After excluding two studies [22,29] which deviated from the HWE,no significant associations were found between the CTSD C224T polymorphism and AD risk in the Asian (CT + TT vs. CC: OR = 0.968, 95% CI =0.605-1.548, P = 0.891) and Caucasian(CT + TT vs. CC: OR = 1.165, 95% CI =0.981-1.383, P = 0.081). The gene discussed is CTSD; the disease is Alzheimer disease.