In subgroup analyses stratified by ethnicity, we failed to find any significant associations between the CTSD C224T polymorphism and AD risk in the Asian (CT vs. CC: OR = 0.971, 95% CI = 0.626-1.506, P = 0.895; CT + TT vs. CC: OR = 0.954, 95% CI = 0.616-1.477, P = 0.833, Table 2) and Caucasian(CT vs. CC: OR = 1.139, 95% CI = 0.974-1.331, P = 0.102; CT + TT vs. CC: OR = 1.154, 95% CI = 0.982-1.357, P = 0.082, Table 2) populations. Here, CTSD is linked to Alzheimer disease.