Gut microbiota signature in patients with Hashimoto’s thyroiditis framed in polyautoimmunity

Background A role for gut microbiota (GM) composition has been hypothesized in the pathogenesis and clinical presentation of different autoimmune disorders, including thyroid autoimmune diseases. No data are available about GM composition in patients showing Hashimoto’s thyroiditis (HT) associated with a further non-endocrine autoimmune disease and this was the aim of the present study. Patients and methods We examined the faecal microbial composition in 58 euthyroid adult patients (50F/8M) with HT subdivided in three groups: 24 with isolated HT (iHT); 22 with HT and gastric atrophy (HT+CAG) and 12 with HT and vitiligo (HT+VIT). None of the patients followed unbalanced diets, had other disorders, or used interfering drugs. Nineteen matched healthy subjects (HS) represented the control group. Microbiota composition was determined via sequencing of the hyper-variable region V3–4 of 16S rRNA gene on Illumina MiSeq platform. α- and β-diversity indices and all statistical analysis were computed in QIIME2. Results All patients showed increased relative abundance of Firmicutes spp. and Actinobacteria spp. (p<0.00001) and reduced relative abundance of Proteobacteria spp. and Bacteroidetes spp. compared to HS (p<0.001). Firmicutes/Bacteroidetes ratio was significantly higher in groups iHT, HT+CAG and HT+VIT than in HS (p<0.0001); to note, this ratio was higher in HT+VIT group than in iHT patients (p=0.046). α-diversity indexes (richness and phylogenetic diversity) were higher in every group than in HS (p<0.001 and p<0.0001). Phylogenetic distance (β-diversity) was clustered in all groups compared to HS. The LEfSe analysis, revealed that Lachnospiraceae, Peptostreptococcaceae and Bifidobacteriaceae, encompassing the bacterial species Fusicatenibacter saccharivorans , Anaerostipes hadrus and Blautia massiliensis , were significantly associated to patients with HT+VIT. In contrast, patients with HT+CAG were strongly associated to Lachnospiraceae and Streptococcaceae, with the prevalence of Streptococcus salivarius , whereas patients with HT were mostly associated to Blautia faecis , in accordance with ANCOM results. Conclusions Overall, our findings highlight significant differences in relative taxa abundances as well as phylogenetic distances of the GM communities between patients with Hashimoto’s thyroiditis isolated or associated to further autoimmune disorders (chronic atrophic gastritis or vitiligo), and healthy subjects. Interestingly, specific bacterial signatures were associated to the most common organ-specific autoimmune disorders concurrent with HT.