A study of 4,855 people by researchers at the Mayo Clinic, in the U.S. compared those with and without Alzheimer's disease in an attempt to find a genetic link to the condition. Genetic variations can be found on both chromosomes (XX in women and XY in men), one chromosome or not at all. The most significant new variation the researchers found was of a gene called PCDH11X on the X chromosome. The odds ratio of developing Alzheimer's (where 1 is the average risk) was 1.75 for women with two copies, 1.26 for women with one copy and 1.18 for men with one copy. Although statistically significant this is less than the odds ratio for the most significant Alzheimer's gene yet discovered APOE4 which has odds ratios of 11.5 for two copies and 4.8 for one.
You can find out more about this research by clicking on the link in this post.