Abstract
"INTRODUCTION: Insomnia is a prominent sleep disorder that impacts lifetime morbidity, with substantial socioeconomic costs. In high-income countries, insomnia prevalence is steadily increasing. However, little is known about insomnia in less urbanised, lower-income populations. Baependi is a rural town in the Brazilian heartland known to maintain day-night sleep cycles aligned to natural daylight availability despite electrification. This study aimed to investigate the prevalence and genetic epidemiology of insomnia in the Baependi cohort, utilising the Insomnia Severity Index (ISI) questionnaire. This cohort was also compared with an urban population, the São Paulo epidemiologic Study (EPISONO). The dimensionality of the ISI as a measure of insomnia was also evaluated.
METHODS: Mixed models were used for ISI score distribution and co-variate associations, and to compare subjective insomnia with quantitative sleep duration. Family structure was utilised to create polygenic models of insomnia heritability and manipulated for Genome-Wide Association Study (GWAS) and analysis of the candidate PER3 polymorphism. Factor analysis was performed to test the psychometric properties of the ISI.
RESULTS: Insomnia prevalence in the Baependi cohort was 7.3%, with numerous co-variate associations identified. Prevalence was higher in EPISONO, with notable differences in chronotype and depression. ISI score heritability in Baependi was 19%, and GWAS pinpointed CORO7 as a gene-of-interest. However, no significant association was found between PER3 genotype and ISI score. No definitive ISI factorial model was identified, but assessment of subjective insomnia and quantitative sleep duration did not show any notable disparities between the two measures.
CONCLUSIONS: This is the first study to describe ISI-reported insomnia distribution and to conduct genetic studies in a general population. Overall, this study provided insight into the complex foundations of insomnia. Evaluation of the ISI suggested it is a potentially suitable measure of insomnia in population studies, although some questionnaire items should be interpreted with caution. "