Possible reasons for these contradictory results include the small sample size of the Ntais study; the absence of an Asian population in the Schuur study; and the fact that the Bertram study only compared alleles T and C. Considering that those factors could contribute to bias in the final result, we updated the present meta-analysis which included a larger sample size to provide a more reliable correlation between CTSD C224T and AD. This evidence concerns the gene CTSD and Alzheimer disease.