Inclusion Criteria:  Diagnosis of MMD by DSA according to the Japanese guidelines published in 2012, Stenosis or occlusion of the terminal internal carotid and the proximal middle and anterior cerebral arteries and unilateral or bilateral involvement Age: 2-60 years old.  Exclusion Criteria:  Moyamoya syndrome, Pregnancy, Evidence of gastrointestinal infection/ inflammation/ obstruction History of partial or total resection of small or large bowel, as well as gut reanastomosis, Use of antibiotics within 2 weeks prior to symptoms onset, Gastrointestinal malignancy Any hospitalization within 3 months before recruitment