MiRNA Analysis in Forensic Science

RNA was first introduced into forensic literature in 1984 when post-mortem RNA synthesis was described. It took several more years until another study was conducted introducing gene expression analysis, and even then it wasn't until after crucial advances were made when gene expression analysis was adopted by forensic laboratories and further applications using RNA were explored. When these applications were tested, the potential use for RNA in the identification of body-fluids and wound age estimation was uncovered. Today, body-fluid identification via specific mRNA quantification is an established standard technique in many forensic laboratories.

Even though successful mRNA recovery and profiling from even aged samples has been demonstrated, mRNA stability and susceptibility to degradation has always been an issue for mRNA based gene expression analysis, and impaired mRNA integrity impacts the reproducibility of the results. This was expected to be especially problematic for forensic routine applications using mRNA, because biological stains from casework are often met with challenges such as moisture, UV light, temperature, etc., which would potentially degrade mRNA beyond usability. miRNA profiling has been shown to have potentially serious advantages over mRNA profiling. Due to their small size of about 22 nt, mature miRNAs are much more stable than mRNAs, which makes them decidedly less susceptible against fractionation by chemical or physical strain. MiRNA profiling also has greater discriminatory potential than mRNA profiling, and it is believed that miRNA could even outperform mRNA profiling when it comes to identification of mixed and/or heavily environmentally challenged stains.

Initial studies clearly show the potential of miRNA profiling for forensic science. In a study conducted in 2009, it was demonstrated that miRNA can be extracted from forensic samples. Using blood, saliva, semen, vaginal secretions, and menstrual blood, they created body fluid specific assays consisting of two differentially expressed miRNAs per body fluid which they used to successfully identify and discriminate each.  Menstrual blood could clearly be distinguished from non-menstrual blood and even sperm-free semen could reliably be detected.

Although more research is needed before using the analysis in the field, miRNA-profiling may become a very promising tool for forensic analysis



Source:
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Hair Analysis in Forensics

Hair analysis was initially used in the 1960s and 1970s to evaluate exposure to toxic heavy metals through the use of atomic absorption spectroscopy. At the time, it was not possible to examine hair for drugs because the methods weren't sensitive enough. Years later, the use of radioimmunoassay allowed for the detection of certain organic drugs in hair. Today, gas chromatography coupled with mass spectrometry is the method of choice and is routinely used to document drug exposure in forensic science. One major advantage of hair testing compared to blood or urine testing is that it has a larger window (weeks to months versus 2 to 4 days) and is therefore able to provide a long-term history of an individual's drug use. Hair samples are typically taken from the scalp, although it has been suggested that other locations, such as arm hair, pubic hair, or axillary hair, could be used for alternative sources of drug detection when scalp hair is not available. While it has been suggested, various studies have found significant differences in drug concentrations between scalp hair and these alternative sources. These differences are believed to be caused by better blood circulation, a greater number of apocrine glands, and a different growth rate.

The mechanism by which the chemicals are bound to hair is not exactly known, although several suggestions have emerged. It was suggested that diffusion enhanced by drug binding to intracellular components of hair cells such as the hair pigment melanin could be a cause. However, this would not be the only mechanism as, when tested, drugs are trapped into the hair of albino animals, which  lack melanin. Another proposed mechanism was the possibility of the drug binding with certain sulphydryl-containing amino acids and diffusing into the hair cells. The abundance of amino acids such as cysteine form cross-linking disulfide bonds, which would bind the drugs. Various studies have also demonstrated that when given the same dosage, black hair tends to incorporate a greater amount of the drugs when compared to blond hair. This gives rise to discussions about a possible genetic variability of drug disposition in hair.

Of course, much more research is required before all questions surrounding hair drug testing can be satisfied, but it seems that hair analysis for the identification of drug use is quickly gaining recognition. Hair analysis could be a very useful tool to use in conjunction with conventional drug testing in toxicology.