Fall 10 Epigenetics and Forensics

 I am not an expert. This is by no means a perfect example of methodologies, but rather a fake scenario to provide a basic idea of how epigenetics can possibly help solve crimes:

Lets say a forensic specialist is working a case in Arizona about a suspected serial killer. The police have followed evidence to a residence with two suspects who live together, but they are identical twin brothers. Who is our killer?  We find a kitchen knife with three sets of DNA on it. Both twins use the knife at home for cooking. Having the same DNA, how would you know which brother the killer is, and who is our 3rd person? Epigenetics offers many solutions to help identify suspects as well as victims.

Fluid identification: Epigenetics can identify what type of fluid the DNA came from, such as blood, semen, vaginal, sweat, or saliva. Through examining the epigenetic methylation profiles, we can tell that much of the DNA from the knife came from male sweat, which we would expect on the kitchen knife. However, one set also came from male semen, and the last DNA set came from vaginal fluid. As our two suspects are males with identical DNA, there is certainly a third person, female, to consider here. In our investigation we may decide that the semen DNA, which belonged to one of the males, is more likely to belong to our suspect, so we decide to focus on that one. 

Twin identification (part one): Now the question is, with identical DNA, which twin did it? Since we decided to focus on the semen DNA sample, we look closer at the epigenome on it, which may lead to our killer. The epigenome tells a story about habits and environment. Is one twin a smoker? Do they have a different diet? Does one exercise while the other doesn't? Perhaps they have a job with environmental toxins. The epigenome can tell two identical twins apart by such differences in habit and environment. 

Diet identification: Both of our suspects are non-smokers, get the same amount of exercise, have the same basic environment, but from the sweat and semen samples we can see that one is a vegetarian and the other only eats meat. We know this in part because broccoli contains sulforaphane, which turns off oncogenes (cancer causing genes), via the epigenome. By looking at the epigenome of our semen sample, we determine the suspect has their cancer genes turned on, thus is not a fan of vegetables. Our suspect is the meat eating twin. But which twin is for sure the carnivore?

Twin identification (part two): Since epigenomes are unique, we can verify our I.D. by comparing a fresh sample of both their epigenomes with the semen one found on the knife, and we now know which twin is the carnivore killer.

Confronted with the evidence, our killer decides to brag about a recent victim, but refuses to say who she is or where the body is buried. How can we find more information?

Victim identification: We found a victims fluid on the knife, but without a body, who could it be? Through epigenetics we can compile a profile of their life. Epigenetics can give a good idea on age, body shape, weight, habits, environment, socioeconomic status, where they lived, etc. It provides information that DNA alone cannot, and in many ways can be more useful. If our victims DNA is not in the data base, we can use epigenetic profiling to search through our missing persons list, narrowing down possibilities. 

Our epigenetic profile from the fluid sample suggests a 30-35 year old female, smoker, little exercise, pear shaped body type, moderately obese, heavy drinker, no drug use, and is regularly exposed to some form of toxins. From our missing persons list we find a 33 year old woman who fits the physical description. A neighbor confirms the smoking and drinking patterns, and that our missing person worked as a pest control specialist. To verify our hunch, we now can perform a regular DNA test between a sample of hair we found at her home, with the DNA from the knife, and positively I.D. our victim. 

The police confront our killer with a photo of the newly identified victim. In a moment of shock, he reveals the location of the body. Our seemingly impossible case is now closed, justice will be served, and future lives saved thanks to epigenetics. Here is a more in depth video on the subject: