Scientists find sex gene risk for Alzheimer’s in certain females


New York: A gene found on the X chromosome harbours the first sex-specific genetic variant linked to a greater susceptibility to Alzheimer’s, according to a new study.

Researchers at the Mayo Clinic in Jacksonville, Florida and Rochester, Minnesota showed that women who inherited the same variant of the gene, known as PCDH11X, from both parents were far more likely to develop the disease.

Among Alzheimer’s patients evaluated for the study, “the odds a women had two copies of the PCDH11X variant as opposed to no copies was nearly twice as high as for the control group,” the lead researcher, Steven Younkin, told AFP by email.

Both men and women with only a single copy were also slightly more likely to have Alzheimer’s. But only women have two X chromosomes, making them uniquely vulnerable to the impact of the double variant.

Men have one Y chromosome, and one X chromosome.

Alzheimer’s is a degenerative disorder of the brain characterised by forgetfulness, agitation and dementia. There is no known cure.

While many gene variants, or alleles, have been implicated in the onset of the disease, only one other — APOE 4 — has been shown to be a higher risk factor.

The findings, published in the journal Nature Genetics, do not necessarily mean that women as a whole are more prone to getting Alzheimer’s.

“There may be male-specific risk factors — genetic or environmental — that balance the increased risk in women from PCDH11X variant,” Younkin explained.

The researchers discovered the wayward string of DNA by scanning the entire genome of 844 patients and 1,255 healthy persons, looking for telltale markers that might point to a genetic culprit.

After identifying PCDH11X, they confirmed the “highly significant association” by repeating the gene tests on an even larger group of 1,547 patients, and a slightly smaller number of controls.

Follow up studies will investigate the exact mechanism by which the variant affects the nervous system in order to help diagnose the disease early on and develop suitable drugs, Younkin said.

Alzheimer’s is caused by a massive loss of cells in several regions of the brain, driven by a buildup of plaques of amyloid protein. The disease occurs most frequently in old age.

An estimated 37 million people worldwide live with dementia, with Alzheimer’s disease causing the majority of cases, according to the World Health Organisation (WHO).

With the ageing of populations, this figure is projected to increase rapidly over the next 20 years.

Women witth fatter tums better able to deal with stress

Salt Lake City: Women who have extra fat around their middle may enjoy significant health advantages over slimmer hourglass-shaped females, says a 37-nation study in the journal, Current Anthropology.

Elizabeth Cashdan, a Utah University anthropologist, says that being thinner could mean missing out on the hormones that make women physically stronger, more competitive and better able to deal with stress.

Her study shows that across the world, women’s average waist-to-hip ratio is higher than the magic number of 0.7, the upper threshold of a classic hourglass figure – and the shape that anthropologists believe indicate female fertility to the opposite sex.

It is thought that bigger women have more androgens, a class of hormones that includes testosterone.Androgens increase the waist-to-hip ratio in women by boosting levels of visceral fat, which is carried around the waist. Raised levels of androgens are linked to increased strength, stamina and competitiveness in women, says Cashdan.

Trading the benefits of a thin waist for better ability to be independently resourceful may prove a good deal in many societies, she adds – and this in turn may alter male preferences.

Thus, in Japan, Portugal and Greece, where women tend to be less economically independent, the men say they place a higher value on a thin waist than do men in Britain or Denmark, where there tends to be more sexual equality.

And in some non-Western societies where food is scarce and women bear most of the responsibility for finding it, men prefer larger waist-to-hip ratios.

“Whether men prefer a waist-to-hip ratio associated with lower or higher androgen levels should depend on the degree to which they want their mates to be strong, tough, economically successful and politically competitive,” says Cashdan .