These genetic factors partially explain the differing rates of alcohol dependence among racial groups.[84][85] The alcohol dehydrogenase allele ADH1 B*3 causes a more rapid metabolism of alcohol. The allele ADH1 B*3 is only found in those of African descent and certain Native American tribes. African Americans and Native Americans with this allele have a reduced risk of developing alcoholism.[86] Native Americans, however, have a significantly higher rate of alcoholism than average; it is unclear why this is the case.[87] Other risk factors such as cultural environmental effects e.g. trauma have been proposed to explain the higher rates of alcoholism among Native Americans compared to alcoholism levels in caucasians.[88][89]