Posted on behalf of Roberta Kwok

Scientists have found the first late-onset Alzheimer’s genetic risk factor specifically linked to women, but it doesn’t necessarily explain why more women get the disease.

The gene is PCDH11X, and it’s found on the X chromosome. That’s bad news for women, who carry two X chromosomes while men only have one. According to the study, published in Nature Genetics, the high risk only kicks in if the patient has two copies of a particular PCDH11X variant.

“What you have in a nutshell is the first study showing a gene on the X chromosome and the first sex-specific effect [for Alzheimer’s],” senior investigator Steven Younkin, a consultant-researcher at the Mayo Clinic’s Florida campus, told HealthDay. “It does not mean women are at increased risk for Alzheimer’s.”

The Mayo Clinic team discovered the gene by performing genome-wide analyses of 844 people with Alzheimer’s and 1,255 without. While women and men with only one copy of the PCDH11X variant had some increased risk of the disease, the risk went up considerably for women with two copies. The team confirmed their findings on another 1,547 Alzheimer’s patients and 1,209 control subjects (Mayo Clinic press release).

Compared with non-carriers of the gene, women with two copies were 75% more likely to develop Alzheimer’s.

The results make intuitive sense because more women tend to get the disease than men. But the imbalance could be explained by other factors, experts say. Rebecca Wood with the Alzheimer’s Research Trust told the BBC that “two-thirds of people with dementia are women, but this is partly because women live longer and risk of developing dementia increases with age.” And Younkin notes that other male-specific risk factors might balance out the increased risk for women (AFP).