Szily M, et al. - Using the Hungarian Twin Registry (48 monozygotic, MZ and 23 dizygotic, DZ pairs, mean age 51 ± 15 years), researchers focused on the genetic influences on the onset of obstructive sleep apnoea (OSA) and daytime sleepiness by examining 71 Hungarian twin pairs. For OSA, a 41% prevalence was reported. OSA [defined by an apnoea hypopnea index (AHI) ≥5/h] was itself 73% heritable. The range of heritability of the AHI, oxygen desaturation index and respiratory disturbance index was between 69% and 83%. The remaining variance between 17% and 31% was explained by the unshared environmental component. Overall, the heritability of OSA and the indices of OSA severity was established in this study, while daytime sleepiness was shown to be affected mostly by environmental factors.