Sunday, February 28, 2016

Pluto, DNA and the Fool's Gold Standard of Science

The memories haunt. How many times did I discuss DNA findings with a tone of finality? Whether a client, a client's family member, another lawyer, it was always done in sacred tones. "The DNA does not lie" passed my lips more often than I now care to remember.

It turns out the DNA did lie, at least in mixture results, for years.

It has been close to a year since news broke publicly that DNA mixture protocols, or methodology, relied on for many years, changed within the scientific community. This change resulted in a major reduction in the statistical analysis of any given subject's DNA being present in a forensically tested mixture.

Like scientists declassifiying Pluto as a planet in our solar system, DNA interpretation changed. What was a once a high probability of a DNA match in a mixture is now, under new protocol, a possibility, perhaps even a remote one. Pluto did not change. Scientific interpretation of the data changed. Similarly, the DNA material in the mixture did not change, just the interpretation of the data coming FROM the DNA material.

Although the news itself is not new, it is no less disturbing now than when the news first broke.

Now news that interpretation of DNA data has become even more problematic because less and less DNA material is needed for DNA analysis. This means DNA analysis is possible though less DNA material is found on a piece of evidence. The problem? It creates a higher chance of erroneous conclusions because of what goes on both inside, and outside, the testing laboratory.

Carl Zimmer in his New York Times story dated February 26, 2016 explains:
In 1983, the NobelPrize-winning biochemist Kary Mullis sped up the process with a kind of photocopying machine for DNA called polymerase chain reaction, or PCR. Dr. Mullis showed the world how to make millions of copies of any particular genetic fragment.
PCR made it possible for scientists to work with DNA in smaller samples, since they could now make more of it. Over the past four decades, researchers have come up with ways to run ever-more-sensitive tests. In the most extreme of these, experts can reconstruct the entire genome using DNA fragments extracted from a single cell.
The problem?
But the more sensitive DNA tests become, the greater the risk that they will yield the wrong result. Even stray bits of DNA — from a lab worker’s skin cell or an airborne fungal spore — may contaminate the test equipment.
When scientists then run PCR reactions, they may make millions of copies of the contaminating DNA along with the genetic material they want to study. Even a little contamination can skew results.
Perhaps even more of a problem is what occurs before the evidence hits the front door of the testing laboratory. Zimmer's story framed this variant of problem:
But low copy DNA analysis can detect a mix of DNA from more than one person, and it can be hard to tell which of them is relevant to a crime.
'Maybe there’s not three people bleeding on a steering wheel, but there are three people touching it,' said Kirk E. Lohmueller, a geneticist at the University of California, Los Angeles. 'Before, you didn’t have to worry about that.'
People can even leave DNA traces on objects they haven’t touched. In the January issue of The International Journal of Legal Medicine, German researchers vividly illustrated this problem.
They rubbed a cloth on people’s necks, and then gave the cloths to a second group of people. The second group rubbed their hands on the cloth, picking up the DNA from the first group, then handled a plastic bag or a cotton cloth.
When the scientists examined the bags and cloths, they found DNA from the first group of subjects about 40 percent of the time.
DNA, like fingerprinting before it, was considered the gold standard of forensic evidence. What we know now is DNA analysis can be fool's gold. Just like my middle school science teacher was wrong, according to "modern" science, when she taught Pluto was a planet.

1 comment:

  1. But Pluto IS a planet, just a very small one! Nonetheless, excellent deductive reasoning, Monkey Slough, on the analysis of DNA mixtures. I love it when when "standard" protocol must change to catch up with reality.

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