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Genetic factor in Alzheimer's

16th January 2009

Researchers have implicated a gene in late onset Alzheimer's disease, pinpointing a genetic risk factor which is only carried by women.

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This is the first time that a genetic basis has been found for the fact that more women than men tend to develop Alzheimer's disease.

The gene variant resides on the X chromosome, of which women have two copies.

The US-based Mayo clinic undertook a detailed analysis of the genes of patients with Alzheimer's disease.

A variant of a gene known as PCDH11X appeared to be associated with higher Alzheimer's risk, according to the study, which was published in the journal Nature Genetics.

Upon analysis, it turned out that the gene's associated risk was mainly tied to women, with a very low probability in men.

Men had only one copy of the gene variant, since they carry only one X chromosome.

Women carrying only one copy of PCDH11X were also found to be at less risk for Alzheimer's disease.

When women carried two copies of the gene inherited from both parents, the raised risk was much more significant.

The gene variant PCDH11X controls protocadherin production.

Protocadherin is one of several molecules necessary in the communication of nerve cells with one another.

Protocadherins, according to some evidence, may be broken down by an enzyme linked to some types of Alzheimer's disease.

Lead researcher Steven Younkin said that many genes probably contributed to an overall risk of Alzheimer's, age being a more significant factor.

He said it was exciting to find a new gene for Alzheimer's, particularly the first that has a gender-specific effect, but that there was more work to do in resolving the complex genetics of the disease.

Rebecca Wood, of the Alzheimer's Research Trust, said that the research was important, and that finding genes associated with Alzheimer's will tell researchers about the biology of the disease, which could lead to new treatments being developed. At present, the cause of the disease is thought to be a mixture of genetic and environmental factors.

She said that two thirds of people with dementia are women, but that this was partly because women live longer anyway, and the risk of developing dementia increases with age.

Neil Hunt of the Alzheimer's Society said that the occurrence of dementia in women over 65 is twice that of men.

He said that it is likely that a combination of factors cause Alzheimer's disease, including genetics, age being the biggest risk factor.

According to current estimates, 700,000 people in the UK have dementia.

 

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