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Monozygotic (MZ) twins and higher-order multiples arise when a zygote splits during pre-implantation stages of development. The mechanisms underpinning this event have remained a mystery. Because MZ twinning rarely runs in families, the leading hypothesis is that it occurs at random. Here, we show that MZ twinning is strongly associated with a stable DNA methylation signature in adult somatic tissues. This signature spans regions near telomeres and centromeres, Polycomb-repressed regions and heterochromatin, genes involved in cell-adhesion, WNT signaling, cell fate, and putative human metastable epialleles. Our study also demonstrates a never-anticipated corollary: because identical twins keep a lifelong molecular signature, we can retrospectively diagnose if a person was conceived as monozygotic twin., (© 2021. The Author(s).)

Study Objectives: (1) To determine the prevalence of snoring, breathing pauses during sleep and obstructive sleep apnoea syndrome in the United Kingdom (UK) and determine the relation between these events and obesity and other sociodemographic variables. (2) To compare and integrate this data with published UK population data., Methods: A total of 664 women and 575 men aged 18-100 years who formed a representative sample of the non-institutionalised UK population participated in an online interview survey directed by a previously validated computerised system., Results: Overall, 38% of men and 30.4% of women report that they snore at night. Furthermore, 8.7% of men and 5.6% of women state that they stop breathing at night. Comparing our data to published data from the 1990s, this study observes a highly significant increase in the rates of reported breathing pauses during sleep (sleep apnoea) in the UK over the last 20 years (p < 0.0001). In addition, we observe a highly significant increase in the prevalence of obesity (BMI>30) in the UK population between 1994 and 2015 (p < 0.0001). Integration of our data with NHS and public health England data on obesity confirms this increase., Conclusions: Our data demonstrate a significant increase in the rates of reported breathing pauses during sleep (sleep apnoea) and obesity in the UK over the last 20 years. Sociodemographic and behavioural changes have likely contributed to this. Moreover, our data also suggests that sleep disordered breathing (SDB) is widely underdiagnosed in the UK., (Crown Copyright © 2018. Published by Elsevier B.V. All rights reserved.)