DNA-based prediction of human externally visible characteristics in forensics: Motivations, scientific challenges, and ethical considerations

https://doi.org/10.1016/j.fsigen.2009.01.012Get rights and content

Abstract

There will always be criminal cases, where the evidence DNA sample will not match either a suspect's DNA profile, or any in a criminal DNA database. In the absence of DNA-based mass intelligence screenings, including familial searching (both of which may be restricted by legislation), there is only one option to potentially avoid or retrospectively solve “cold cases”: the DNA-based prediction of human externally visible characteristics of an unknown person based on the crime scene sample left behind. Predictive DNA markers are expected to be available for some group-specific appearance traits in the near future; although it is unlikely that we will soon be able to understand the biological complexity of individual-specific appearance. In suspect-less cases reliable DNA-based prediction of broader externally visible characteristics from crime scene samples are expected to reduce the potential pool of suspects by allowing police investigations to concentrate on specific groups of people. Here, we aim to describe the forensic motivations for DNA-based prediction of human externally visible traits as well as the scientific challenges of finding predictive DNA markers, and will discuss examples with promising (e.g. sex, eye color and hair color), as well as less promising expectations (e.g. adult body height), in the foreseen future. Despite the complex ethical and legal implications arising from DNA-based prediction of externally visible characteristics, we argue that their use does not lead to a violation of privacy. We suggest that likelihood-based results, rather than DNA data itself, should be provided to the police for investigative purposes avoiding data protection issues. Furthermore, we note that the risk of exacerbating social pressure on minority groups due to DNA-based prediction of externally visible traits in crime cases may be reduced rather than increased compared to a conventional eyewitness testimony. A firm legal basis will need to be established for the application of these promising qualitative techniques. To gain the attention of legislative bodies, we invite the forensic community to participate in a public discourse of these issues.

Section snippets

Forensic motivations for DNA-based prediction of externally visible characteristics

The current use of human DNA in the forensic context, i.e. for the purpose of individual identification relies strictly on comparative grounds: DNA profiles obtained from crime scene material are compared with those of known potential suspects. Similarly, in mass disaster or missing person cases, DNA profiles obtained from an unknown person are compared with those of known potential relatives, or with direct reference samples from items belonging to the missing person [1]. If matches between

Challenges in finding reliable genetic predictors of externally visible characteristics

Recent technological advances in microarray-based genotyping technologies, allowing parallel testing of up to over one million of genetic markers (usually single nucleotide polymorphisms, SNPs), together with theoretical advancement in association testing have provided powerful tools to find genes involved in complex including some EVC traits [7], [8]. Complex traits are defined as phenotypic characteristics that are influenced by several genetic and additionally by environmental factors.

Externally visible characteristics with promising expectation for accurate DNA prediction

The EVC that so far is most accurately predictable with DNA markers is human gender or sex. A length difference between the X-chromosomal and the Y-chromosomal copy of the amelogenin gene is useful for DNA-based sex determination [12], and this marker is included in most of the commercially available kits used for human identity testing in forensics. However, this prediction test is not error-free, and some males are wrongly diagnosed as females simply because they carry a Y-chromosomal

Externally visible characteristics with less promising expectation for reliable prediction

While iris color represents a limited complex trait with one major genetic factor (HERC2/OCA2, at least for blue and brown colors), and only a few additional minor genetic factors, human adult body height (or stature) turned out to be an EVC with much higher complexity. It would be desirable for forensic applications if one could accurately predict human body height from DNA samples since adult body height varies considerably within and between human populations. The amount of heritability of

Ethical and legal considerations for DNA-based prediction of externally visible characteristics in forensics

In most countries, the prediction of EVCs in forensic DNA analysis will add a new qualitative dimension to criminal investigations, since so far DNA evidence in forensics is only used quantitatively. With the notable exception of the Netherlands, where the use of DNA markers for EVC prediction (including prediction of geographic origin) is allowed and regulated by a law adaptation in 2003, no other country has introduced specific laws that would allow using this type of evidence in casework (as

Conclusions

Genetic (e.g. DNA-based) prediction of externally visible characteristics of an unknown person who left a DNA sample at a crime scene (or from an unidentified body) is expected to be useful for police investigation to reduce the number of possible suspects if no direct suspects can be identified by conventional means of investigations. Since externally visible traits of a person are known to everybody who has ever seen this person before, they cannot be considered as private information.

Acknowledgements

We thank Kaye Ballantyne for useful comments on the manuscript. The original research of M.K. on the genetic basis of human visible traits and their prediction mentioned in this article is supported by funds from the Netherlands Forensic Institute (NFI), the Erasmus University Medical Center Rotterdam, and by a grant from the Netherlands Genomics Initiative/Netherlands Organization for Scientific Research (NWO) within the framework of the Forensic Genomics Consortium Netherlands.

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