While our bodies age, scientists believe that our DNA remains constant. New research, however, reveals that subtle chemical changes occur to our DNA as we age, even though its sequence remains constant — and it could explain why the risk of developing diseases increases as we get older.
DNA is made up of four basic chemical building blocks called adenine, thymine, guanine and cytosine. It's the sequences of those chemicals in a strand of DNA that determines what function a gene has, and one of the ways the resulting genes are controlled is a process called methylation. That just means that a methyl group — one carbon atom and three hydrogen atom — bonds to part of the DNA and subtly change its function.
But new research, published in PNAS, shows that our DNA's susceptibility to methylation changes as we get older. A team of researchers from the Bellvitge Biomedical Research Institute in Barcelona, Spain, extracted DNA from white blood cells of 20 newborn babies and 20 people aged between 89 and 100 years old, then compared their respective degrees of methylation.
In a newborn baby, 73 per cent of cytosine nucleotides were methylated, while in centenarians that figure rose to 80.5 per cent. An intermediary example, taken from a 26-year-old male subject, exhibited 78 per cent methylation. It's not clear why it happens, but the researchers speculate that it could be due to extremely subtle age-related changes to the DNA.
But what the hell does it all mean? Well, taking a closer look at the samples, the researchers discovered that a third of the methylated groups that were different in the elderly compared to the young are already known to be linked to cancer risk.
If you think about the DNA strand as "hardware" and the added methyl groups as "software" — which isn't actually a bad analogy — you can think of the inappropriately placed methyl groups as software bugs that accumulate with age. It's just that, for humans, those bugs lead to increased risk of terminal disease. Fortunately, these kinds of findings should help scientists troubleshoot our internal apps. [PNAS via Science]