A second X chromosome has been shown to confer resilience against disease emergence in mouse models of AD, possibly mediated by the candidate gene Kdm6a located on the X chromosome.16 The role of the X chromosome in mediating the risk of AD remains enigmatic and may be mediated by loci on the chromosome itself or other chromosomes, or may depend on the degree of gene expression. This evidence concerns the gene KDM6A and Alzheimer disease.