If you haven’t read the previous article “When DNA Isn’t Enough – Part 1”, you should before you venture down below! In this article, author Coltan Scrivner explains his own research in this field.
The Basics of Methylation
DNA is composed of four nucleotide building blocks, A, T, C, and G. Throughout life, a methyl group – a carbon and three hydrogens – attaches to some of the C’s in your genome. This is known as DNA methylation, which is a big component of the larger phenomenon known as epigenetics. As it turns out, these methyl groups attach randomly to the C’s, though some evidence suggests that environmental conditions may play some part in this. In any case, the attaching of methyl groups to C’s is different among individuals – even identical twins. In fact, studies have shown that newborns already exhibit DNA methylation differences. Presumably, these differences would become more pronounced as time goes on. Not many studies have looked at this, but the ones that have also show evidence of greater discordance with age.
Taking the Practical Route
Compared to the SNP method, my project is less definitive. However, good protocols would still make the method definitive enough. Once you narrow the suspects down to two twins with normal DNA testing, you have two possible outcomes: a match between one twin and the sample at the crime scene, or inconclusive. At this point, you just need to differentiate between two people, not 7 billion. Thus, the required statistical power is much, much lower. The big difference between my method and the SNP method is the price. Whereas the SNP method costs over $100,000, my method could be done in-house for less than $5000. Furthermore, my method is performed using the same instruments as traditional DNA testing, meaning that the new instrumentation does not need to be validated for use in court.
Embracing DNA Methylation in Forensics
So, while it will take some work, and my project is more of a proof of concept study, the use of DNA methylation in forensics is generating a lot of attention. One of the issues with methylation in my study, i.e., different patterns in different tissues, has been a major benefit to a different use of DNA methylation – tissue identification. The idea here being that if you can identify consistent methylation patterns among a tissue type, you can use those patterns to identify the tissue. Another aspect that is relevant to my project, the increase in methylation with age, has been vetted as a possible investigative tool. If you can identify patterns of methylation that are consistent with different age groups, you can potentially “age” a suspect by their DNA methylation. Studies on methylation aging are few and far between, but preliminary results are promising, suggesting that age-based methylation analysis can get within 5 years (+/-) of an individual’s actual age.
As we learn more about DNA methylation, it will become more useful. This is true not only for forensics, but also medicine, since methylation plays an important role in turning genes “on” or “off.” This is particularly true in cancer, where abnormal DNA methylation seems to occur. But, before we try to cure cancer with methylation, perhaps we can perform the smaller task of telling two twins apart from each other.
Your Turn: What other promising, relevant studies have you read about? Contribute to the conversation — we’d be delighted to hear your thoughts.