Season 3, Episode 5: God of Commerce
The NorBAC team continues to study Patient Zero of the Sinatra virus outbreak, Mark Smith. The San Francisco hospital ships samples of Smith’s organs for analysis. Rachel confirms that only Smith’s kidney was infected with Sinatra, but the kidney contains DNA that doesn’t match DNA from the other organs. The team deduces that Smith must have had a kidney transplant and was taking immunosuppressive drugs, which kept his immune system from overreacting to Sinatra.
 Image provided courtesy of Shaftesbury Films. |
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The team theorizes about why Patient Zero didn’t get sick. |
IS IT POSSIBLE TO IDENTIFY A PERSON’S ETHNIC ORIGIN BY HIS OR HER MITOCHONDRIAL DNA?
What is mitochondrial DNA?
Mitochondria often are referred to as the “powerhouses” of a cell. They break down sugar to produce chemical energy that powers many of the biochemical reactions a cell needs to function. Mitochondria have their own DNA, which is distinct from the DNA in the cell’s nucleus. The mitochondrial DNA – or genome – encodes only about 37 genes compared to the human genome in a cell’s nucleus, which contains about 23,000 genes.
How is mitochondrial DNA passed on?
Unlike a person’s nuclear genes, which are a mixture of genes passed down from that person’s mother and father, mitochondrial DNA is inherited solely from the mother in her eggs. Because of this maternal inheritance, there is no mixing of genes in offspring as happens with nuclear DNA. Therefore, it is possible to “trace” mitochondrial DNA back through many generations.
 Image provided courtesy of AXS Studio Inc. |
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Artist’s rendition of a mitochondrion – its DNA is in its interior, beyond the folded inner membrane. |
How does mitochondrial DNA “encode” ethnic or geographical origin?
As with all DNA, each time mitochondrial DNA is copied, the enzymes that make the copy can incorporate mistakes that lead to changes in the DNA sequence. Scientists have studied the sequences of mitochondrial DNA from many different populations and have determined the migrations throughout history of many populations around the world. These population studies have revealed that certain changes in mitochondrial DNA sequence are associated with certain ancestral populations.
So…
Yes, it is possible that mitochondrial DNA can reveal information about ancestry and origin. The mitochondria in Mark Smith’s kidney must have contained DNA sequences found only in Asian populations, meaning that it must have come from a descendent of an Asian female. It cannot be inferred, however, that the kidney donor looked Asian or lived in Asia.
IS IT PROBABLE THAT A DONATED ORGAN CAN HARBOUR DEADLY VIRUS?
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While performing PCRs on the internal organs that have come in from San Francisco, Rachel is baffled by what she is forced to call “mystery meat.” |
Can organs harbour viruses?
Yes, they can. Sometimes an organ donor becomes infected with a virus shortly before he or she dies; in such a case the person isn’t obviously ill, but does carry the virus. Some viruses become dormant and are permanently entrenched in a person’s tissues after infection. Dubbed ‘latent’ viruses, they do not produce obvious symptoms of infection unless triggered by a physiological change like stress, hormones or illness. The act of transplanting an organ containing a latent virus can often reactivate the virus
Are infected organs used for transplantation?
Unfortunately, this is a risk of organ transplantation. Donors are screened rigorously for their exposure to many common viruses. If somebody has been infected by virus, his or her blood will contain antibodies against that virus. Generally, screening a donor involves looking for the presence of these antibodies. The “health” of the donated organ -- in terms of whether or not it’s infected with virus -- is only as good as the screening process. Often, donated organs are not screened for rare diseases from other parts of the world or emerging diseases because good tests are not available.
So…
It is possible that donated organs, tissues or blood could contain viruses. In some cases, organ recipients have been killed by undetected viruses present in the transplanted organ.
- by Audrey M. Huang, Ph.D.
Want to read and learn more?
To learn more about mitochondrial DNA, visit these sites:
http://ghr.nlm.nih.gov/chromosome=MT
http://en.wikipedia.org/wiki/Human_mitochondrial_genetics
To learn more about using mitochondrial DNA to trace origins, visit the website for National Geographic’s Genographic Project:
https://www3.nationalgeographic.com/genographic/atlas.html
To learn about real viral infection in organ transplant recipients, visit:
http://www.cdc.gov/ncidod/dvbid/westnile/qa/transfusion.htm
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm54d1005a1.htm
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm54d526a1.htm
