Friday, October 04, 2002

DNA testing takes time, care, precise methodology

By KIMBERLY O'BRIEN
THE ROANOKE TIMES

   You've probably seen it on one of those television crime shows: Skeletal remains are found, DNA tests are performed and presto! The case is solved, conveniently in a one-hour time slot during prime time.

    Guess what? In real life, it doesn't quite work that way.

    DNA testing takes time, a great deal of care and includes a lot more variables than seen on television. While the public might be wondering what's taking so long for the results of DNA testing on bones suspected of being those of 9-year-old Jennifer Renee Short, the answer is this:

    "That can take time," said Kevin Lothridge, deputy executive director of the National Forensic Science Technology Center in Largo, Fla. "Unfortunately, there are many popular TV shows out there where we see it done in 45 minutes. ... I think everyone has an unrealistic expectation of what can be done."

    DNA, short for deoxyribonucleic acid , is the building block for a person's genetic makeup, governing things such as eye and hair color, stature, even bone density. Because DNA varies from one person to another (except for identical twins), it can be used to identify people or to distinguish one from another.

    In our body, DNA is in our cells, and it's the same in every cell. DNA in someone's blood is the same as in his skin cells, semen and saliva.

    To test DNA, it must first be retrieved from a sample. Depending on the condition of the sample, that can carry varying degrees of difficulty. The preferred method is to use soft tissue - such as skin pieces that might be attached to hair. In the absence of soft tissue, DNA can be extracted from bones.

    But "the bones aren't always the best things to start with," said Dr. Terry Fenger, director of forensic science at Marshall University.

    There are two types of DNA, Fenger said - genomic, the major DNA in everyone's cells, and mitochondrial, a smaller, more resilient form of DNA. When a body deteriorates, genomic DNA may no longer be available. If bones are exposed to the elements, submerged in water or compromised somehow, scientists might try to get a sample of mitochondrial DNA from inside the bone.

    In many cases, both kinds of DNA are collected for a variety of tests, Fenger said.

    Once DNA is extracted, it normally takes three to five days to test it, Fenger said. Then, scientists have to compare the DNA to a known sample from the person, or to the DNA of the person's parents.

    Mitochondrial DNA is best compared to a mother's DNA. Genomic DNA has to match half of the mother's DNA and half of the father's. If samples from the parents aren't readily available, they need to also be extracted for testing. In criminal cases, that can sometimes even involve getting a court order.

    Put it all together, and it takes time.

    Fenger is familiar with the Jennifer Short case and of the bones found Sept. 25 in Rockingham County, N.C. From what he's heard, he doubts that the bones provided the best samples.

    But if genetic material still exists in the bones, DNA testing can be done. And unless it's an extreme case, such as if the bones are very old, you should be able to extract the DNA, Fenger said.

    The testing shouldn't be rushed.

    "When you have a high-profile case, I'm sure they're leaving no stone unturned," Fenger said. "A methodical approach by the investigators and the laboratory team is essential."

Let any elected or appointed official know what you think and how you feel by CLICKING HERE.