Environmental Triggers That Flip the Switch

My awakening to personalized medicine started about a year ago. I was attending a conference with an emphasis on Integrative Medicine when I heard the phrase for the first time, "Our genes are the gun and the environment pulls the trigger." It was an eye-opening experience. I wanted to learn everything about the relationship between the environment and genetic susceptibility to illness.

The genetic susceptibility to disease may be uncovered with studies in Single Neucleotide Polymorphisms (SNPs).¹ SNPs may cause subtle changes in a group of genes that under normal conditions are latent, i.e., they are switched "off." But when a person is exposed to precarcinogens or carcinogens, they can be switched "on," as described by the National Cancer Institute.^{2, 3} Prior to hearing about SNPs, I believed genetic risk was well-defined, versus being contingent upon the environment.

Some SNPs may have little or no effect on health while other SNPs may play a role in autism, multiple sclerosis, Alzheimer's, and cancer, just to name a few. According to the National Cancer Institute, "Such changes may eventually cause some people to be at higher risk for cancer, but only after exposure to certain environmental agents. They may also explain why one person responds to a drug treatment while another does not."⁴

The study of pharmacogenomics explores the genetic differences that affect a drug's safety and efficacy. This new data makes it possible for medical oncologists to use SNP profiling to personalize treatment decisions.^{5, 6}

"Although more than 99 percent of human DNA sequences are the same, variations in DNA sequence can have a major impact on how humans respond to disease; environmental factors such as bacteria, viruses, toxins, and chemicals, drugs and other therapies," as indicated by the US Department of Energy Genome Program.⁷

As researchers try to discover the etiology of complex diseases, they often study disease occurrence in identical twins. The National Institutes of Health found that environmental factors account for 55 percent of classic autism in twins.^{8, 9} In the journal Neuroscientist, it was noted that the likelihood of being diagnosed with multiple sclerosis (MS) is approximately 30 percent when the identical twin has MS.¹⁰ This data begs the question, how many complex health problems are the result of genetic susceptibility exposed to an environmental trigger?

As we evolve from research into practice, it will be important for healthcare practitioners to get acquainted with these SNPs. New information on genetic susceptibility will change our treatment model from "trial and error" to "personalized medicine." This information may also help patients recognize potential risk and guide lifestyle behaviors that keep the switch turned off.

References:

1. Genetics Home Reference. What are single nucleotide polymorphisms (SNPs)? Available at http://ghr.nlm.nih.gov/handbook/genomicresearch/snp.
2. National Cancer Institute. Slide 27: SNPs in Coding Regions - Subtle Changes in Proteins That Only Switch on Under Certain Conditions. Available at http://nci.nih.gov/cancertopics/understandingcancer/geneticvariation/page27.
3. National Cancer Institute. Understanding Cancer Series. Available at http://nci.nih.gov/cancertopics/understandingcancer/geneticvariation.
4. National Cancer Institute. Slide 12: Variations Causing Latent Changes. Available at http://www.cancer.gov/cancertopics/understandingcancer/geneticvariation/page12.
5. Genetic Science Learning Center. Personalized Medicine (Pharmacogenomics). Available at http://learn.genetics.utah.edu/content/health/pharma/.
6. Genetic Science Learning Center. Your Doctor's New Genetic Tools. Available at http://learn.genetics.utah.edu/content/health/pharma/intro/.
7. The U.S. Department of Energy Genome Programs. SNP Fact Sheet. Available at http://www.ornl.gov/sci/techresources/Human_Genome/faq/snps.shtml.
8. National Institutes of Health. Balance tips toward environment as heritability ebbs in autism? Available at http://www.nih.gov/news/health/jul2011/nimh-05.htm.
9. Isaac N. Pessah, Pamela J. Lein, Andrew W. Zimmerman. Evidence for Environmental Susceptibility in Autism. ResearchGate. Available at http://www.researchgate.net/publication/226141481_Evidence_for_Environmental_Susceptibility_in_Autism.
10. Gregory P. Owens, Don Gilden, Mark P. Burgoon, Xiaoli Yu, and Jeffrey L. Bennett. Viruses and Multiple Sclerosis. Neuroscientist. 2011 December; 17(6): 659–676. Available at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3293404/.