DNA molecules used to ID patients

The use of DNA molecules has been used by law enforcement agencies to identify individuals, and the technology is also now being used by clinical pathologists to match medical samples with patients and explain discrepancies.

Dr. James Wisecarver of the University of Nebraska Medical Center, which is located in Omaha, gave a presentation on molecular-based identification at the March 29 Introductory Molecular Pathology session of the United States and Canadian Academy of Pathology annual meeting March 24-30 in San Diego. “Human Identification Using Molecular Methods” included background, explanation of techniques, and case examples.

Molecular identification of humans stems from an unexpected medical research find in the 1980s, when researchers studying protein genetics found that DNA includes repeating units which vary from person to person. A technique was developed to identify the difference between individuals using the number of repeating DNA base sequences.

The discovery became known as variable number of tandem repeats, or “VNTRs.” The process requires 20 to 40 bases and results are obtained in one to two weeks. “It requires a fair amount of high-quality intact DNA,” Wisecarver said.

The restriction enzyme digest technique cuts the DNA at a specific code and thus cuts the DNA into specific size fragments. That allows for restriction fragment length polymorphism, or RFLP, to allow the identification of an individual through the DNA sequences.

A polymerase chain reaction (PCR) can amplify small regions of DNA, creating multiple copies of very short DNA sequences to allow for additional analysis.

One use in clinical practice involves bone marrow transplant patients, enabling pathologists to determine whether specific cells originated with the donor or the recipient. Other cases mentioned by Wisecarver involved contaminated tissue, a case in which analysis of a removed prostrate determined no malignancy and which utilized molecular methods to determine that the wrong patient name label had been put on the cancerous sample (the patient whose healthy prostrate was removed obtained a legal settlement from the urologist), and a discrepancy involving a fraternal twin which determined that blood had been transferred to him from his brother while they were in their mother’s womb.

Uses also include verification of identical twins, paternity testing, and quantifiable estimates of how much blood in a transfusion patient is that of the donor and how much is that of the recipient.