Monthly Archives: December 2015

Time stamping Steve Avery’s Blood DNA

I recently completed binge watching the entire 10 episodes of Making a Murderer on Netflix. One of the concluding remarks from Steven Avery’s defense team was regarding whether there are new technologies available to better detect EDTA levels or other DNA tests. There was an obsessive fixation on finding more sensitive methods of detecting EDTA in the blood. In my opinion, even if there are new technologies in 2015/2016 to more accurately detect EDTA levels it would not be introducing new evidence.

What if there was a way of time stamping DNA using technology and methods that were not available in 2005? In other words, a method that can distinguish between the DNA from the blood vial from the 1996 version of Steven Avery (aged 34) and the DNA from the blood found in the RAV4 car from the 2005 version of Steven Avery (aged 43). This would hopefully strengthen or weaken the claim that blood was taken from a 1996 vial and was placed in the Toyota RAV4.

The purpose of this post is not to be an insufferable fan-boy amateur detective troll but to share with the world advances in DNA technology and analysis that were not available in 2005 that has a potential to be applied in this case.

A Primer on dna mutations

Disclaimer: This is a very simplistic explanation and any deviation is to ensure that the general public can understand this rather complicated concept.

Each cell in your body contains DNA, this has all the instructions to make a human. The DNA is composed of 4 letters A, C, G and T and each cell has 3 billion of these letters (or sites) in total that make up your genome. On average 1/1000 of these sites are different (i.e. there is a different letter) between two individuals. These sites, where the letters are different between two individuals (i.e. mutations) can be used to identify people. Using enough of these sites will accurately distinguish two individuals and also if two samples are from the same individual. This concept was used to identify the DNA from the pubic hair to be from Gregory Allen and was used to exonerate Steven Avery in 2003 for a crime committed in 1985.

Almost all of these mutations were inherited from your mother and father, in fact 50% from each. However, over the life time of each cell in your body there is a very, very small chance that a mutation will occur in the DNA. These mutations are called somatic mutations. The majority of these mutations are harmless as it has no biological consequences, while others occur in non-dividing cells or cells that rarely divide and thus have no chance to spread the mutations. A subset of these mutations that have biological consequences and occur in dividing cells may result in cancer.

DNA technology

Next Generation DNA Sequencing is a technology that was not available in 2005 and became available and mature from 2007 onwards. This technology allows scientist to read all 3 billion letters (human genome) contained in each of your cells. Prior to 2007,  this was not possible to do in an economical and timely manner and has revolutionized the field of human genetics making large population scale sequencing such as the 1000 genomes project and Exome Aggregation Consortium possible.

Scientific method

This blog post will concentrate on how accumulations of somatic mutations in DNA can be used to determine the relative age of an individual. This is one of several ways that next generation DNA sequencing can be used to approximate the relative age of an individual at the time of DNA extraction. It expands upon a concept introduced in two articles published in the New England Journal of Medicine (NEJM) by researchers from Harvard. The first published by Genovese et. al. and the other by Jaiswal et. al. in the same December 2014 issue of NEJM. The New England Journal of Medicine is one of the most respected journals in medical research.

time stamping dna

The concept introduced by Genovese et. al. and Jaiswal et. al. is that over time very, very rare somatic mutations start accumulating and the older the person the more of these mutations that they harbor (Figure 1 from Jaiswal and Figure 2D from Genovese). The number of somatic mutations are very low in younger individuals but it’s important to note that the search was limited to only genes (~1-2% of the genome) or an even smaller subset of genes known to cause blood cancers. Expanding this search to the whole genome will likely yield more somatic mutations (the majority with no biological consequences) and will be more applicable to younger individuals such as Steven’s earlier time points.

The DNA extracted from blood are from cells created from hematopoietic stem cells. The somatic mutations that can be detected are from stem cells that have divided multiple times to expand in number. This expansion is necessary to contribute to a higher fraction of DNA with these mutations, which later can be detected by sequencing (Figure 1 form Genovese).

The results from both studies, helps to explain the genetic reason why as you age, the risk of getting cancer increases as more time has pass for you to accumulate harmful somatic mutations that go on to cause cancer. A simple analogy would be suppose I am throwing darts at a dart board. I’m pretty bad at darts so the chances of me hitting a bulls-eye is very, very slim. However, if I stand there for a few hours throwing darts, I will eventually hit the bulls-eye. There is also a chance I will never hit the bulls-eye but hey I’m not that uncoordinated! Thus, as you age (hours throwing darts) you are more likely to accumulate somatic mutations that can cause cancer (hitting the bulls-eye). 

Now let’s apply this concept to blood DNA from various time points in Steven Avery’s life: 1985, 1996, 2005 and the present (Figure Below).

SA_DNA_Timeline

Note: Mutation X, Y, Z is use to represent a set of somatic mutations from each of the respective time periods 1985-1996, 1996-2005 and 2005-present.

As Steven ages he accumulates somatic mutations relative to his 1985 DNA sample. Blood DNA from his present-self should have all the somatic mutations identified in 1996 and 2005 (i.e. Mutations X and Y) in addition to any new mutations that occurred between 2005-present (i.e. mutation Z). Somatic mutations (i.e. Mutation Y) that occurred between 1995-2005 are UNIQUE to the 2005 version and can be used to distinguish between the evidence blood vial taken from 1996 and the blood found in the Toyota RAV4 in 2005.

Assumptions made:

  • There are blood samples or DNA extracted from blood for each of the critical time points. I’m assuming during the investigations this was the case.
  • There has been some somatic mutation events (i.e. Mutation Y) in Steven’s blood between 1996 and 2005 and can be detected reliably.
  • The quality and quantity of DNA available is sufficient to perform this analysis.
  • This method and technology is robust to some degree of DNA degradation.
  • Any modification to DNA post-blood draw is distinguishable from somatic mutations (i.e. mutations that occurred within the body)

Conclusion

This method, if applicable would require the development of a test that is robust and reproducible with the appropriate negative and positive controls. The detection limits also needs to be clearly defined. Fortunately, most of this development has been performed by clinical cancer tests. Further development of these tests for this specific application does take time but I have a lot more faith that the time taken by my peers would be far less than the circus of incompetence and stupidity, that is now the US legal system to revisit cases.

Disclaimer: These are my own thoughts and opinions and are completely independent to the institutions and universities that I am employed. Any mistakes in science, logical reasoning, grammar/spelling and lack of eloquence, I blame on my lack of sleep from jet-lag and exhaustion from binge watching 10 episodes in 24 hours! And Santa cuz he never gave me awesome writing skillz this year for Christmas!

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