NEW YORK (AP) - Investigators using DNA for identification of World Trade Center attacks victims had to find new methods for analyzing thousands of bone and tissue samples, innovations that are expected to push their field forward.
"In terms of DNA identification of mass fatalities, this is a landmark case," said Jack Ballantyne, associate director for research at the National Center for Forensic Science in Orlando, Fla.
Experts in the trade center effort "have developed new technologies and new procedures that would definitely stand the country in good stead" for dealing with future mass disasters, Ballantyne said.
The trade center attacks presented experts with a monumental problem: some 20,000 pieces of bone and tissue, and a list of about 2,800 missing persons. And the crucial DNA from ground zero was often damaged by fire, heat and water.
To pave the way for matches, experts lifted DNA from personal effects like toothbrushes and razors belonging to the missing people, and derived DNA profiles from their relatives.
But when the towers fell, there wasn't any software that could handle the job of matching thousands of those samples to the thousands collected at ground zero, said Bob Shaler, the city's chief of forensic biology.
So, at his request, outside experts went to work writing software, and the job isn't over yet. Shaler's office gets new updates every week to make the process more efficient and easier to use.
Then there's the matter of getting usable DNA data from badly degraded ground zero samples in the first place. Shaler said colleagues at the medical examiner's office perfected a new technique for extracting DNA from decomposing tissue.
Then there is bone. Only about half the 13,000 bone samples processed by Bode Technology Group in Springfield, Va., for Shaler's office gave DNA results good enough to allow immediate use in identification, said Bode lab director Mitchell Holland.
An additional 25 percent gave only partial results, while the remaining 25 percent yielded no DNA results at all, Holland said. Usually, less than 10 percent of samples give no result, he said.
So Bode scientists went to work on two fronts. They tried new procedures and new chemicals to extract more DNA from bones, and they started using a new analysis procedure that lets them analyze DNA fragments only half the size of what they needed before. The shorter chunks are more likely to remain in the fragmented DNA than longer chunks are.
In fact, about half the ground zero samples that gave only partial results before are now giving high quality results for use in identification, Holland said. Bode researchers are also trying the technique on samples that gave no results at all. In any case, the use of smaller DNA segments should help in routine forensic work as well, Holland said.
Another company, Orchid BioSciences Inc. of Princeton, N.J., has found success with a different way of getting information from the tiny pieces of damaged DNA from ground zero. It is looking at a different trait than standard forensic investigations use, one that can be studied with small hunks.
Human DNA can be thought of as long strings of letters, each representing a chemical in a certain position within the famous double helix. It's the sequence of these "letters" that defines the DNA code.
At some places along these long sequences, the code seems to stutter, repeating a short segment again and again. People differ in how many of these repeats they have in various places. Standard forensic analysis counts the number of repeats in 13 different places, plus another spot to determine gender, and the combined result is the DNA profile that can be used for identification.
The Bode researchers do this kind of analysis. The Orchid scientists, in contrast, focus on single letters of the DNA code. In many places along the DNA, where one person has a given letter, many other people have a different letter. Scientists have analyzed DNA based on this variability for some medical and scientific purposes before.
But Orchid has brought large-scale analysis to forensic identification. Workers check what letters appear in 72 places in a sample of DNA, and the overall result is distinctive enough to use in identification, said Mark Stolorow, executive director of Orchid division Orchid Cellmark.
Tests show this approach does work with highly degraded DNA, Stolorow said.
It'll take still more new software to employ that kind of data for trade center remains, Shaler said.
He estimates the identification effort will run another six to eight months. So far, more than 630 victims have been identified by DNA alone, out of more than 1,340 total identifications.
Shaler, who founded the city forensic DNA lab in 1990, said the trade center project has given him new respect for the molecule of life. "DNA," he says, "is a lot hardier than we thought it was."
(Copyright 2002 by The Associated Press. All Rights Reserved.)