Scientists uncover genetic ”hotspot” for breast cancer risk

February 16th, 2009 - 1:51 pm ICT by ANI  

London, Feb 16 (ANI): Scientists at Vanderbilt-Ingram Cancer Center have uncovered a new genetic “hotspot” that is linked with breast cancer susceptibility in Asian women.
Dr. Wei Zheng, who led the research team, has revealed that this region is on chromosome 6.
The researcher said that the genetic “locus” might help guide efforts to find the specific genes linked with non-inherited forms of the disease.
Genetics have a major role to play in breast cancer, and scientists have already identified a few of breast cancer susceptibility genes - such as BRCA1 and BRCA2. Mutations in such genes increase risk of inherited forms of breast cancers. “But the genetic factors identified so far explain only a small percent of all the cases in the general population,” Nature magazine quoted Zheng, an Ingram Professor of Cancer Research, professor of Medicine and the director of the Vanderbilt Epidemiology Center, as saying.
The genetic factors responsible for the vast majority of cases are unclear, “so there has been a lot of interest to identify additional genetic factors for breast cancer,” said Zheng.
For the study, the researchers focussed on a population of Asian women in Shanghai, China, which they had been studying for more than a decade to identify nutritional, environmental and genetic factors associated with disease risk.
By using “genome-wide association,” the researchers started searching for genetic variations in Asian women with breast cancer compared to healthy controls.
The investigators analysed more than 600,000 genetic markers - called SNPs (single nucleotide polymorphisms) - for differences between the groups.
From the first group of more than 3,000 women, they selected 29 of the most promising SNPs associated with breast cancer. Then they narrowed down these 29 candidate SNPs to a single SNP that exhibited strong and consistent association with breast cancer.
They also found a similar association in an independent group of American women, indicating that the results might be relevant for other ethnic populations.
“This SNP explains about 18 percent of the (breast cancer) cases in the general population. Compared to other previously identified SNPs, “this one would probably rank as No. 1 or No. 2 in terms of effect size,” said Zheng.
If a woman has just one copy of this SNP, her risk of breast cancer increases about 40 percent. With two copies of this SNP, the risk increases about 60 percent.
The SNP lies on chromosome 6 in a part of the genome with no known genes, “upstream” from the gene that encodes the estrogen receptor 1 (ERa).
While ERa is known to influence breast cancer aggressiveness, the impact of this candidate SNP on ERa is unclear.
“At this point, we actually don”t know the function of this SNP we identified,” he said.
However, the SNP does appear strongly associated with ER-negative cases of breast cancer, which carry a worse prognosis than ER-positive cases.
Zheng said: “Eventually, we hope that we can use this model to identify high-risk women for chemoprevention or regular cancer screening to reduce their breast cancer mortality.”
The study has been published in the journal Nature Genetics. (ANI)

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