Verification and Evaluation of a miRNA Panel for Body Fluid Identification Using DNA Extracts, United States, 2019-2021

Although human identification through DNA analysis has reached a level of maturity in the Forensic Science field with regards to the sophistication of the techniques and confidence in the results, the equally important question of body fluid identification has lagged behind, and could still be considered to be in a rudimentary state. Current crime scene and in-laboratory methods utilize detection methods that exploit the properties of each biological fluid (e.g. phenolphthalin or TMB testing for blood, amylase detection for saliva, and urease tests for urine), but validated confirmatory techniques are largely limited to microscopic methods (i.e. identification of spermatozoa) or immunological methods, as seen in the widely used immunochromatographic commercial tests for blood, semen, and other biological fluids.
Thus, while there is widespread confidence in the DNA profile generated, there is often significantly less assurance in the identity of the body fluid that the DNA profile was developed from. It is common during trials for attorneys to categorically accept the STR analysis, but probe the forensic scientist on the source of the DNA that generated the profile. Because of this dichotomy, significant efforts have been made over the past fifteen years in order to develop forensic serological techniques of a more discriminatory nature.
Of late, there has been some work in the forensic science field in regards to exploring microRNAs (miRNAs) for a molecular-based, forensic body fluid identification method. MiRNAs are small structures that are 19-23 nucleotides long and regulate cellular processes through interactions with mRNA by regulating gene expression through translational suppression or cleavage of a targeted mRNA. miRNAs are highly conserved among organisms, indicating their importance in regulating biological processes. As such, some miRNAs can be consistently expressed in all human tissues, and others can be tissue-specific Because of the potential for tissue specificity, their small size and consequent inherent stability, miRNAs have been the subject of recent research interest as a potential forensic body fluid identification technique. They are found in extracellular fluids, and thus the application of unique miRNAs for forensically relevant body fluids is a distinct possibility.