A later study confirmed that the abundance of A. muciniphila decreased in mouse models of AD alongside a reduction in the number of colonic mucus cells and an increase in serum levels of diamine oxidase (DAO), which reflects an impairment of intestinal barrier function; the administration of A. muciniphila effectively reduced serum DAO, reverted the loss of colonic mucus cells, promoted the reduction of pathogenic Aβ 40–42 levels in the cerebral cortex, and improved cognitive abilities in AD mouse models [48]. This evidence concerns the gene DAO and Alzheimer disease.