DNA testing has become a widely used tool for understanding biological relationships, tracing ancestry, and assisting in forensic investigations. When performed under proper conditions, these tests are highly accurate and reliable, often yielding results with over 99.9% certainty for inclusions in relationship testing. Despite this high accuracy, various factors, though uncommon, can lead to results that are inaccurate, inconclusive, or complicated to interpret.
Sample Compromise
Reliable test results depend on sample integrity. Contamination, where foreign DNA or substances interfere with the sample, poses a significant risk. This can involve external human DNA, such as skin cells from an individual other than the donor, introduced through improper handling or shared collection tools. Non-human DNA from bacteria, fungi, or other microorganisms present in the sample can also interfere with analysis. Additionally, chemical contamination from certain preservatives or other substances might inhibit the DNA extraction or amplification processes.
Beyond contamination, DNA degradation can severely impact a sample’s usability. DNA can break down due to improper storage conditions, including exposure to extreme temperatures, high humidity, or direct sunlight. Older samples naturally contain less viable DNA, making them more susceptible to degradation. Environmental factors, such as harsh chemicals or prolonged exposure to the elements in forensic contexts, also contribute to DNA breakdown. Compromised samples can result in inconclusive findings, false positives or negatives, or an inability to generate a DNA profile.
Laboratory Mistakes
Errors can occur once a DNA sample reaches the laboratory. Human error, such as mislabeling samples, can lead to results being attributed to the wrong individual. Deviations from established laboratory protocols during DNA extraction, amplification, or analysis can also introduce errors. Mistakes in data entry, during recording or interpretation, can affect the accuracy of the final report.
Cross-contamination is another issue, where DNA from one sample might accidentally transfer to another during processing. This can happen through shared equipment that is not properly sterilized or even via aerosols. Equipment malfunction, such as calibration errors in PCR machines or sequencers, or faulty components, can also affect test outcomes. To minimize these risks, accredited laboratories implement stringent quality control and assurance protocols, ensuring processes are followed precisely and equipment is maintained.
Biological Considerations
Certain biological factors can lead to unexpected or complex DNA test interpretations. Chimerism is a rare condition where an individual possesses two or more genetically distinct cell lines, often from a vanished twin in utero or an organ transplant. This can cause different tissues within the same person to yield varying DNA profiles, potentially complicating relationship tests if the sampled tissue does not reflect the primary genetic makeup.
Recent blood transfusions or bone marrow transplants can also influence DNA test results, particularly if blood or bone marrow samples are used. The recipient’s blood or marrow DNA may temporarily reflect that of the donor, rather than their own genetic profile. This effect is usually transient and primarily impacts tests using these specific tissues, whereas other samples like cheek swabs are typically unaffected. Standard DNA tests cannot differentiate between identical twins, as they share virtually identical DNA, meaning tests show them as indistinguishable. These unique biological scenarios highlight the complexity involved in interpreting some DNA test results.