###### Abstract  
Background: Obstructive sleep apnoea (OSA) and gut dysbiosis are known risk factors for atherosclerosis. However, only very few studies have been focused on the relationship between OSA, atherosclerosis, and the intestinal microbiome, all in animal models. Methods: Twenty-two patients with OSA, 16 with and 6 without carotid atherosclerosis were involved in the study. After a diagnostic sleep examination, the intima media thickness (IMT) was measured and plaques were found using carotid ultrasound. Blood was also drawn for metabolic profile, and a stool sample was provided for 165 ribosomal RNA microbiome investigation. Results: An increased maximal common carotid artery (CCA) IMT was significantly associated with decreased phylum-level diversity. The level of _Peptostreptococcae_ was significantly lower in atherosclerotic subjects. Some other candidate microbes appeared in the two groups at the genus level as well: _Bilophila_, _Romboutsia_, _Slackia_, and _Vellonella_ in the non-atherosclerotic group; and _Escherichia-Shigella_, _Prerotella_, and _Ruminococcae_ in the atherosclerotic group. Conclusions: This is the first pilot research to analyze the association between the gut microbiome and atherosclerosis in adult patients with OSA with and without carotid atherosclerosis. Dysbiosis and individual bacteria may contribute to the development of carotid atherosclerosis in patients with OSA. Further investigations are necessary to reveal a more precise background in a larger sample.  
Keywords: gut microbiome; alpha diversity; intima-media thickness; carotid atherosclerosis; ultrasound; sleep apnoea; sleep disorder +
Footnote †: journal: Medical Imaging Centre, Semmelweis University, 1082 Budapest, Hungary 1  
to those with normal IMT levels, a significantly higher proportion of _Prevotellaceae_ was discovered. Despite the fact that the Moscow study claimed that a higher IMT was discovered in the cluster with less diversity, we did not find a statistically significant difference in alpha diversity between the two groups [5]. Individual species have been studied to see if _Akkermansia muciniphila_ has anti-atherogenic properties [6]. Furthermore, the genus _Collinsella_ was concentrated in individuals with symptomatic atherosclerosis, whereas _Roseburia_ and _Eubacterium_ were enriched in healthy participants [7]. Atherosclerosis and the gut microbiome have a link that is thought to be influenced by lifestyle factors, most particularly the diet [3]. However, in the presence of confounding OSA, the effect of chronic intermittent hypoxemia must be considered. On one hand, hypoxemia affects the growth of certain gut bacteria [8]. On the other hand, it directly correlates with atherosclerosis via hypertension, dyslipidemia, and vascular inflammation [1]. Therefore, studies on atherosclerosis and gut microbiome cannot directly be translated to patients with OSA.  
So far, only a few research teams have published their findings from studies on the relationship between OSA and the intestinal microbiota [9; 10; 11; 12; 13], with only two of them focusing on adults [9; 10]. The link between OSA, atherosclerosis, and the gut microbiome has only been studied in a small number of researches, to the best of our knowledge, all in mice animal models [14; 15; 16; 17].  
This study's aim was to explore the relationship between adult OSA patients' gut microbiome and atherosclerosis which is essential to find gut dysbiosis-targeted treatments that may be used as an adjunct to traditional OSA treatment and may result in advantages for OSA morphologies.