UniFrac analysis revealed that there was significant phylogenic difference between the two groups in the APP cohort (PD/APP+ and HC/APP+; p = 0.006 by PERMANOVA after UniFrac analysis) comparing to combinations including the non-APP cohort, such as PD/APP− and HC/APP− (p = 0.649 by PERMANOVA after UniFrac analysis). The gene discussed is APP; the disease is Parkinson disease.