Beyond DNA: The Evolution of Forensic Identification
Is it time to replace STR DNA markers as the ultimate weapon for identification?
In an era where criminal ingenuity is on the rise, the imperative to enhance our identification techniques has never been more pressing. Since 1986, DNA analysis has stood as an indispensable tool, enabling the exoneration of an innocent individual falsely accused of a double child murder and rape case (Collin Pitchfork case). However, as time has advanced, so too have the complexities encountered by scientists and investigators in tackling intricate cases. Illustratively, we confront situations where a rape victim’s accusation of sexual misconduct is countered by the alleged perpetrator, asserting that the DNA found is not seminal but merely blood. Another challenge emerges with identical twins, who possess indistinguishable DNA profiles. Family members, particularly close relatives, further complicate matters by sharing highly similar DNA profiles. Stability of a biomarker also plays a crucial role in validating as a genuine biomarker and samples with degraded DNA has often been reported at different Forensic Science laboratories. In these scenarios, the call for alternative strategies becomes increasingly vital. This article explores the evolving landscape of forensic genetics and the pressing need to augment our identification methods in the face of contemporary challenges.
Molecular Origins: Unravelling the Source of DNA: Rise of proteomics:
The first challenge finds resolution in the distinct origins of various bodily fluids, each stemming from different organs within our bodies. For instance, blood corpuscles are a product of hematopoietic cells in the bone marrow, semen containing sperm originates from the male gonads or seminiferous tubules, and saliva is generated by the salivary glands in the buccal cavity, housing epithelial cells. These origins distinctly indicate the source of DNA. However, what distinguishes these bodily fluids at the molecular level? The answer lies in the intricate machinery inherent to each tissue, which facilitates diverse post-translational modifications to the resulting mRNA, consequently yielding distinct peptides. These modifications involve processes such as acetylation, methylation, and glycosylation, among others. As a result, while all cells may share the same DNA, the arrangement of peptides in different fluids diverges. The field of proteomics, employing specialized techniques like Mass Spectroscopy coupled with various analyzers including quadrupole and time-of-flight instruments, offers a means to scrutinize these peptide profiles. Thus, even in cases where the suspect claims the DNA originates from their blood, the peptide arrangement can unequivocally differentiate it from semen or other bodily sources.
Unravelling the Mystery of Identical Twins: Rise of whole genome sequencing:
In the second scenario, a different complexity arises when dealing with identical twins, scientifically known as monozygotic (MZ) twins. Identifying the specific twin involved in a crime poses a formidable challenge. This is due to the fact that MZ twins originate from the same fertilized egg cell, resulting from the union of a single sperm and egg cell, which then splits into two. To illustrate this challenge, consider a case where one of the twin brothers faces accusations of rape. In such instances, forensic evidence frequently revolves around germline-derived cells, particularly sperm cells. The primary objective here is to differentiate between one MZ twin and his sibling when connecting either of them to a sperm sample discovered at a sexual crime scene. Initially, it might appear that genetic or epigenetic identification in these cases necessitates having sperm samples from both twins as reference materials. This is because (i) distinguishing epigenetic markers in other tissues like blood or saliva might be erased during germline-specific reprogramming, and (ii) genetic alterations occurring in these non-germ cells may not be present in sufficient concentration in sperm. However, the enforcement of semen donation is not a commonly established practice in legal systems. Consequently, the reference tissue available in forensic cases usually does not align with the target tissue. Fortunately, advanced techniques such as whole genome sequencing (WGS) technologies have significantly enhanced the prospects of successfully attributing germline-derived cells to one of a pair of male identical twins within forensic investigations. WGS facilitates a comprehensive exploration of unique DNA sequence changes that occurred within a specific post-twinning timeframe, connecting critical tissue types of both adult twins from an evolutionary standpoint. These mutations serve as the sought-after distinguishing factors that are specific to one twin while not being overly tissue-specific.
Stability Beyond DNA: The Rise of miRNAs:
The stability of a biomarker is substantially influenced by its chemical structure and framework. Traditionally, DNA, with its duplex structure, has been regarded as a more stable biomolecule compared to RNAs. However, recent research has unveiled an exception in the form of a unique RNA class known as microRNAs (miRNAs), which has demonstrated even greater stability than mRNAs. For instance, miRNAs remain stable at room temperature in blood samples for nearly 24 hours, with certain fractions retaining stability even after 72 hours of incubation at room temperature. Notably, these molecules offer the potential for identification, leveraging their existing polymorphism.
Conclusion: A Glimpse into the Future
In conclusion, the introduction of alternative techniques, presents a promising frontier in the realm of identification in forensic science. Yet, despite their immense potential, several challenges loom over their practical incorporation into routine casework. Foremost among these challenges is the staggering caseload that most forensic laboratories grapple with. Adopting new identification techniques requires time and resources that many laboratories can ill-afford due to the relentless influx of cases. Furthermore, the effective implementation of these methods relies on well-equipped laboratories staffed by skilled scientists. Regrettably, this standard is not met universally, as numerous facilities struggle with underdeveloped manpower and resource limitations. However, these challenges should not diminish our enthusiasm for the possibilities offered by these advanced techniques. Rather, they should spur a collective effort in the scientific and forensic communities to overcome these hurdles. With sustained research and advancements, it’s possible that a future exists where these alternative markers become more accessible and feasible for routine use in criminal identification. In the interim, the forensic community should explore innovative ways to streamline and optimize laboratory processes and increase access to advanced technology. Collaborative efforts, investment in infrastructure, and the development of a skilled workforce are imperative to make the adoption of these alternative techniques a reality.
The journey ahead may be arduous, the potential for more effective and accurate criminal identification justifies the endeavor. Perhaps, the door to the future of forensic science has been nudged ajar; it is our responsibility to push it open.
Author:
Nilanjan Saha
