Genes and Environment Combined cause Disease

Kathleen Blanchard's picture
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Researchers say genes only partly explain how diseases develop. In order to personalize medicine, it will take more understanding of the interaction between genes and the individual's environment to predict diseases like cancer, diabetes and schizophrenia.

Scientists at Washington University School of Medicine in St. Louis conducted experiments showing gene variants alone may have little effect on understanding the chances of developing certain diseases. According to senior author Barak Cohen, PhD, a geneticist at Washington University School of Medicine..."if personalized medicine is going to work, we need to find a way to measure a human's environment."

Common Diseases only Partly Explained by Genes

"The effects of a person's genes – and, therefore, their risk of disease – are greatly influenced by their environment," Barak explains.

The researchers conducted a study in 2009 using the yeast Saccharomyces cerevisiae that grows naturally in vineyards and on the American oak tree. They wanted to know how the growing environment would change the speed of spore production.

The oak tree is more efficient at producing yeast spores. Four DNA variants, called single nucleotide polymorphisms (SNPs), added to each strain "interacted like crazy such that the combined effects...were always larger than the sum of their individual effects," Cohen says.

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In the study, the researchers used glucose to grow the yeast and they were able to predict how the spores would react using a statistical model to shuffle any combination of the four SNPs

For the current study Dr. Cohen and his team grew two yeast strains from oak trees, using 16 SNP variations grown in different sugars - glucose, fructose, sucrose, maltose, raffinose, grape juice, galactose and a mixture of sucrose, glucose and fructose.

The researchers found it was impossible to predict how the spores would produce because of the combined effect of genes and environment. Cohen explains, "And if we can't make accurate predictions about the way environment influences complex traits in yeast, then it will be exceedingly difficult to do so in people."

He adds, "These were all mono- or di-saccharides, so the environments are not radically different from one another," It's not like we heated up the yeast or froze them, added acids or put them in a centrifuge. We simply changed the carbon source and measured the effects of those four SNPs in the different environments."

Cohen concludes the way environment interacts with genes "may have a huge effect" on determining disease risk and response to medications. Molecular signatures that develop in childhood may play a role in chronic disease development.

He says incorporating metabolic readouts into statistical models could be useful for understanding a person's risk of cancer, diabetes and mental health disorders. Genes only tell part of the story. Measuring the environmental impact of genes and environment is an important step for bringing personalized medicine closer to reality.

PLoS Genetics, Sept. 2010 DOI: 10.1371/journal.pgen.1001144

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