other topics) seems to have received a disproportionate amount of attention from both the press and the general public. This emphasises the interest that there is in this topic. Further research is now needed to establish the causes of this experience. We need to know not just who is likely to experience sleep paralysis, but when the episodes are likely to occur. We also need to develop methods to prevent, or help people cope with these experiences which are terrifying for so many sufferers.
A twin and molecular genetics study of sleep paralysis and associated factors.
Denis D1,2, French CC1, Rowe R2, Zavos HM3, Nolan PM4, Parsons MJ4, Gregory AM1.
Alice Gregory PhD (2016). Genetics and Environment Influence Sleep Paralysis