[Although we did a small study], there is a lot more going on than we thought, and the results are, in some ways, astoundingly weird.
Professor of Genetics Scott Williams, PhD
Researchers at Dartmouth Geisel School of Medicine (USA) have made two novel discoveries: 1) a person can have several DNA mutations in parts of their body, with their original DNA in the rest (resulting in several different genotypes in one individual); and 2) some of the same genetic mutations occur in unrelated people.
Background: We think of each person’s DNA as unique. Genetic mutations (changes) can occur in cells that our passed from parent to child, sometimes causing birth defects. Other genetic mutations occur during childhood or adult life, after exposure to sunlight, radiation, or other carcinogens (cancer-causing agents). These later or “somatic” mutations do not affect sperm or egg cells, so they are not passed on to children. Somatic mutations can cause disease, including cancer, but do not always do so. However, if the mutated cell continues to divide, the person can develop tissue with a different DNA sequence from the rest of her body.
The Study: Because somatic changes are thought to happen at random, scientists do not expect unrelated people to exhibit the same mutations. Williams and colleagues analyzed the same 10 tissue samples in two unrelated people. They found several identical mutations, and detected these repeated mutations only in kidney, liver and skeletal body tissues. Their research examined “mitochondrial DNA” (mtDNA) — a part of DNA that is only inherited from the mother. Technically all women would share mtDNA from one common female ancestor, but mutations have resulted in differences. The importance of Williams’ finding is that these tissue-specific, recurrent, common mutations in mtDNA among unrelated study subjects — only detected in three body tissues — are “not likely being developed and maintained through purely random processes,” according to Williams. They indicate “a completely different model …. a decidedly non-random process that results in particular mutations, but only in specific tissues.”
My Take: So if an individual can have more than one genotype, does it alter our concept of what it means to be a human, and impact how we think about forensic or criminal DNA analysis, paternity testing, prenatal testing, and genetic screening for cancer? Genetic mutations may not always happen at random, as we previously had thought. We are diverse beings in that a single person is genetically not a single entity. So what makes us an individual? Genes? Gene expression? Memory? I’m Dr. Michael Hunter (or at least that’s who I think I am!).
The small print: The material presented herein is informational only, and is not designed to provide specific guidance for an individual. Please check with a valued health care provider with any questions or concerns. As for me, I am a Harvard- , Yale- and UPenn-educated radiation oncologist, and I practice in the Seattle, WA (USA) area. I feel genuinely privileged to be able to share with you. If you enjoyed today’s offering, please consider clicking the follow button at the bottom of this page.
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References: David C. Samuels, Chun Li, Bingshan Li, Zhuo Song, Eric Torstenson, Hayley Boyd Clay, Antonis Rokas, Tricia A. Thornton-Wells, Jason H. Moore, Tia M. Hughes, Robert D. Hoffman, Jonathan L. Haines, Deborah G. Murdock, Douglas P. Mortlock, Scott M. Williams. Recurrent Tissue-Specific mtDNA Mutations Are Common in Humans. PLoS Genetics, 2013; 9 (11): e1003929 DOI:10.1371/journal.pgen.1003929; The Geisel School of Medicine at Dartmouth (2013, November 7). Novel genetic patterns may make us rethink biology and individuality.ScienceDaily. Retrieved November 11, 2013, from http://www.sciencedaily.com/releases/2013/11/131107204241.htm