BackgroundThe intestinal microbiota was linked to autoimmune diseases. Graves' orbitopathy (GO) is an autoimmune disease that is usually associated with Graves' disease. However, information on the microbiome of GO patients is yet lacking. ObjectivesTo investigate whether GO patients differ from healthy controls in the fecal microbiota.DesignA cross-sectional study.Setting33 patients with severe and active GO and 32 healthy controls of Han nationality were enrolled between March 2017 and March 2018.MethodsThe Gut microbial communities of the fecal samples of GO patients and healthy controls were analyzed and compared by 16S rRNA gene sequencing.ResultsCommunity diversity (Simpson and Shannon) was significantly reduced in fecal samples from patients with GO as compared to controls (p<0.05). The similarity observed while assessing the community diversity (PCoA) proposed that the microbiota of patients with GO differ significantly from those of controls (p<0.05). At the phyla levels, the proportion of Bacteroidetes increased significantly in patients with GO (p<0.05), while at the genus and species levels, significant differences were observed in the bacterial profiles between the two groups (p<0.05).LimitationsSingle-centered study design and limited fecal samples.ConclusionsThe present study indicated distinctive features of the gut microbiota in GO patients. The study provided evidence for further exploration in the field of intestinal microbiota with respect to the diagnosis and treatment of GO patients by modifying the microbiota profile.