Deoxyribonucleic Acid (DNA) Typing
The forensic scientists at the Armed Forces DNA Identification Laboratory (AFDIL) use the latest DNA typing methods to provide for the identification of remains or other biological evidence. For the identification of current casualties, nuclear DNA (nucDNA) provides a tool for positive identification, when other forensic techniques, such as a fingerprint or dental comparison is not possible. Unfortunately, nucDNA is not a viable tool in older remains due to many environmental factors that cause the nucDNA to degrade. These factors include such things as ultra-violet light from the sun, heat, and moisture. For older remains, however, recovered from the battlefields of Korea, the Cold War, World War II, and Southeast Asia (SEA), mitochondrial DNA (mtDNA) has proved to be a useful investigative tool that adds additional detail towards a positive identification.
Background on DNA
There are only two copies of nucDNA per human cell, except for red blood cells, which have no nucleus. Half of the nucDNA component comes from the biological mother while the other half comes from the biological father. On the other hand, there are hundreds to thousands of copies of mtDNA per cell. Thus, mtDNA analysis is more successful on degraded remains (i.e., Korean War, Cold War and SEA losses) because the amount of mtDNA found in cells and required for analysis lasts a much longer period of time. It is possible that mtDNA stays viable in bones and teeth up to thousands of year if the environmental conditions are favorable.
In looking at nucDNA, a child is a biological copy of the mother and father's because of the inherited nuclear DNA. However, mtDNA is different in that it is only transferred maternally from the mother to the child. An important aspect of mtDNA is that it is an extremely stable genome. Scientists estimate that mutational changes in mtDNA will occur only once in every 40-60 generations, so as long as family relationships can be established, mtDNA provides forensic scientists the ability to go back generations in a family tree to observe these maternal relationships.
One limiting factor of mtDNA is that some DNA sequences are observed more frequently than others. In some of the more common mtDNA sequences, 4-6% of the population can have the same sequence even though they are not know to be maternally related to each other. As a result, mtDNA cannot be used by itself for positive identification and must be coupled with other forensic information to help establish the identity of an individual. However, it is an extremely valuable forensic tool in support of the identification process.
Typing of mtDNA
Typically, the sequencing of mtDNA begins by pulverizing approximately two to three grams of bone or a tooth. The powdered material is then treated with a chemical solution to release the DNA from the cells. Scientists purify this solution to a small volume of extract. Initially, the amount of extracted mtDNA is too small to analyze. Therefore, scientists will replicate a particular region, the "d-loop", of the mtDNA many millions of times using a special chemical process called the Polymerase Chain Reaction (PCR), which was invented in 1985. Technicians determine the sequence of the amplified portion of the mtDNA taken from the extract. Once scientists determine the sequence, they compare it to a family reference sequence to either exclude or provide supportive evidence of the maternal relationship to a particular family.
mtDNA's Support Towards Identifications
mtDNA sequencing is an important tool in DoD's identification process. Scientists count on the power of mtDNA to provide the additional evidence required in making an identification. As with nucDNA, environmental factors such as soil (acidic), weather (moisture), and condition of bones (fragmentation) will often provide extreme challenges to the forensic scientist. Southeast Asia has acidic soil and rain, which accelerates the breakdown of mtDNA. Korea's colder and drier environment, on the other hand, allows for better preservation of the DNA in the remains.
Analysis of mtDNA is extremely accurate; however, mtDNA may not be unique to a single individual. Investigators then require additional presumptive evidence for identification. This presumptive evidence can include other documented findings that provide a logical reason to associate remains with an individual. However, the mtDNA sequence obtained from the biological materials provides the final key scientific evidence that will lead to an answer as to establishing the relationship of the remains with a family reference sequence.
Innovative Usage of mtDNA
Scientists can best use mtDNA on single loss incidents or on a small group of remains. When investigators focus their efforts to a narrowed group, based on presumptive or other collaborative evidence, mtDNA sequence comparison provides the significant additional supportive information towards making an identification.
In cases that involve large numbers of individuals, such as a large battlefield, with possible commingling of remains, there maybe little initial presumptive evidence to help investigators focus the identification process. In these type cases, mtDNA can be useful in grouping the recovered remains into smaller more manageable numbers, so other investigative means can better provide evidence to the identification process. Here scientists will use mtDNA sequences of the remains much earlier in the investigative process as the first step to divide a large group of commingled remains into smaller groups that have the same mtDNA. From scientific study of mtDNA, of the 8,100 American personnel missing in Korea, approximately 5% will have the same mtDNA typing. That is potentially 420 sets of individuals with the same mtDNA sequence. However, the rest of the remains will divide into smaller, more focused groups where investigators may concentrate their efforts. However, the assistance of families is critical if mtDNA is to be used in this manner.
mtDNA Database and Family Outreach
AFDIL scientists require a family database that includes a mtDNA family reference sample for each of the unaccounted-for servicemen to conduct comparisons between remains that have no other presumptive evidence. AFDIL will use the database to compare mtDNA sequencing to exclude or help to identify a returned remain in support of CILHI's identification process.
More than 8,100 servicemen remain unaccounted-for from the Korean War and more than 100 are missing from the Cold War of the 1950s and 60s. Since cessation of hostilities in Korea in 1953, the services have lost contact with many of the families. Consequently, DPMO and the services are conducting a "Family Outreach" program to locate the relatives for servicemen unaccounted-for from the Korean and Cold War. Once these families are located, the Service Casualty Offices will attempt to identify and obtain a maternal blood reference sample. With these samples AFDIL will be able to establish a comprehensive family reference database. Family members of these servicemen should contact the appropriate service casualty office to provide information relative to their loved one.