To Sketch a Thief: Genes Draw Likeness of Suspects

The old-fashioned police sketch is getting a makeover.

Researchers are identifying genes that give rise to a person’s physical traits, such as facial structure, skin color or even whether they are right- or left-handed. That could allow police to build a picture of what a criminal looks like not just from sometimes-fuzzy eyewitness accounts, but by analyzing DNA found at a crime scene.

Forensic experts are increasingly relying on DNA as “a genetic eyewitness,” says Jack Ballantyne, associate director for research at the National Center for Forensic Science at the University of Central Florida in Orlando, who is studying whether a DNA sample can reveal a person’s age. {snip}

The push to predict physical features from genetic material is known as DNA forensic phenotyping, and it’s already helped crack some difficult investigations. In 2004, police caught a Louisiana serial killer who eyewitnesses had suggested was white, but whose crime-scene DNA suggested–correctly–that he was black. Britain’s forensic service uses a similar “ethnic inference” test to trace murderers and rapists.

In 2007, a DNA test based on 34 genetic biomarkers developed by Christopher Phillips, a forensic geneticist at the University of Santiago de Compostelo in Spain, indicated that one of the suspects associated with the Madrid bombings was of North African origin. His body was mostly destroyed in an explosion. Using other clues, police later confirmed he had been an Algerian, thereby validating the test results.

But the technique is still in early stages of development, and no one has developed a gene-based police sketch yet. There are big challenges. The technology currently has limited accuracy and can send law enforcement officials on the wrong track. It has also prompted ethical concerns.

For example, tests to assess a person’s ethnic origin won’t always work on people of mixed race. Other times, the conclusion can be ambiguous or unhelpful. “What does it mean to say that the DNA belongs to a ‘light-skinned black man’? It’s a subjective interpretation,” says Pamela Sankar, who is teaches bioethics at the University of Pennsylvania in Philadelphia and has a National Institutes of Health grant to study societal implications of the new technology.

Worried about the ethical and social challenges, Germany doesn’t permit the forensic use of DNA to infer ethnicity or physical traits. Nor do a handful of U.S. states, including Indiana, Wyoming and Rhode Island. The U.K. and the Netherlands allow it.

DNA-based racial profiling “has to be used carefully,” especially in a diverse country like America, says Bert-Jaap Koops of Tilburg University in the Netherlands, who has studied the regulatory picture in different countries. “Some people could make connections between race, crime and genetic disposition” and thereby encourage stigmatization.

But scientists are working to overcome the deficiencies and say that more precise DNA tests for ethnicity and several physical traits are on the horizon.

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Such studies bolster the case for devising a reliable DNA-based test for some physical characteristics. A person’s hair color or skin tone can be relatively easy to predict because the identified genes have a fairly strong effect on the trait. However, it isn’t quite so easy to make a useful prediction about traits such as height or body mass index. That’s because many more genes are likely involved, with each making only a small contribution to the overall effect.

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Similarly, height is a physical trait that’s at least 80% heritable, yet no one has managed to develop a DNA-based test for it. A single gene has been associated with left- or right-handedness. But unlike many genes, examining this one in an adult can’t help solve the lefty-righty question.

Mark Shriver, an anthropologist and geneticist at Pennsylvania State University, has also set himself a daunting challenge: Trying to construct a “picture” of a person’s face by analyzing DNA. He calls the technique “forensic molecular photo fitting,” and it is supported by a $500,000 grant from the U.S. Department of Justice.

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Prof. Shriver focused on 180 genes that have been previously linked to about 400 craniofacial abnormalities, such as cleft lip. He studied their rate of evolution, figuring that if a gene had led to different physical traits in populations–such as shorter noses in one group, for example–it would have evolved faster than other genes. These genes were likely to have been subject to sexual- or natural selection, and the traits associated with them would have been passed down through the generations.

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Prof. Shriver believes he may need samples from at least 8,000 people, including those from other populations, to develop a practical test for facial structure. He estimates it could cost $10 million and five years to get it done.