Re: Looking for Information on DNA damage

[Chris Alston <alstonc@odrge.odr.georgetown.edu>]

>From: "Palmer G. Steward, PhD" <psteward@earthlink.net>

>I'm sure there are experts in the area of radiation effects upon forensic
>DNA investigations who can give much more useful info than I.  Just a
>comment incorporating some basic principles:
>
>1.  Dead cells will not repair DNA damage.  Low dose rate is considerable
>less effective than high dose rate presumably due to repair.  If low dose
>rate is about 3 time less effective than high dose rate, I would guess that
>dead cells are at least three times more sensitive to DNA damage than live
>cells.
>
>2.  If the dead cells were dehydrated, then the indirect effect, which
>accounts for most of the damage in hydrated systems, would not be operative.
>Thus dehydrated cells would be considerably less sensitive to DNA damage
>than hydrated cells.  So, was the skeleton kind of desiccated?
>
>3.  The F factor for bone (70 kVp x rays) would be high (more than 1.0).
>DNA within the range of a photo electron from calcium could receive
>considerable more dose than DNA beyond the range of such a photo electron.
>
>4.  70 kVp x rays do not penetrate boney tissue very well.  So the dose
>depends on where the samples were obtained--where the x rays were "bright",
>or in the "shadow".
>
>You pose an interesting question.  I'd be interested in knowing the answer!
>
>Palmer Steward


>>>From: Dunavant Jason D MAJ <Jason.Dunavant@haw.tamc.amedd.army.mil
>>>
>>>
>>>A forensic dentist contacted me looking for information about the dose
>>>levels required to sufficiently damage DNA so that a DNA sequence
>marker(DNA
>>>fingerprint)test would not work (give meaningful results).
>>>
>>>The dentist has approximately 80 sets of remains from the 1950's (Korean
>War
>>>era remains) that could possibly be identified by performing DNA marker
>>>tests on the mitochondria in the cells and then matching the marker test
>>>results with results from maternal descendents.
>>>
>>>During a trial run on two sets of remains, the DNA lab could get no usable
>>>results.  The belief is that the DNA is too damaged to be sequenced.
>During
>>>a document review it was discovered that the remains were examined in 1954
>>>using a fluoroscope which had an output of approximately 50 R/min at
>roughly
>>>70 kVp. The examinations probably took several minutes.  The dentist were
>>>interested in whether the radiation dose that the bones received could
>have
>>>damaged the DNA.  Factors that could affect the result is whether the
>>>radiation would have a different effect on DNA in dead cells rather than
>in
>>>live cells and whether the bones having a lower water content that living
>>>cells could affect the damage.
>>>
>>>Any information, references, or points of contact would be greatly
>>>appreciated.
>>>
>>>JASON DUNAVANT
>>>Chief, Health Physics
>>>Tripler Army Medical Center
>>>1 Jarret White Road, ATTN:  MCHK-PVR
>>>Honolulu, Hawaii 96859-5000
>>>Phone: 808-433-2334
>>>Fax:  808-433-2440
>>>E-mail:  Jason.Dunavant@amedd.army.mil
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