Forensic analysis and law enforcement officers have many tools at their disposal to help solve crimes, including fingerprint analysis, ballistics, DNA typing and, more recently, forensic phenotyping of simple physical traits such as human eye and hair color. The forensic toolbox is ever evolving and capitalizing on new discoveries in genetics and molecular biology, allowing analysts to gather more information from a biological sample left at a crime scene and ultimately increasing our chance of catching criminals. What are some of the new technologies that we can expect to see in the not-too-distant future?
In his talk at the upcoming 24th International Symposium on Human Identification, Dr. Manfred Kayser will present some of these new tools and discuss how they will benefit efforts in human identification. One such tool is forensic phenotyping, which allows analysts to determine certain physical characteristics such as hair and eye color; I have discussed this topic at length in a previous blog entry. Other new technologies include the analysis of tissue-specific mRNAs and microRNAs (miRNAs) to identify body fluids deposited at a crime scene. Determining which RNAs are expressed in a biological sample can help identify the tissue and potentially help reconstruct or classify a crime (e.g., the presence of semen may support an allegation of rape). Scientists are painstakingly analyzing hundreds, even thousands, of genes to identify those that are tissue-specific and comparing detection technologies such as reverse transcription PCR (RT-PCR) or microarray analysis to determine which methods are the most reliable, sensitive and cost-effective. Because RNA is notoriously unstable, scientists are examining different types of RNA biomarkers for their ability to withstand assaults from the environment such as heat, humidity and exposure to ultraviolet light. I was surprised to learn that some tissue-specific RNAs are not as ephemeral as we are led to believe; some miRNAs can be detected by RT-PCR after one month at 15°C.
Another approach to tissue identification is examining patterns of DNA methylation. DNA methylation is one mechanism of epigenetic gene regulation, which involves heritable changes in gene expression that arise from changes in chromosomes without alteration of DNA sequence. DNA methylation patterns change throughout all stages of development, often in tissue-specific ways. In the future, scientists will use their knowledge of tissue-specific epigenetic markers to identify a body fluid or tissue found at a crime scene or the site of a mass disaster. In addition, they may be able to use these biomarkers to distinguish between monozygotic (i.e., identical) twins—something that current STR typing does not allow because monozygotic twins have identical genomic DNA sequences (except for rare genetic mutations that arise after zygote separation). Monozygotic twins have an increasing number of epigenetic differences as they age (1), making it possible to distinguish between them based on differences in DNA methylation. Because DNA methylation patterns change over time, epigenetic markers also may be useful in determining the age of the DNA donor.
Kayser will also speak about methods to estimate the age of a biological sample—how long ago was the sample left at the scene—and the time of day that the sample was deposited. He and other scientists are characterizing degradation patterns of a panel of biomarkers to learn how the degree of degradation can be used to estimate the number of hours, days, months or even years that have elapsed since the sample was deposited. They are also examining the utility of two circadian hormones, melatonin and cortisol, to learn whether the sample was deposited later at night, when melatonin levels peak, or earlier in the day, when cortisol levels are at their highest (2). This information can be important to help reconstruct the timeline of a crime or determine if a person was at the crime scene around the time that the crime was committed.
As these new technologies make their way out of the research lab and into your local crime lab, the amount of information that forensic analysts can glean from minute biological samples will increase, providing law enforcement officers with new tools to make apprehension of criminals easier and faster.
- Fraga, M.F. et al. (2005) Epigenetic differences arise during the lifetime of monozygotic twins. Proc. Natl. Acad. Sci. USA 102, 10604–9.
- Ackermann, K., Ballantyne, K.N. and Kayser, M. (2010) Estimating trace deposition time with circadian biomarkers: A prospective and versatile tool for crime scene reconstruction. Int. J. Legal Med. 124, 387–95.