Ren et al. (2020) claimed that the abundance of genera Barnesiella and Alistipes negatively correlated with cognition ability. Tran et al. (2019) detected an association of Prevotellaceae and several butyrate-producing genera with Apolipoprotein E genotypes, which is the strongest genetic risk factor for Alzheimer’s disease. Nevertheless, it was reported that decreased abundance of the Lachnospiraceae family was associated with cognitive decline (Liu et al., 2019). The gene discussed is APOE; the disease is early-onset autosomal dominant Alzheimer disease.