Obstructive Sleep Apnea Appears Heritable, Whereas Daytime Sleepiness Is Mostly Caused by Environment

A study of pairs of twins revealed that obstructive sleep apnea (OSA) and measures of the disorder seem to be heritable, but daytime sleepiness is mostly influenced by environmental factors.

Previous family studies have found OSA to be heritable, but such studies have limited power to differentiate between heritable and acquired disorders, as family members share the same environment and may thus experience some of the factors that lead to disease (eg, diet and exercise). Twin studies, on the other hand, account for the shared family environment and are better able to identify purely genetic relationships. The existing literature on OSA features only 2 twin studies, one investigating snoring and the other based on results of a subjective self-reported questionnaire.

The current study, published in Respiratory Research, involved 71 pairs of twins in Hungary who completed the Epworth Sleepiness Scale (ESS) questionnaire, gave a medical history, and had their blood pressure and heart rate recorded. They then underwent an overnight polysomnography test that measured sleep stages, movements, oxygen saturation, electroencephalography readings, and more. Using these metrics, researchers calculated the apnea-hypopnea index (AHI), respiratory disturbance index (RDI), and oxygen desaturation index (ODI), which were used to identify the presence and severity of OSA.

Fifty-eight subjects (41%) were determined to have OSA; 44 had mild, 12 had moderate, and 2 had severe disease according to their AHI. Structural equation modeling was used to estimate the amount of variance from genetic and common environmental effects, and the researchers found evidence of genetic influence on all study variables, except for total sleep time.

OSA was found to be 73% heritable (P <.001), whereas the AHI, RDI, and ODI were 73%, 69%, and 83% heritable, respectively (P <.001 for all), meaning that the twins’ unshared environment explained the remainder of the variance. Scores on the ESS, however, were mostly determined by the environment, with just 34% of the variance accounted for by genetic factors.

The study authors identified some mechanisms that could account for the observed heritability of OSA, such as oropharynx diameter and tongue volume. They suggested that the environmental factors contributing to sleepiness could include poor sleep hygiene, work schedules, diet, and medications.

Knowledge of the high inheritance rate of OSA can help clinicians identify individuals whose relatives have sleep disorders and encourage them to receive screening and modify the controllable risk factors, such as obesity and smoking, that can predispose them to OSA.

“Due to the high public health importance of OSA, close relatives of patients with OSA should be screened to prevent OSA-related emergence of comorbidities and mortality,” they wrote.

The investigators recommended further research on the relationships among genes, environment, and sleep disorders via larger twin studies.

References

Szily M, Tarnoki AD, Tarnoki DL, et al. Genetic influences on the onset of obstructive sleep apnoea and daytime sleepiness: a twin study. Respir Res. 2019;20(1):125. doi: 10.1186/s12931-019-1095-x.