'Insomnia is all too often dismissed as being "all in your head". Our research brings a new perspective. Insomnia is also in the genes,' said study author Professor Eus Van Someren of Vrije Universiteit (VU) Amsterdam, the Netherlands.
About one in three adults in the UK suffers from insomnia, which is characterised by lasting problems falling asleep or by waking up at night. While the heritability of insomnia is estimated at 38 percent for men and 59 percent for women, previous gene association studies have been small and inconclusive.
The new gene association study, published in Nature Genetics, examined the genomes of 113,006 adults who reported symptoms of insomnia. The research team looked for genetic variation in the form of single nucleotide polymorphisms (SNPs) in more than 12 million genetic locations. They used data taken mainly from people older than fifty years via the UK Biobank, a resource of health data, genetic samples and questionnaire answers from more than half a million UK residents.
The researchers then compared the SNPs of the 32,384 people who reported usually experiencing insomnia against 80,622 controls. They assigned each SNP to a known gene and investigated the cumulative effect of the SNPs on insomnia through a genome-wide gene-based association study.
They found three loci and seven genes associated with insomnia complaints, with the most significant association for a gene called MEIS1. The gene has previously been implicated in the sleep disorders restless leg syndrome and periodic limb movement of sleep, suggesting that the genetic variants identified contribute to all three disorders. Genetic markers for insomnia also showed significant correlations with anxiety and depressive disorders, as well as metabolic traits including type 2 diabetes.
'This is an interesting finding, because these characteristics tend to go hand in hand with insomnia. We now know that this is partly due to the shared genetic basis,' said first author Anke Hammerschlag, also at VU.
Different genetic variants were involved in men and women, suggesting their insomnia may be caused by different biological mechanisms.
'We also found a difference between men and women in terms of prevalence: in the sample we studied 33 percent of the women reported to suffer from insomnia. For men this was 24 percent,' said senior author Professor Danielle Posthuma, at VU.
'The findings indeed open new doors for treatment in insomnia,' said Professor Van Someren. 'Finding risk genes are a first step toward finding underlying biological mechanisms. Only if we better understand these, it becomes likely that we can develop, for example, better drugs to give people the sleep quality that they miss so desperately.'