Fourth Annual DNA Grantees' Workshop
Monday, June 23, 2003
AFTERNOON SESSION
Question-and-Answer Session
MS. TOMSEY: Do we have any questions for any members of our panel? Cecelia?
CECELIA: Barry, did you have to actually run any extra samples to validate this, or did you just go back to all previously run electronic data from the database and just use that?
DR. DUCEMAN: We did both. I can't actually tell you the details. We're actually presenting this for publication with the Journal of Forensic Science but we had old and new batches, so we did both.
QUESTION: My question concerns the first three speakers. There's been recent literature in the clinical chemistry realm and indeed from the obstetrics and gynecology field that suggests that during pregnancy the placenta sheds cells and that you can always detect a Y chromosome in a male child by DNA in the maternal blood. Similarly, work by Nelson and Bianke shows that the cells of the placenta traverse into the maternal circulation and persist in the mother for decades. This phenomenon has come to be called microchymerism.
Now, I think presence of Y-chromosome DNA during pregnancy will have some profound effects for the use of this technology in that state. Do any of you want to talk about this?
DR. PRINZ: Yes, this issue has come up, and for sexual assault kits, will the male cells also be present in the vaginal epithelial cells that you collect during the swabbing? We haven't found any evidence for this. A forensic medical examiner in Germany did some work on that in Austria and Germany. Two things came out: You couldn't find any evidence for the presence of these cells on the vaginal swabs for mothers that had born sons, and you couldn't detect microchymerism with regular PCR (polymerase chain reaction) conditions. If you just use 30 cycles, you will not detect it. You will have to use more than 40 cycles.
MS. TOMSEY: Are there any other questions? Go ahead.
QUESTION: (inaudible).
DR. PRINZ: The question was, if the SRM (standard reference material) samples were single-source male samples, what was our allele-calling threshold? The allele-calling threshold was 100 RFU (relative fluorescent unit) on the 310. We used the recommended 1 nanogram, and the DNA quality was very nice. I'm unsure about the reduced sensitivity. Maybe it was something that we misprogrammed in the cycler. I don't know.
MS. TOMSEY: Any other questions?
QUESTION: A quick one for Mark Perlin—actually two. Assuming that the kits, whatever kits the particular labs are employing, are working very well in terms of balance, if you get one particular locus that somehow is out and your program is doing all the numbers across all the loci, will it just say that one particular locus is inconclusive?
DR. PERLIN: Yes.
QUESTION: Okay. Second, in terms of admissibility, where does it stand in terms of discovery for defense experts wanting to know the background of how the system works?
DR. PERLIN: That's what all those papers and internal validation studies, developmental and all that, are for.
QUESTION: So you'll then provide that for discovery?
DR. PERLIN: I can't say that it's on our Web site yet, but yes.
QUESTION: It can be provided?
DR. PERLIN: Yes.
MS. TOMSEY: Any other questions?
(No response.)
At this time I'd like to thank our panel very much.