Recently, Nakano et al. have reported that intracerebral hemorrhage occurred more frequently in mice exposed to Streptococcus mutans, a major member of oral streptococci related to dental caries, with the cnm gene (cnm-positive S. mutans) than to mice exposed to the same organism lacking the gene, and suggested that exposure to cnm-positive S. mutans is a novel risk factor for cerebral hemorrhage in humans10. This evidence concerns the gene MTM1 and dental caries.