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Persisting fetal microchimerism does not interfere with forensic Y-chromosome typing.
M Klintschar1, P Schwaiger, S Regauer
1Institute of Legal Medicine, University Halle-Wittenberg, Franzosenweg 1, Halle D-06112, Germany. michael.klintschar@medizin.uni-halle.de
Forensic Science International
|March 26, 2004
Summary
Forensic Y-chromosome typing can be impacted by persisting fetal microchimerism. High-sensitivity PCR assays may yield false positives from fetal cells in maternal samples, but routine forensic methods avoid this risk.
Area of Science:
- Forensic Science
- Genetics
- Molecular Biology
Background:
- Forensic Y-chromosome typing analyzes Y-chromosomal polymorphisms in male/female mixed stains, offering high sensitivity for identifying male DNA in cases like rape.
- A potential confounding factor is persisting fetal microchimerism, where male fetal cells can remain in a mother's body for decades after pregnancy.
- The presence of these Y-chromosome-bearing fetal cells in maternal samples, particularly vaginal secretions, could lead to false positive results in forensic analyses.
Purpose of the Study:
- To investigate whether fetal cells with Y-chromosomes can be present in vaginal secretions.
- To determine if these fetal cells can cause false positive results in forensic Y-chromosome typing.
- To evaluate the impact of PCR sensitivity and DNA template quantity on detecting Y-chromosomes from fetal microchimerism.
Main Methods:
- Blood samples from 66 women with sons and 9 vaginal swabs from women without recent sexual activity were analyzed.
- Samples were subjected to PCR amplification of the SRY gene using two protocols: a routine sensitivity assay (10 ng DNA, 30 cycles) and a high-sensitivity assay (200 ng DNA, 45 cycles).
- Positive controls included thyroid tissues with known male fetal microchimerism, and negative controls were blood samples from young girls.
Main Results:
- The routine sensitivity assay (10 ng DNA, 30 cycles) did not yield any positive results for Y-chromosome amplification in the tested samples.
- The high-sensitivity assay (200 ng DNA, 45 cycles) detected SRY amplification in 14% of maternal blood samples and 33% of vaginal swabs.
- These findings indicate that increased PCR sensitivity and DNA input can lead to the detection of Y-chromosomes from fetal cells.
Conclusions:
- Forensic Y-chromosome typing protocols using standard sensitivity (low DNA input, limited PCR cycles) are robust against false positives from persisting fetal microchimerism.
- Highly sensitive PCR methods, when applied to maternal samples, may detect Y-chromosomes from fetal cells, potentially leading to misinterpretations.
- The study confirms that current routine forensic Y-chromosome typing methods effectively mitigate the risk of false positives due to fetal microchimerism.