Science Questions

Could gene therapy be used to cheat a DNA test?

Sat, 23rd Jun 2012

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Ricardo Santiago asked:

Dear Chris, a question from a podcast listener from Rio de Janeiro, Brazil:


Is it theoretically possible that, in the future, a criminal could change his mouth inner layer cells DNA code (from where he knows a sample will be taken), so as not match anymore the code from the hair or blood cells he left on a crime scene?


How about that as an idea for a police story??


Best regards and enthusiastic praises for all your knowledge and your work on science appreciation!!


Ricardo Santiago


We posed this question to Dr. Paul Debenham Director of Innovation and Development at LGC and Professor Hardev Pandha from the University of Surrey...

Paul -   The possibility proposed is of some sort of sci-fi mouthwash which is DNAable to transfer false DNA profile sequences into your mouth cells.  To achieve an efficient DNA transfer, one would need to piggyback the DNA profiling sequences into a human virus to achieve infection of the mouth cells.  It doesn’t sound the sort of treatment many people would volunteer for.  This treatment will not destroy the existing person’s DNA in their mouth cells, so one would expect to see evidence of a multiple DNA profile and immediately suspect something strange afoot.  Current profiling methods can indicate the presence of more than one source of the DNA when the minor component is of the order of a few percent of the major component.  There are many technical caveats to that ratio, but that's a ballpark figure that people can work with.  If such a mouthwash technique ever became possible, then I could imagine that the sampling procedure deployed would just change to swabbing from a skin surface, plucking out hair roots, or the use of blood, just a pin prick would suffice.

Hannah -   So, even if any or few percent of your own DNA was left in your cheek, DNA fingerprinting is so sensitive that it would still pick up the real you.  But what about grafting tissue containing someone else’s DNA onto your inner cheek?  We ask Surrey University Oncologist, Professor Hardeev Pandha.

Hardeev -   If you do that, the take up of the cells is incredibly inefficient.  It wouldn’t last very long and would most likely be sloughed off or rejected that would be from a different genetic background.  So, it’s a nice idea but I think this is one that won't be a problem for the police forensics folks.

Hannah -   So, rather than trying to change your own DNA, we think that a better way to outwit the justice system would be to deluge the crime scene with other people’s DNA.  For instance, by emptying the contents of a vacuum cleaner bag into the area.  


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There a number of different thing DNA encodes for including protein structure, and gene regulation.  There are also what is called "Untranslated Regions" with no known function, and thus a high degree of variability in structure.

For the DNA that encodes for protein structure, all Human proteins include up to 20 (or 21) Amino Acids, with a specific DNA to protein correspondence.  This would be true with all cells in the human body.  There is, however, a 22nd amino acid, Pyrrolysine that is found in some bacteria, but not in humans. 

All cells in the human body also have essentially the same DNA, although it is likely that there will be at least a couple of spontaneous DNA mutations carried by individuals.  Hardly enough to be picked up by DNA fingerprinting.  There has been some discussion of a Chimera in Sci-Fi literature.  Essentially it is a special case of conjoined (or Siamese) twins, in which a single individual is born, but having the DNA of two siblings (which would be highly related DNA).

I believe current Gene Therapy is an additive process in which viruses are used to add DNA to cells.  If the viral host is cell specific, then the therapy can be cell specific.  Or, perhaps it could only be applied to a single organ.  As far as the Untranslated regions, and DNA fingerprinting, it would not necessarily get rid of a fingerprint, but perhaps could be used to add additional data to a DNA fingerprint, and thus confound the results.

Bone Marrow transplants are a unique form of transplant in which one essentially permanently replaces the cells that form blood with those from another individual.  And, thus, also would replace any blood based DNA fingerprinting.  It can even change a person's blood type.  It is a brutal procedure with a very high mortality rate, and thus would unlikely be used as an elective surgery.  But...  say a criminal with leukemia might get a "new identity".

One thing about a bone marrow transplant is that once completed, the individual will start recognizing the donor's tissue as "self".  So, there would not be any need for anti-transplant rejection medications.  Presumably, after a bone marrow transplant, one could transplant any tissue from the donor without risk of rejection.  An oral swab may not be fooled by a bone marrow transplant.  However, one might be able to also transplant some of the donor's muscle into the inside of one's cheek that would then mucosify (apparently it is relatively easy to get tissue to mucosify in the mouth), and one may not need to transplant the actual mucosa.  But, one could presumably get enough oral mucosa to fool the DNA tests.

Can one do a testicular transplant? CliffordK, Mon, 21st Nov 2011

If DNA-editing technology advances enough to be available to criminals, then DNA-reading technology will presumably be much cheaper and more advanced too.
Forensic police will then be able to economically take more samples - for example, a hair sample will give a history of your DNA over the past few months to years.
It should be possible to take small samples from multiple parts of the body - the movie GATTACA illustrates what someone would have to do to evade sensitive gene sequencing tools. evan_au, Tue, 19th Jun 2012

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