DNA identification of Sept. 11 victims continues
Techniques developed after attacks detailed at American Chemical Society meeting
NEW YORK—Two years after the attacks on the World Trade Center here, forensic biologists have identified more than half of the 2782 victims' remains, a member of the New York City Office of Chief Medical Examiner (OCME) said at the annual meeting of the American Chemical Society this week. In the process, they have been forced to come up with new strategies to analyze heavily degraded DNA.
Noelle Umback, a forensic DNA analyst in the OCME's department of forensic biology, said that as of last week, the team had identified 1524, or 54%, of those missing. Of those, 785 were by DNA only, and 219 were by other methods such as dental records or fingerprints. The remainder were identified by a combination of methods or, in some cases, identification by family members. She said that 7857 of about 20,000 recovered remains—ranging from whole bodies to single teeth—had been identified, with DNA hits on 6758 of them.
Umback told The Scientist that the office made four identifications in August, down from an average of 100 a month last year. The straightforward cases are done, she said, leaving those that must be tested and retested. "We have a lot that are on the threshold right now," she said.
The lab faced challenges in analyzing DNA from the World Trade Center site, Umback said, because so much of it was degraded by fires that lasted for months and by the water used to put out those fires. Bone extraction was complicated by calcium dust, which inhibits polymerase chain reaction (PCR). Even the best samples were jumbled together. "It was a giant mortar and pestle as the towers pancaked," Umback said.
The poor quality of the samples meant that when the team used traditional methods of short tandem repeat (STR) PCR, "peaks you knew should be there weren't meeting the threshold" for detection using Promega's PowerPlex 16 system, she said. "The more degradation you have, the more the longer loci will be destroyed." So the team turned to other methods, such as mitochondrial DNA analysis, which is being performed by Celera Genomics, and single nucleotide polymorphism (SNP) analysis, which is being performed by Orchid Biosciences' GeneScreen.
They also made use of John Butler's work on mini-STR analysis, which analyzes smaller regions than standard STR analysis, enabling detection with degraded DNA. The work was helped by the fact that a number of the missing firefighters had given blood samples in the past as part of bone marrow searches.
The team plugged the identification data into the Mass Fatality Identification System, a program developed for them by Gene Codes Corporation. Myriad Genetics and Orchid Biosciences also helped in the effort.
With the work slowing, all but about 15 to 20 of the 100 staff in the lab have gone back to criminal cases. But the work continues, said Umback: "According to Chief Medical Examiner Charles Hirsch, we'll never stop."