Table 5. Microbiota and gut barrier alteration mechanism involved in IBS and FMS.

IBS=Irritable Bowel Syndrome; FMS=Fibromyalgia syndrome; FGIDs=Functional gastrointestinal disorders; EGC=Enteric glial cells; MC=Mast cells; NGF=Nerve growth factor; IBS-D=Irritable bowel syndrome with Diarrhea; mRNA=Messenger RNA; TLR=Toll-like receptors; VIP=Vasoactive intestinal polypeptide

Author	Year	Study design	Aim of study	Conclusions
Ivashkin et al. [22]	2021	Case-control	Evaluate the changes in gut microbiome and its components in IBS patients, and control patients as part of its pathogenicity.	Changes in the microbiome as result of persistent low-grade inflammation, impaired the gut permeability and exacerbate the IBS symptomatology.
Alciati et al. [29]	2021	Narrative	Summarize the updated information about FMS regarding diagnosis, pathogenesis, and treatment.	There is new information about the diagnosis, pathogenesis, and treatment of FMS that the physicians should be aware of to give the best options to these patients.
Erdrich et al. [8]	2020	Systematic Review	Identify the comorbidity of functional gastrointestinal disorders such as IBS in patients with FMS to discuss its implications.	There is a correlation between IBS in patients living with FMS, but there are more variations of FGIDs that could affect FMS patients. However, the data is not extensive to corroborate it.
Meira de-Faria et al. [21]	2020	Case-control	Investigate the interaction between EGC and mast cells in IBS and how a gut-brain disorder is linked with increased intestinal permeability and mast cell activation.	There is an involvement of EGC and MC in the control of barrier function and a possible EGC-MC interaction that may alter IBS patients, producing permeability abnormality that contributes to the pathophysiology of IBS.
Xu et al. [3]	2017	Cross-sectional	Explore the role and interaction of nerve growth factors and mast cells in IBS pathophysiology.	The elevation of NGF in the mucosa and its interaction with mast cells and sensory nerve fibers may be a factor in the development of visceral hypersensitivity and impaired gut barrier function in IBS-D.
Dlugosz et al. [16]	2017	Case-control	Comparing the expression of specific toll-like receptors in patients with IBS vs. controls.	There is an increased mRNA expression of TLR such as 4, 5, and 9 in the mucosa of the jejunum of IBS patients due to the involvement of bacteria and abnormal immune response.
Bednarska et al. [2]	2017	Case-control	Determine the mast cell and vasoactive intestinal polypeptide (VIP) function in barrier regulation.	IBS patients had higher levels of VIP than controls, and the biopsies samples had higher levels of tryptase and larger numbers of mast cells.