Novel Genetic Patterns May Make Us Rethink Biology and Individuality
Nov. 7, 2013 — Professor of Genetics Scott Williams, PhD, of the Institute for Quantitative Biomedical Sciences (iQBS) at Dartmouth's Geisel School of Medicine, has made two novel discoveries: first, 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 second, some of the same genetic mutations occur in unrelated people. We think of each person's DNA as unique, so if an individual can have more than one genotype, this may alter our very concept of what it means to be a human, and impact how we think about using forensic or criminal DNA analysis, paternity testing, prenatal testing, or genetic screening for breast cancer risk, for example. Williams' surprising results indicate that genetic mutations do not always happen purely at random, as scientists have previously thought.
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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."
If our human DNA changes, or mutates, in patterns, rather than randomly; if such mutations "match" among unrelated people; or if genetic changes happen only in part of the body of one individual, what does this mean for our understanding of what it means to be human? How may it impact our medical care, cancer screening, or treatment of disease? We don't yet know, but ongoing research may help reveal the answers.
Christopher Amos, PhD, Director of the Center for Genomic Medicine and Associate Director for Population Sciences at the Cancer Center, says, "This paper identifies mutations that develop in multiple tissues, and provides novel insights that are relevant to aging. Mutations are noticed in several tissues in common across individuals, and the aging process is the most likely contributor. The theory would be that selected mutations confer a selective advantage to mitochondria, and these accumulate as we age." Amos, who is also a Professor of Community and Family Medicine at Geisel, says, "To confirm whether aging is to blame, we would need to study tissues from multiple individuals at different ages." Williams concurs, saying, "Clearly these do accumulate with age, but how and why is unknown -- and needs to be determined."
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http://www.sciencedaily.com/releases/2013/11/131107204241.htm
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