Forensic scientists have developed new DNA techniques to meet the unprecedented challenge of identifying those who died in the Twin Towers
IN A private room at Ground Zero lie the unidentified remains of people killed in the collapse of the World Trade Center (WTC). More than 21,800 body parts were recovered from the site - mostly skin and bone fragments - but many were too damaged to extract the DNA that would have helped identify who the victims were. Just 1632 of the estimated 2753 people killed in the attacks have been formally identified. The latest was just last month: Ernest James, who was 40 years old.
Forensic scientists faced an unprecedented challenge. People had been caught up in 1.6 million tonnes of concrete, glass and steel. Fires had burned throughout the recovery operation, and the water that cooled the rubble degraded biological material still further.
The usual techniques of DNA identification were not enough. "It took eight to 10 months to get the remains out of the debris, and what came out was more degraded than you will ever see in an airline disaster," says Beno?t Leclair of Myriad Genetic Laboratories in Salt Lake City, Utah, who contributed to the software that helped identify some of the victims.
In a more usual scenario, complete DNA profiles can be generated from human remains and compared against DNA from relatives. But partial profiles were often the best that could be created from much of the flesh and bone from the Twin Towers. The task of piecing together those profiles fell to Leclair and his colleagues, who built an algorithm to sift through the thousands of partial profiles and search for a match. Eventually, enough fragments could be pieced together to generate a DNA profile that could be compared against reference samples collected from a victim's family (Journal of Forensic Sciences, DOI: 10.1111/j.1556-4029.2007.00456.x).
Two further technologies have been added to the suite already at work on the remains. "Neither were totally new ideas, but they definitely got accelerated by the World Trade Center effort," says Mechthild Prinz of the New York Office of the Chief Medical Examiner, which is leading the work to identify the victims.
To construct a DNA profile, short strands of DNA called primers latch onto the target DNA and are used to make multiple copies of specific chunks of DNA. But when target DNA is heavily damaged, these primers sometimes fail to stick. As a result of the WTC collapse, efforts to create smaller primers that can stick to shorter target regions of DNA were stepped up, says Prinz. The result is a toolkit called MiniFiler.
Investigators also needed better ways of extracting DNA from the tiny fragments of bone collected from Ground Zero, which led to the development of new enzymes and reagents to break down bone's crystal structure. Such techniques are now being used to help identify remains from the battlefield, as well as from crime scenes and disasters worldwide.
Other lessons were learned too. "One is how important it is to collect really good family information," says Prinz. When relatives submitted reference samples of DNA, they often weren't properly documented and the biological relationship of relatives was sometimes unclear, which led to delays.
Prinz says her team is retesting 6000 remains using MiniFiler and the improved bone extraction techniques and comparing these against a database of 20,000 reference samples gathered from victims' families. Relatives will be hoping that like Ernest James's family and friends they will finally get something - even if it is just a scrap of tissue or bone - to say goodbye to.
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