A high value of the biomarker p-tau/Aβ42 is closely related to the diagnosis of Alzheimer’s disease, and a higher abundance of Bacteroides and Blautia presents higher levels of p-tau/Aβ42 [71], and lower levels of Aβ42/Aβ40 in the CSF, indicating higher amyloid accumulation [72]. This evidence concerns the gene MAPT and early-onset autosomal dominant Alzheimer disease.